Network Working Group Luyuan Fang, Ed.
Internet Draft Cisco Systems, Inc.
Category: Informational
Expires: May 2009
November 2, 2008
Security Framework for MPLS and GMPLS Networks
draft-ietf-mpls-mpls-and-gmpls-security-framework-04.txt
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Abstract
This document provides a security framework for Multiprotocol Label
Switching (MPLS) and Generalized Multiprotocol Label Switching
(GMPLS) Networks (MPLS and GMPLS are described in [RFC3031] and
[RFC3945]). This document addresses the security aspects that are
relevant in the context of MPLS and GMPLS. It describes the
security threats, the related defensive techniques, and the
mechanisms for detection and reporting. This document emphasizes
RSVP-TE and LDP security considerations, as well as Inter-AS and
Inter-provider security considerations for building and maintaining
MPLS and GMPLS networks across different domains or different
Service Providers.
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Table of Contents
1. Introduction..................................................3
1.1. Structure of this Document.................................4
1.2. Authors and Contributors...................................4
2. Terminology...................................................5
2.1. Terminology................................................5
2.2. Acronyms and Abbreviations.................................7
3. Security Reference Models.....................................8
4. Security Threats.............................................10
4.1. Attacks on the Control Plane..............................11
4.2. Attacks on the Data Plane.................................14
5. Defensive Techniques for MPLS/GMPLS Networks.................16
5.1. Authentication............................................17
5.2. Cryptographic Techniques..................................19
5.3. Access Control Techniques.................................29
5.4. Use of Isolated Infrastructure............................33
5.5. Use of Aggregated Infrastructure..........................34
5.6. Service Provider Quality Control Processes................34
5.7. Deployment of Testable MPLS/GMPLS Service.................35
5.8. Verification of Connectivity..............................35
6. Monitoring, Detection, and Reporting of Security Attacks.....35
7. Service Provider General Security Requirements...............36
7.1. Protection within the Core Network........................37
7.2. Protection on the User Access Link........................40
7.3. General User Requirements for MPLS/GMPLS Providers........42
8. Inter-provider Security Requirements.........................43
8.1. Control Plane Protection..................................43
8.2. Data Plane Protection.....................................47
9. Summary of MPLS and GMPLS Security...........................49
9.1. MPLS and GMPLS Specific Security Threats..................49
9.2. Defense Techniques........................................50
9.3. Service Provider MPLS and GMPLS Best Practice Outlines....50
10. Security Considerations....................................51
11. IANA Considerations........................................52
12. Normative References.......................................52
13. Informational References...................................53
14. Author's Addresses.........................................55
15. Acknowledgements...........................................57
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC2119 [RFC
2119].
1. Introduction
Security is an important aspect of all networks, MPLS and GMPLS
networks being no exception.
MPLS and GMPLS are described in [RFC3031] and [RFC3945]. Various
security considerations have been addressed in each of the many
RFCs on MPLS and GMPLS technologies, but no single document covers
general security considerations. The motivation for creating this
document is to provide a comprehensive and consistent security
framework for MPLS and GMPLS networks. Each individual document may
point to this document for general security considerations in
addition to providing security considerations specific to the
particular technologies the document is describing.
In this document, we first describe the security threats relevant
in the context of MPLS and GMPLS and the defensive techniques to
combat those threats. We consider security issues deriving both
from malicious or incorrect behavior of users and other parties and
from negligent or incorrect behavior of providers. An important
part of security defense is the detection and reporting of a
security attack, which is also addressed in this document.
We then discuss possible service provider security requirements in
a MPLS or GMPLS environment. Users have expectations for the
security characteristics of MPLS or GMPLS networks. These include
security requirements for equipment supporting MPLS and GMPLS and
operational security requirements for providers. Service providers
must protect their network infrastructure and make it secure to the
level required to provide services over their MPLS or GMPLS
networks.
Inter-AS and Inter-provider security are discussed with special
emphasis, because the security risk factors are higher with inter-
provider connections.
Depending on different MPLS or GMPLS techniques used, the degree of
risk and the mitigation methodologies vary. This document discusses
the security aspects and requirements for certain basic MPLS and
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GMPLS techniques and inter-connection models. This document does
not attempt to cover all current and future MPLS and GMPLS
technologies, as it is not within the scope of this document to
analyze the security properties of specific technologies.
It is important to clarify that, in this document, we limit
ourselves to describing the providers' security requirements that
pertain to MPLS and GMPLS networks. Readers may refer to the
"Security Best Practices Efforts and Documents" [opsec effort] and
"Security Mechanisms for the Internet" [RFC3631] for general
network operation security considerations. It is not our intention,
however, to formulate precise "requirements" for each specific
technology in terms of defining the mechanisms and techniques that
must be implemented to satisfy such security requirements.
1.1. Structure of this Document
This document is organized as follows. In Section 2, we define the
terminology used. In Section 3, we define the security reference
models for security in MPLS/GMPLS networks, which we use in the
rest of the document. In Section 4, we describe the security
threats specific to MPLS and GMPLS. In Section 5, we review
defensive techniques that may be used against those threats. In
Section 6, we describe how attacks may be detected and reported. In
Section 7, we describe security requirements providers may have to
guarantee the security of the network infrastructure for MPLS/GMPLS
services. In section 8, we discuss Inter-provider security
requirements. Finally, in Section 9, we discuss security
considerations for this document.
This document has used relevant content from RFC 4111 "Security
Framework of Provider Provisioned VPN for Provider-Provisioned
Virtual Private Networks (PPVPNs)" [RFC4111], and "MPLS
InterCarrier Interconnect Technical Specification" [MFA MPLS ICI]
in the Inter-provider security discussion. We acknowledge the
authors of these documents for the valuable information and text.
1.2. Authors and Contributors
Authors:
Luyuan Fang, Ed., Cisco Systems, Inc.
Michael Behringer, Cisco Systems, Inc.
Ross Callon, Juniper Networks
J. L. Le Roux, France Telecom
Raymond Zhang, British Telecom
Paul Knight, Nortel
Yaakov Stein, RAD Data Communications
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Nabil Bitar, Verizon
Richard Graveman, RFC Security, LLC
Monique Morrow, Cisco Systems, Inc.
Adrian Farrel, Old Dog Consulting
As a design team member for the MPLS Security Framework, Jerry Ash
also made significant contributions to this document.
2. Terminology
2.1. Terminology
This document uses MPLS and GMPLS specific terminology. Definitions
and details about MPLS and GMPLS terminology can be found in
[RFC3031] and [RFC3945]. The most important definitions are
repeated in this section; for other definitions the reader is
referred to [RFC3031] and [RFC3945].
Customer Edge (CE) device: A Customer Edge device is a router or a
switch in the customer's network interfacing with the Service
Provider's network.
Forwarding Equivalence Class (FEC): A group of IP packets that are
forwarded in the same manner (e.g., over the same path, with the
same forwarding treatment).
Label: A short, fixed length, physically contiguous identifier used
to identify a FEC, usually of local significance.
Label Switched Hop: A hop between two MPLS nodes, on which
forwarding is done using labels.
Label Switched Path (LSP): The path through one or more LSRs at one
level of the hierarchy followed by a packets in a particular FEC.
Label Switching Router (LSR): An MPLS node capable of forwarding
native IP packets.
Loop Detection: A method of dealing with loops in which loops are
allowed to be set up, and data may be transmitted over the loop,
but the loop is later detected.
Loop Prevention: A method of dealing with loops in which data is
never transmitted over a loop.
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Label Stack: An ordered set of labels.
Merge Point: A node at which label merging is done.
MPLS Domain: A contiguous set of nodes that perform MPLS routing
and forwarding and are also in one Routing or Administrative
Domain.
MPLS Edge Node: A MPLS node that connects a MPLS domain with a node
outside of the domain, either because it does not run MPLS, or
because it is in a different domain. Note that if a LSR has a
neighboring host not running MPLS, then that LSR is a MPLS edge
node.
MPLS Egress Node: A MPLS edge node in its role in handling traffic
as it leaves a MPLS domain.
MPLS Ingress Node: A MPLS edge node in its role in handling traffic
as it enters a MPLS domain.
MPLS Label: A label carried in a packet header, which represents
the packet's FEC.
MPLS Node: A node running MPLS. A MPLS node is aware of MPLS
control protocols, runs one or more routing protocols, and is
capable of forwarding packets based on labels. A MPLS node may
optionally be also capable of forwarding native IP packets.
MultiProtocol Label Switching (MPLS): An IETF working group and the
effort associated with the working group.
P: Provider Router. A Provider Router is a router in the Service
Provider's core network that does not have interfaces directly
towards the customer. A P router is used to interconnect the PE
routers.
PE: Provider Edge device. A Provider Edge device is the equipment
in the Service Provider's network that interfaces with the
equipment in the customer's network.
Core network: A MPLS/GMPLS core network is defined as the central
network infrastructure which consists of P and PE routers. A
MPLS/GMPLS core network may consist of one or more networks belong
to a single SP.
VPN: Virtual Private Network, which restricts communication between
a set of sites, making use of an IP backbone shared by traffic not
going to or not coming from those sites ([RFC4110]).
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2.2. Acronyms and Abbreviations
AS Autonomous System
ASBR Autonomous System Border Router
ATM Asynchronous Transfer Mode
BGP Border Gateway Protocol
BFD Bidirectional Forwarding Detection
CE Customer-Edge device
CoS Class of Service
CPU Central Processor Unit
DNS Domain Name System
DoS Denial of Service
FEC Forwarding Equivalence Class
GMPLS Generalized Multi-Protocol Label Switching
GRE Generic Routing Encapsulation
ICI InterCarrier Interconnect
ICMP Internet Control Message Protocol
ICMPv6 ICMP in IP Version 6
IGP Interior Gateway Protocol
IKE Internet Key Exchange
IP Internet Protocol
IPsec IP Security
IPVPN IP-based VPN
LDP Label Distribution Protocol
L2TP Layer 2 Tunneling Protocol
LMP Link Management Protocol
LSP Label Switched Path
LSR Label Switching Router
MD5 Message Digest Algorithm
MPLS MultiProtocol Label Switching
MP-BGP Multi-Protocol BGP
NTP Network Time Protocol
OAM Operations, Administration, and Management
PCE Path Computation Element
PE Provider-Edge device
PPVPN Provider-Provisioned Virtual Private Network
PSN Packet-Switched Network
PW Pseudowire
QoS Quality of Service
RR Route Reflector
RSVP Resource Reservation Protocol
RSVP-TE Resource Reservation Protocol with Traffic Engineering
Extensions
SLA Service Level Agreement
SNMP Simple Network Management Protocol
SP Service Provider
SSH Secure Shell
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SSL Secure Sockets Layer
SYN Synchronize packet in TCP
TCP Transmission Control Protocol
TDM Time Division Multiplexing
TE Traffic Engineering
TLS Transport Layer Security
ToS Type of Service
TTL Time-To-Live
UDP User Datagram Protocol
VC Virtual Circuit
VPN Virtual Private Network
WG Working Group of IETF
WSS Web Services Security
3. Security Reference Models
This section defines a reference model for security in MPLS/GMPLS
networks.
This document defines each MPLS/GMPLS core in a single domain to be
a trusted zone. A primary concern is about security aspects that
relate to breaches of security from the "outside" of a trusted zone
to the "inside" of this zone. Figure 1 depicts the concept of
trusted zones within the MPLS/GMPLS framework.
/-------------\
+------------+ / \ +------------+
| MPLS/GMPLS +---/ \--------+ MPLS/GMPLS |
| user | MPLS/GMPLS Core | user |
| site +---\ /XXX-----+ site |
+------------+ \ / XXX +------------+
\-------------/ | |
| |
| +------\
+--------/ "Internet"
MPLS/GMPLS Core with user connections and Internet connection
Figure 1: The MPLS/GMPLS trusted zone model.
The trusted zone is the MPLS/GMPLS core in a single AS within a
single Service Provider.
The boundaries of a trust domain should be carefully defined when
analyzing the security property of each individual network, e.g.,
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the boundaries can be at the link termination, remote peers, areas,
or quite commonly, ASes.
In principle, the trusted zones should be separate; however,
typically MPLS core networks also offer Internet access, in which
case a transit point (marked with "XXX" in Figure 1) is defined. In
the case of MPLS/GMPLS inter-provider connections, the trusted zone
of each provider ends at the respective ASBRs (ASBR1 and ASBR2 for
Provider A, ASBR3 and ASBR4 for Provider B).
A key requirement of MPLS and GMPLS networks is that the security
of the trusted zone not be compromised by interconnecting the
MPLS/GMPLS core infrastructure with another provider's core
(MPLS/GMPLS or non-MPLS/GMPLS), the Internet, or end users.
In addition, neighbors may be trusted or untrusted. Neighbors may
be authorized or unauthorized. Even though a neighbor may be
authorized for communication, it may not be trusted. For example,
when connecting with another provider's ASBRs to set up inter-AS
LSPs, the other provider is considered an untrusted but authorized
neighbor.
+---------------+ +----------------+
| | | |
| MPLS/GMPLS ASBR1----ASBR3 MPLS/GMPLS |
CE1--PE1 Network | | Network PE2--CE2
| Provider A ASBR2----ASBR4 Provider B |
| | | |
+---------------+ +----------------+
For Provider A:
Trusted Zone: Provider A MPSL/GMPLS network
Trusted neighbors: PE1, ASBR1, ASBR2
Authorized but untrusted neighbor: provider B
Unauthorized neighbors: CE1, CE2
Figure 2. MPLS/GMPLS trusted zone and authorized neighbor.
All aspects of network security independent of whether a network is
a MPLS/GMPLS network are out of scope. For example, attacks from
the Internet to a user's web-server connected through the
MPLS/GMPLS network are not considered here, unless the way the
MPLS/GMPLS network is provisioned could make a difference to the
security of this user's server.
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4. Security Threats
This section discusses the various network security threats that
may endanger MPLS/GMPLS networks. The discussion is limited to
those threats that are unique to MPLS/GMPLS networks or that affect
MPLS/GMPLS network in unique ways.
A successful attack on a particular MPLS/GMPLS network or on a SP's
MPLS/GMPLS infrastructure may cause one or more of the following
ill effects:
- Observation, modification, or deletion of a provider's or user's
data.
- Replay of a provider's or user's data.
- Injection of inauthentic data into a provider's or user's
traffic stream.
- Traffic pattern analysis on a provider's or user's traffic.
- Disruption of a provider's or user's connectivity.
- Degradation of a provider's service quality.
It is useful to consider that threats, whether malicious or
accidental, may come from different categories of sources. For
example they may come from:
- Other users whose services are provided by the same MPLS/GMPLS
core.
- The MPLS/GMPLS SP or persons working for it.
- Other persons who obtain physical access to a MPLS/GMPLS SP's
site.
- Other persons who use social engineering methods to influence
the behavior of a SP's personnel.
- Users of the MPLS/GMPLS network itself, e.g., intra-VPN threats.
(Such threats are beyond the scope of this document.)
- Others, e.g., attackers from the Internet at large.
- Other SPs in the case of MPLS/GMPLS Inter-
provider connection. The core of the other provider may or may
not be using MPLS/GMPLS.
- Those who create, deliver, install, and maintain software for
network equipment.
Given that security is generally a tradeoff between expense and
risk, it is also useful to consider the likelihood of different
attacks occurring. There is at least a perceived difference in the
likelihood of most types of attacks being successfully mounted in
different environments, such as:
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- A MPLS/GMPLS core inter-connecting with another provider's core
- A MPLS/GMPLS configuration transiting the public Internet
Most types of attacks become easier to mount and hence more likely
as the shared infrastructure via which service is provided expands
from a single SP to multiple cooperating SPs to the global
Internet. Attacks that may not be of sufficient likeliness to
warrant concern in a closely controlled environment often merit
defensive measures in broader, more open environments. In closed
communities, it is often practical to deal with misbehavior after
the fact: an employee can be disciplined, for example.
The following sections discuss specific types of exploits that
threaten MPLS/GMPLS networks.
4.1. Attacks on the Control Plane
This category encompasses attacks on the control structures
operated by the SP with MPLS/GMPLS cores.
It should be noted that while connectivity in the MPLS control plane
uses the same links and network resources as are used by the data
plane, the GMPLS control plane may be provided by separate resources
from those used in the data plane. That is, the GMPLS control plane
may be physically diverse from the data plane.
The different cases of physically congruent and physically diverse
control/data planes lead to slightly different possibilities of
attack, although most of the cases are the same. Note that, for
example, the data plane cannot be directly congested by an attack on
a physically diverse control plane as it could be if the control and
data planes shared network resources. Note also that if the control
plane uses diverse resources from the data plane, no assumptions
should be made about the security of the control plane based on the
security of the data plane resources.
4.1.1. LSP creation by an unauthorized element
The unauthorized element can be a local CE or a router in another
domain. An unauthorized element can generate MPLS signaling
messages. At the least, this can result in extra control plane and
forwarding state, and if successful, network bandwidth could be
reserved unnecessarily. This may also result in theft of service or
even compromise the entire network.
4.1.2. LSP message interception
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This threat might be accomplished by monitoring network traffic,
for example, after a physical intrusion. Without physical
intrusion, it could be accomplished with an unauthorized software
modification. Also many technologies such as terrestrial microwave,
satellite, or free-space optical could be intercepted without
physical intrusion. If successful, it could provide information
leading to label spoofing attacks. It also raises confidentiality
issues.
4.1.3. Attacks against RSVP-TE
RSVP-TE, described in [RFC3209], is the control protocol used to
set up GMPLS and traffic engineered MPLS tunnels.
There are two major types of Denial of Service (DoS) attacks
against a MPLS domain based on RSVP-TE. The attacker may set up
numerous unauthorized LSPs or may send a storm of RSVP messages.
It has been demonstrated that unprotected routers running RSVP can
be effectively disabled by both types of DoS attacks.
These attacks may even be combined, by using the unauthorized LSPs
to transport additional RSVP (or other) messages across routers
where they might otherwise be filtered out. RSVP attacks can be
launched against adjacent routers at the border with the attacker,
or against non-adjacent routers within the MPLS domain, if there is
no effective mechanism to filter them out.
4.1.4. Attacks against LDP
LDP, described in [RFC5036], is the control protocol used to set up
MPLS tunnels without TE.
There are two significant types of attack against LDP. An
unauthorized network element can establish a LDP session by sending
LDP Hello and LDP Init messages, leading to the potential setup of
a LSP, as well as accompanying LDP state table consumption. Even
without successfully establishing LSPs, an attacker can launch a
DoS attack in the form of a storm of LDP Hello messages or LDP TCP
Syn messages, leading to high CPU utilization on the target router.
4.1.5. Denial of Service Attacks on the Network
Infrastructure
DoS attacks could be accomplished through a MPLS signaling storm,
resulting in high CPU utilization and possibly leading to control
plane resource starvation.
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Control plane DoS attacks can be mounted specifically against the
mechanisms the SP uses to provide various services, or against the
general infrastructure of the service provider, e.g., P routers or
shared aspects of PE routers. (An attack against the general
infrastructure is within the scope of this document only if the
attack can occur in relation with the MPLS/GMPLS infrastructure;
otherwise is not a MPLS/GMPLS-specific issue.)
The attacks described in the following sections may each have
denial of service as one of their effects. Other DoS attacks are
also possible.
4.1.6. Attacks on the SP's MPLS/GMPLS Equipment via
Management Interfaces
This includes unauthorized access to a SP's infrastructure
equipment, for example to reconfigure the equipment or to extract
information (statistics, topology, etc.) pertaining to the network.
4.1.7. Social Engineering Attacks on the SP's
Infrastructure
Attacks in which the service provider network is reconfigured or
damaged, or in which confidential information is improperly
disclosed, may be mounted by manipulation of a SP's personnel.
These types of attacks are MPLS/GMPLS-specific if they affect
MPLS/GMPLS-serving mechanisms.
4.1.8. Cross-Connection of Traffic between Users
This refers to the event in which expected isolation between
separate users (who may be VPN users) is breached. This includes
cases such as:
- A site being connected into the "wrong" VPN
- Traffic being replicated and sent to an unauthorized user
- Two or more VPNs being improperly merged together
- A point-to-point VPN connecting the wrong two points
- Any packet or frame being improperly delivered outside the VPN
to which it belongs
Mis-connection or cross-connection of VPNs may be caused by service
provider or equipment vendor error, or by the malicious action of
an attacker. The breach may be physical (e.g., PE-CE links mis-
connected) or logical (e.g., improper device configuration).
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Anecdotal evidence suggests that the cross-connection threat is one
of the largest security concerns of users (or would-be users).
4.1.9. Attacks against Routing Protocols
This encompasses attacks against underlying routing protocols that
are run by the SP and that directly support the MPLS/GMPLS core.
(Attacks against the use of routing protocols for the distribution
of backbone routes are beyond the scope of this document.)
Specific attacks against popular routing protocols have been widely
studied and described in [RFC4593].
4.1.10. Other Attacks on Control Traffic
Besides routing and management protocols (covered separately in the
previous sections), a number of other control protocols may be
directly involved in delivering services by the MPLS/GMPLS core.
These include but may not be limited to:
- MPLS signaling (LDP, RSVP-TE) discussed above in subsections
4.1.4 and 4.1.3
- PCE signaling
- IPsec signaling (IKE and IKEv2)
- ICMP and ICMPv6
- L2TP
- BGP-based membership discovery
- Database-based membership discovery (e.g., RADIUS)
- Other protocols that may be important to the control
infrastructure, e.g., DNS, LMP, NTP, SNMP, and GRE.
Attacks might subvert or disrupt the activities of these protocols,
for example via impersonation or DoS.
Note that all of the data plane attacks can also be done on the
packets of the control and management planes: insertion, spoofing,
replay, deletion, pattern analysis, and other attacks mentioned
above.
4.2. Attacks on the Data Plane
This category encompasses attacks on the provider's or end user's
data. Note that from the MPLS/GMPLS network end user's point of
view, some of this might be control plane traffic, e.g. routing
protocols running from user site A to user site B via an IP or non-
IP connections, which may be some type of VPN.
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4.2.1. Unauthorized Observation of Data Traffic
This refers to "sniffing" provider or end user packets and
examining their contents. This can result in exposure of
confidential information. It can also be a first step in other
attacks (described below) in which the recorded data is modified
and re-inserted, or simply replayed later.
4.2.2. Modification of Data Traffic
This refers to modifying the contents of packets as they traverse
the MPLS/GMPLS core.
4.2.3. Insertion of Inauthentic Data Traffic: Spoofing
and Replay
Spoofing refers to sending a user or inserting into a data stream
packets that do not belong, with the objective of having them
accepted by the recipient as legitimate. Also included in this
category is the insertion of copies of once-legitimate packets that
have been recorded and replayed.
4.2.4. Unauthorized Deletion of Data Traffic
This refers to causing packets to be discarded as they traverse the
MPLS/GMPLS networks. This is a specific type of Denial of Service
attack.
4.2.5. Unauthorized Traffic Pattern Analysis
This refers to "sniffing" provider or user packets and examining
aspects or meta-aspects of them that may be visible even when the
packets themselves are encrypted. An attacker might gain useful
information based on the amount and timing of traffic, packet
sizes, source and destination addresses, etc. For most users, this
type of attack is generally considered to be significantly less of
a concern than the other types discussed in this section.
4.2.6. Denial of Service Attacks
Denial of Service (DoS) attacks are those in which an attacker
attempts to disrupt or prevent the use of a service by its
legitimate users. Taking network devices out of service, modifying
their configuration, or overwhelming them with requests for service
are several of the possible avenues for DoS attack.
Overwhelming the network with requests for service, otherwise known
as a "resource exhaustion" DoS attack, may target any resource in
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the network, e.g., link bandwidth, packet forwarding capacity,
session capacity for various protocols, CPU power, table size,
storage overflows, and so on.
DoS attacks of the resource exhaustion type can be mounted against
the data plane of a particular provider or end user by attempting
to insert (spoofing) an overwhelming quantity of inauthentic data
into the provider or end user network from the outside of the
trusted zone. Potential results might be to exhaust the bandwidth
available to that provider or end user or to overwhelm the
cryptographic authentication mechanisms of the provider or end
user.
Data plane resource exhaustion attacks can also be mounted by
overwhelming the service provider's general (MPLS/GMPLS-
independent) infrastructure with traffic. These attacks on the
general infrastructure are not usually a MPLS/GMPLS-specific issue,
unless the attack is mounted by another MPLS/GMPLS network user
from a privileged position. (E.g., a MPLS/GMPLS network user might
be able to monopolize network data plane resources and thus disrupt
other users.)
Many DoS attacks use amplification, whereby the attacker co-opts
otherwise innocent parties to increase the effect of the attack.
The attacker may, for example, send packets to a broadcast or
multicast address with the spoofed source address of the victim,
and all of the recipients may then respond to the victim.
4.2.7. Misconnection
Misconnection may arise through deliberate attack, or through
misconfiguration or misconnection of the network resources. The
result is likely to be delivery of data to the wrong destination or
black-holing of the data.
In GMPLS with physically diverse control and data planes, it may be
possible for data plane misconnection to go undetected by the
control plane.
In optical networks under GMPLS control, misconnection may give rise
to physical safety risks as unprotected lasers may be activated
without warning.
5. Defensive Techniques for MPLS/GMPLS Networks
The defensive techniques discussed in this document are intended to
describe methods by which some security threats can be addressed.
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They are not intended as requirements for all MPLS/GMPLS
implementations. The MPLS/GMPLS provider should determine the
applicability of these techniques to the provider's specific
service offerings, and the end user may wish to assess the value of
these techniques to the user's service requirements. The
operational environment determines the security requirements.
Therefore, protocol designers need to provide a full set of
security services, which can be used where appropriate.
The techniques discussed here include encryption, authentication,
filtering, firewalls, access control, isolation, aggregation, and
other techniques.
Often, security is achieved by careful protocol design, rather than
by adding a security method. For example, one method of mitigating
DoS attacks is to make sure that innocent parties cannot be used to
amplify the attack. Security works better when it is "designed in"
rather than "added on."
Nothing is ever 100% secure. Defense therefore involves protecting
against those attacks that are most likely to occur or that have
the most direct consequences if successful. For those attacks that
are protected against, absolute protection is seldom achievable;
more often it is sufficient just to make the cost of a successful
attack greater than what the adversary will be willing or able to
expend.
Successfully defending against an attack does not necessarily mean
the attack must be prevented from happening or from reaching its
target. In many cases the network can instead be designed to
withstand the attack. For example, the introduction of inauthentic
packets could be defended against by preventing their introduction
in the first place, or by making it possible to identify and
eliminate them before delivery to the MPLS/GMPLS user's system.
The latter is frequently a much easier task.
5.1. Authentication
To prevent security issues arising from some Denial-of-Service
attacks or from malicious or accidental misconfiguration, it is
critical that devices in the MPLS/GMPLS should only accept
connections or control messages from valid sources. Authentication
refers to methods to ensure that message sources are properly
identified by the MPLS/GMPLS devices with which they communicate.
This section focuses on identifying the scenarios in which sender
authentication is required and recommends authentication mechanisms
for these scenarios.
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Cryptographic techniques (authentication, integrity, and
encryption) do not protect against some types of denial of service
attacks, specifically resource exhaustion attacks based on CPU or
bandwidth exhaustion. In fact, the processing required to decrypt
or check authentication may, in the case of software-based
cryptographic processing, in some cases increase the effect of
these resource exhaustion attacks. With a hardware cryptographic
accelerator, attack packets can be dropped at line speed without a
cost of software cycles. Cryptographic techniques may, however, be
useful against resource exhaustion attacks based on exhaustion of
state information (e.g., TCP SYN attacks).
The MPLS data plane, as presently defined, is not amenable to
source authentication as there are no source identifiers in the
MPLS packet to authenticate. The MPLS label is only locally
meaningful. It may be assigned by a downstream node or upstream
node for multicast support.
When the MPLS payload carries identifiers that may be authenticated
(e.g., IP packets), authentication may be carried out at the client
level, but this does not help the MPLS SP, as these client
identifiers belong to an external, untrusted network.
5.1.1. Management System Authentication
Management system authentication includes the authentication of a
PE to a centrally-managed network management or directory server
when directory-based "auto-discovery" is used. It also includes
authentication of a CE to the configuration server, when a
configuration server system is used.
5.1.2. Peer-to-Peer Authentication
Peer-to-peer authentication includes peer authentication for
network control protocols (e.g., LDP, BGP, etc.), and other peer
authentication (i.e., authentication of one IPsec security gateway
by another).
Authentication should be bi-directional, including PE or CE to
configuration server authentication for PE or CE to be certain it
is communicating with the right server.
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5.1.3. Cryptographic techniques for authenticating identity
Cryptographic techniques offer several mechanisms for
authenticating the identity of devices or individuals. These
include the use of shared secret keys, one-time keys generated by
accessory devices or software, user-ID and password pairs, and a
range of public-private key systems. Another approach is to use a
hierarchical Certification Authority system to provide digital
certificates.
This section describes or provides references to the specific
cryptographic approaches for authenticating identity. These
approaches provide secure mechanisms for most of the authentication
scenarios required in securing a MPLS/GMPLS network.
5.2. Cryptographic Techniques
MPLS/GMPLS defenses against a wide variety of attacks can be
enhanced by the proper application of cryptographic techniques.
These are the same cryptographic techniques that are applicable to
general network communications. In general, these techniques can
provide confidentiality (encryption) of communication between
devices, can authenticate the identities of the devices, and can
ensure that it will be detected if the data being communicated is
changed during transit.
Several aspects of authentication are addressed in some detail in a
separate "Authentication" section.
Cryptographic methods add complexity to a service and thus, for a
few reasons, may not be the most practical solution in every case.
Cryptography adds an additional computational burden to devices,
which may reduce the number of user connections that can be handled
on a device or otherwise reduce the capacity of the device,
potentially driving up the provider's costs. Typically,
configuring encryption services on devices adds to the complexity
of their configuration and adds labor cost. Some key management
system is usually needed. Packet sizes are typically increased when
the packets are encrypted or have integrity checks or replay
counters added, increasing the network traffic load and adding to
the likelihood of packet fragmentation with its increased overhead.
(This packet length increase can often be mitigated to some extent
by data compression techniques, but at the expense of additional
computational burden.) Finally, some providers may employ enough
other defensive techniques, such as physical isolation or filtering
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and firewall techniques, that they may not perceive additional
benefit from encryption techniques.
Users may wish to provide confidentiality end to end. Generally,
encrypting for confidentiality must be accompanied with
cryptographic integrity checks to prevent certain active attacks
against the encrypted communications. On today's processors,
encryption and integrity checks run extremely quickly, but key
management may be more demanding in terms of both computational and
administrative overhead.
The trust model among the MPLS/GMPLS user, the MPLS/GMPLS provider,
and other parts of the network is a major element in determining
the applicability of cryptographic protection for any specific
MPLS/GMPLS implementation. In particular, it determines where
cryptographic protection should be applied:
- If the data path between the user's site and the
provider's PE is not trusted, then it may be used on the
PE-CE link.
- If some part of the backbone network is not trusted,
particularly in implementations where traffic may travel
across the Internet or multiple providers' networks, then
the PE-PE traffic may be cryptographically protected. One
also should consider cases where L1 technology may be
vulnerable to eavesdropping.
- If the user does not trust any zone outside of its
premises, it may require end-to-end or CE-CE cryptographic
protection. This fits within the scope of this MPLS/GMPLS
security framework when the CE is provisioned by the
MPLS/GMPLS provider.
- If the user requires remote access to its site from a
system at a location that is not a customer location (for
example, access by a traveler) there may be a requirement
for cryptographically protecting the traffic between that
system and an access point or a customer's site. If the
MPLS/GMPLS provider supplies the access point, then the
customer must cooperate with the provider to handle the
access control services for the remote users. These access
control services are usually protected cryptographically,
as well.
Access control usually starts with authentication of the
entity. If cryptographic services are part of the scenario,
then it is important to bind the authentication to the key
management. Otherwise the protocol is vulnerable to being
hijacked between the authentication and key management.
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Although CE-CE cryptographic protection can provide integrity and
confidentiality against third parties, if the MPLS/GMPLS provider
has complete management control over the CE (encryption) devices,
then it may be possible for the provider to gain access to the
user's traffic or internal network. Encryption devices could
potentially be reconfigured to use null encryption, bypass
cryptographic processing altogether, reveal internal configuration,
or provide some means of sniffing or diverting unencrypted traffic.
Thus an implementation using CE-CE encryption needs to consider the
trust relationship between the MPLS/GMPLS user and provider.
MPLS/GMPLS users and providers may wish to negotiate a service
level agreement (SLA) for CE-CE encryption that provides an
acceptable demarcation of responsibilities for management of
cryptographic protection on the CE devices. The demarcation may
also be affected by the capabilities of the CE devices. For
example, the CE might support some partitioning of management, a
configuration lock-down ability, or shared capability to verify the
configuration. In general, the MPLS/GMPLS user needs to have a
fairly high level of trust that the MPLS/GMPLS provider will
properly provision and manage the CE devices, if the managed CE-CE
model is used.
5.2.1. IPsec in MPLS/GMPLS
IPsec [RFC4301] [RFC4302] [RFC4835] [RFC4306] [RFC2411] is the
security protocol of choice for encryption at the IP layer. IPsec
provides robust security for IP traffic between pairs of devices.
Non-IP traffic such as IS-IS routing must be converted to IP (e.g.,
by encapsulation) in order to use IPsec.
In the MPLS/GMPLS model, IPsec can be employed to protect IP
traffic between PEs, between a PE and a CE, or from CE to CE. CE-
to-CE IPsec may be employed in either a provider-provisioned or a
user-provisioned model. Likewise, IPsec protection of data
performed within the user's site is outside the scope of this
document, because it is simply handled as user data by the
MPLS/GMPLS core. However, if the SP performs compression, pre-
encryption will have a major effect on that operation.
IPsec does not itself specify an encryption algorithm. It can use
a variety of integrity or confidentiality algorithms (or even
combined integrity and confidentiality algorithms), with various
key lengths, such as AES encryption or AES message integrity
checks. There are trade-offs between key length, computational
burden, and the level of security of the encryption. A full
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discussion of these trade-offs is beyond the scope of this
document. In practice, any currently recommended IPsec protection
offers enough security to reduce the likelihood of its being
directly targeted by an attacker substantially; other weaker links
in the chain of security are likely to be attacked first.
MPLS/GMPLS users may wish to use a Service Level Agreement (SLA)
specifying the SP's responsibility for ensuring data integrity and
confidentiality, rather than analyzing the specific encryption
techniques used in the MPLS/GMPLS service.
Encryption algorithms generally come with two parameters: mode such
as Cipher Block Chaining and key length such as AES-192. (This
should not be confused with two other senses in which the word
"mode" is used: IPsec itself can be used in Tunnel Mode or
Transport Mode, and IKE [version 1] uses Main Mode, Aggressive
Mode, or Quick Mode). It should be stressed that IPsec encryption
without an integrity check is a state of sin.
For many of the MPLS/GMPLS provider's network control messages and
some user requirements, cryptographic authentication of messages
without encryption of the contents of the message may provide
appropriate security. Using IPsec, authentication of messages is
provided by the Authentication Header (AH) or through the use of
the Encapsulating Security Protocol (ESP) with NULL encryption.
Where control messages require integrity but do not use IPsec,
other cryptographic authentication methods are often available.
Message authentication methods currently considered to be secure
are based on hashed message authentication codes (HMAC) [RFC2104]
implemented with a secure hash algorithm such as Secure Hash
Algorithm 1 (SHA-1) [RFC3174]. No attacks against HMAC SHA-1 are
likely to play out in the near future, but it is possible that
people will soon find SHA-1 collisions. Thus, it is important that
mechanisms be designed to be flexible about the choice of hash
functions and message integrity checks. Also, many of these
mechanisms do not include a convenient way to manage and update
keys.
A mechanism to provide a combination of confidentiality, data
origin authentication, and connectionless integrity is the use of
AES in CCM (Counter with CBC-MAC) mode (RFC 4309) [RFC4309], with
an explicit initialization vector (IV), as the IPsec ESP. Recently,
GCM is rapidly replacing CCM as the preferred method: [RFC4103].
5.2.2. MPLS / GMPLS DiffServ and IPsec
MPLS and GMPLS, which provide differentiated services based on
traffic type, may encounter some conflicts with IPsec encryption of
traffic. Because encryption hides the content of the packets, it
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may not be possible to differentiate the encrypted traffic in the
same manner as unencrypted traffic. Although DiffServ markings are
copied to the IPsec header and can provide some differentiation,
not all traffic types can be accommodated by this mechanism. Using
IPsec without IKE or IKEv2 (the better choice) is not advisable.
IKEv2 provides IPsec Security Association creation and management,
entity authentication, key agreement, and key update. It works with
a variety of authentication methods including pre-shared keys,
public key certificates, and EAP. If DoS attacks against IKEv2 are
considered an important threat to mitigate, the cookie-based anti-
spoofing feature of IKEv2 should be used. IKEv2 has its own set of
cryptographic methods, but any of the default suites specified in
[RFC4308] or [RFC4869] provides more than adequate security.
5.2.3. Encryption for device configuration and management
For configuration and management of MPLS/GMPLS devices, encryption
and authentication of the management connection at a level
comparable to that provided by IPsec is desirable.
Several methods of transporting MPLS/GMPLS device management
traffic offer security and confidentiality.
- Secure Shell (SSH) offers protection for TELNET [STD-8] or
terminal-like connections to allow device configuration.
- SNMPv3 [STD62] provides encrypted and authenticated protection
for SNMP-managed devices.
- Transport Layer Security (TLS) [RFC5246] and the closely-related
Secure Sockets Layer (SSL) are widely used for securing HTTP-
based communication, and thus can provide support for most XML-
and SOAP-based device management approaches.
- Since 2004, there has been extensive work proceeding in several
organizations (OASIS, W3C, WS-I, and others) on securing device
management traffic within a "Web Services" framework, using a
wide variety of security models, and providing support for
multiple security token formats, multiple trust domains,
multiple signature formats, and multiple encryption
technologies.
- IPsec provides the services with integrity and confidentiality
at the network layer. With regards to device management, its
current use is primarily focused on in-band management of user-
managed IPsec gateway devices.
- There are recent work in ISMS WG (Integrated Security Model for
SNMP Working Group) to define how to use SSH to secure SNMP, due
to the limited deployment of SNMPv3; and the possibility of
using Kerberos, particularly for interfaces like TELNET, where
client code exists.
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5.2.4. Security Considerations for MPLS Pseudowires
In addition to IP traffic, MPLS networks may be used to transport
other services such as Ethernet, ATM, Frame Relay, and TDM. This is
done by setting up pseudowires (PWs) that tunnel the native service
through the MPLS core by encapsulating at the edges. The PWE
architecture is defined in [RFC3985].
PW tunnels may be set up using the PWE control protocol based on
LDP [RFC4447], and thus security considerations for LDP will most
likely be applicable to the PWE3 control protocol as well.
PW user packets contain at least one MPLS label (the PW label) and
may contain one or more MPLS tunnel labels. After the label stack
there is a four-byte control word (which is optional for some PW
types), followed by the native service payload. It must be
stressed that encapsulation of MPLS PW packets in IP for the
purpose of enabling use of IPsec mechanisms is not a valid option.
The PW client traffic may be secured by use of mechanisms beyond
the scope of this document.
5.2.5. End-to-End versus Hop-by-Hop Protection Tradeoffs
in MPLS/GMPLS
In MPLS/GMPLS, cryptographic protection could potentially be
applied to the MPLS/GMPLS traffic at several different places.
This section discusses some of the tradeoffs in implementing
encryption in several different connection topologies among
different devices within a MPLS/GMPLS network.
Cryptographic protection typically involves a pair of devices that
protect the traffic passing between them. The devices may be
directly connected (over a single "hop"), or intervening devices
may transport the protected traffic between the pair of devices.
The extreme cases involve using protection between every adjacent
pair of devices along a given path (hop-by-hop), or using
protection only between the end devices along a given path (end-to-
end). To keep this discussion within the scope of this document,
the latter ("end-to-end") case considered here is CE-to-CE rather
than fully end-to-end.
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Figure 3 depicts a simplified topology showing the Customer Edge
(CE) devices, the Provider Edge (PE) devices, and a variable number
(three are shown) of Provider core (P) devices, which might be
present along the path between two sites in a single VPN operated
by a single service provider (SP).
Site_1---CE---PE---P---P---P---PE---CE---Site_2
Figure 3: Simplified topology traversing through MPLS/GMPLS core.
Within this simplified topology, and assuming that the P devices
are not involved with cryptographic protection, four basic,
feasible configurations exist for protecting connections among the
devices:
1) Site-to-site (CE-to-CE) - Apply confidentiality or integrity
services between the two CE devices, so that traffic will be
protected throughout the SP's network.
2) Provider edge-to-edge (PE-to-PE) - Apply confidentiality or
integrity services between the two PE devices. Unprotected traffic
is received at one PE from the customer's CE, then it is protected
for transmission through the SP's network to the other PE, and
finally it is decrypted or checked for integrity and sent to the
other CE.
3) Access link (CE-to-PE) - Apply confidentiality or integrity
services between the CE and PE on each side or on only one side.
4) Configurations 2 and 3 above can also be combined, with
confidentiality or integrity running from CE to PE, then PE to PE,
and then PE to CE.
Among the four feasible configurations, key tradeoffs in
considering encryption include:
- Vulnerability to link eavesdropping or tampering - assuming an
attacker can
observe or modify data in transit on the links, would it be
protected by encryption?
- Vulnerability to device compromise - assuming an attacker can get
access to a device (or freely alter its configuration), would the
data be protected?
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- Complexity of device configuration and management - given the
number of sites per VPN customer as Nce and the number of PEs
participating in a given VPN as Npe, how many device configurations
need to be created or maintained, and how do those configurations
scale?
- Processing load on devices - how many cryptographic operations
must be performed given N packets? - This raises considerations of
device capacity and perhaps end-to-end delay.
- Ability of the SP to provide enhanced services (QoS, firewall,
intrusion detection, etc.) - Can the SP inspect the data to provide
these services?
These tradeoffs are discussed for each configuration, below:
1) Site-to-site (CE-to-CE)
Link eavesdropping or tampering - protected on all links
Device compromise - vulnerable to CE compromise
Complexity - single administration, responsible for one device per
site (Nce devices), but overall configuration per VPN scales as
Nce**2.
Though the complexity may be reduced: 1) In practice, as Nce
grows, the number of VPNs falls off from being a full clique;
2) If the CEs run an automated key management protocol, then
they should be able to set up and tear down secured VPNs
without any intervention
Processing load - on each of two CEs, each packet is either
cryptographically processed (2P), though the protection may be
"integrity check only" or "integrity check plus encryption."
Enhanced services - severely limited; typically only Diffserv
markings are visible to the SP, allowing some QoS services
2) Provider edge-to-edge (PE-to-PE)
Link eavesdropping or tampering - vulnerable on CE-PE links;
protected on SP's network links
Device compromise - vulnerable to CE or PE compromise
Complexity - single administration, Npe devices to configure.
(Multiple sites may share a PE device so Npe is typically much
less than Nce.) Scalability of the overall configuration
depends on the PPVPN type: If the cryptographic protection is
separate per VPN context, it scales as Npe**2 per customer VPN.
If it is per-PE, it scales as Npe**2 for all customer VPNs
combined.
Processing load - on each of two PEs, each packet is
cryptographically processed (2P). Note that this 2P is a
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different 2P from case (1), because only PEs are in
consideration here.
Enhanced services - full; SP can apply any enhancements based on
detailed view of traffic
3) Access link (CE-to-PE)
Link eavesdropping or tampering - protected on CE-PE link;
vulnerable on SP's network links
Device compromise - vulnerable to CE or PE compromise
Complexity - two administrations (customer and SP) with device
configuration on each side (Nce + Npe devices to configure) but
because there is no mesh the overall configuration scales as
Nce.
Processing load - on each of two CEs, each packet is
cryptographically processed, plus on each of two PEs, each
packet is cryptographically processed (4P)
Enhanced services - full; SP can apply any enhancements based on
detailed view of traffic
4) Combined Access link and PE-to-PE (essentially hop-by-hop)
Link eavesdropping or tampering - protected on all links
Device compromise - vulnerable to CE or PE compromise
Complexity - two administrations (customer and SP) with device
configuration on each side (Nce + Npe devices to configure).
Scalability of the overall configuration depends on the PPVPN
type: If the cryptographic processing is separate per VPN
context, it scales as Npe**2 per customer VPN. If it is per-
PE, it scales as Npe**2 for all customer VPNs combined.
Processing load - on each of two CEs, each packet is
cryptographically processed, plus on each of two PEs, each
packet is cryptographically processed twice (6P)
Enhanced services - full; SP can apply any enhancements based on
detailed view of traffic
Given the tradeoffs discussed above, a few conclusions can be made:
- Configurations 2 and 3 are subsets of 4 that may be appropriate
alternatives to 4 under certain threat models; the remainder of
these conclusions compare 1 (CE-to-CE) versus 4 (combined access
links and PE-to-PE).
- If protection from link eavesdropping or tampering is all that is
important, then configurations 1 and 4 are equivalent.
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- If protection from device compromise is most important and the
threat is to the CE devices, both cases are equivalent; if the
threat is to the PE devices, configuration 1 is better.
- If reducing complexity is most important, and the size of the
network is small, configuration 1 is better. Otherwise
configuration 4 is better because rather than a mesh of CE devices
it requires a smaller mesh of PE devices. Also, under some PPVPN
approaches the scaling of 4 is further improved by sharing the same
PE-PE mesh across all VPN contexts. The scaling advantage of 4 may
be increased or decreased in any given situation if the CE devices
are simpler to configure than the PE devices, or vice-versa.
- If the overall processing load is a key factor, then 1 is better,
unless the PEs come with a hardware encryption accelerator and the
CEs do not.
- If the availability of enhanced services support from the SP is
most important, then 4 is best.
As a quick overall conclusion, CE-to-CE protection is better
against device compromise, but this comes at the cost of enhanced
services and at the cost of operational complexity due to the
Order(n**2) scaling of a larger mesh.
This analysis of site-to-site vs. hop-by-hop tradeoffs does not
explicitly include cases of multiple providers cooperating to
provide a PPVPN service, public Internet VPN connectivity, or
remote access VPN service, but many of the tradeoffs will be
similar.
In addition to the simplified models, the following should also be
considered:
- There are reasons, perhaps, to protect a specific P-to-P or PE-
to-P.
- There may be reasons to do multiple encryptions over certain
segments. One may be using an encrypted wireless link under our
IPsec VPN to access a SSL-secured web site to download encrypted
email attachments: four layers.)
- It may be that, for example, cryptographic integrity checks are
applied end to end, and confidentiality over a shorter span.
- Different cryptographic protection may be required for control
protocols and data traffic.
- Attention needs to be given to how auxiliary traffic is
protected, e.g., the ICMPv6 packets that flow back during PMTU
discovery, among other examples.
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5.3. Access Control Techniques
Access control techniques include packet-by-packet or packet-flow-
by-packet-flow access control by means of filters and firewalls on
IPv4/IPv6 packets, as well as by means of admitting a "session" for
a control, signaling, or management protocol. Enforcement of access
control by isolated infrastructure addresses is discussed in
another section of this document.
In this document, we distinguish between filtering and firewalls
based primarily on the direction of traffic flow. We define
filtering as being applicable to unidirectional traffic, while a
firewall can analyze and control both sides of a conversation.
The definition has two significant corollaries:
- Routing or traffic flow symmetry: A firewall typically requires
routing symmetry, which is usually enforced by locating a firewall
where the network topology assures that both sides of a
conversation will pass through the firewall. A filter can operate
upon traffic flowing in one direction, without considering traffic
in the reverse direction. Beware that this concept could result in
a single point of failure.
- Statefulness: Because it receives both sides of a conversation, a
firewall may be able to interpret a significant amount of
information concerning the state of that conversation and use this
information to control access. A filter can maintain some limited
state information on a unidirectional flow of packets, but cannot
determine the state of the bi-directional conversation as precisely
as a firewall.
5.3.1. Filtering
It is relatively common for routers to filter data packets. That
is, routers can look for particular values in certain fields of the
IP or higher level (e.g., TCP or UDP) headers. Packets which
matching the criteria associated with a particular filter may
either be discarded or given special treatment. Today, not only
routers, most end hosts today have filters and every instance of
IPsec is also a filter [RFC4301].
In discussing filters, it is useful to separate the Filter
Characteristics that may be used to determine whether a packet
matches a filter from the Packet Actions applied to those packets
which matching a particular filter.
o Filter Characteristics
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Filter characteristics or rules are used to determine whether a
particular packet or set of packets matches a particular filter.
In many cases filter characteristics may be stateless. A stateless
filter determines whether a particular packet matches a filter
based solely on the filter definition, normal forwarding
information (such as the next hop for a packet), and the contents
of that individual packet. Typically stateless filters may consider
the incoming and outgoing logical or physical interface,
information in the IP header, and information in higher layer
headers such as the TCP or UDP header. Information in the IP header
to be considered may for example include source and destination IP
addresses, Protocol field, Fragment Offset, and TOS field in IPv4,
Next Header, Extension Headers, Flow label, etc. in IPv6. Filters
also may consider fields in the TCP or UDP header such as the Port
fields, the SYN field in the TCP header, as well as ICMP and ICMPv6
type.
Stateful filtering maintains packet-specific state information, to
aid in determining whether a filter has been met. For example, a
device might apply stateless filters to the first fragment of a
fragmented IP packet. If the filter matches, then the data unit ID
may be remembered and other fragments of the same packet may then
be considered to match the same filter. Stateful filtering is more
commonly done in firewalls, although firewall technology may be
added to routers. Data unit ID can also be Fragmentation Extension
Header in IPv6.
o Actions based on Filter Results
If a packet, or a series of packets, matches a specific filter,
then a variety of actions which may be taken based on that match.
Examples of such actions include:
- Discard
In many cases, filters are set to catch certain undesirable
packets. Examples may include packets with forged or invalid source
addresses, packets that are part of a DOS or Distributed DoS (DDOS)
attack, or packets which are trying to access unallowed resources
(such as network management packets from an unauthorized source).
Where such filters are activated, it is common to discard the
packet or set of packets matching the filter silently. The
discarded packets may of course also be counted or logged.
- Set CoS
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A filter may be used to set the Class of Service associated with
the packet.
- Count packets or bytes
- Rate Limit
In some cases the set of packets matching a particular filter may
be limited to a specified bandwidth. In this case, packets or bytes
would be counted, and would be forwarded normally up to the
specified limit. Excess packets may be discarded or may be marked
(for example by setting a "discard eligible" bit in the IP ToS
field or the MPLS EXP field).
- Forward and Copy
It is useful in some cases to forward some set of packets normally,
but also to send a copy to a specified other address or interface.
For example, this may be used to implement a lawful intercept
capability or to feed selected packets to an Intrusion Detection
System.
o Other Issues related to Use of Packet Filters
Filtering performance may vary widely according to implementation
and the types and number of rules. Without acceptable performance,
filtering is not useful.
The precise definition of "acceptable" may vary from SP to SP, and
may depend upon the intended use of the filters. For example, for
some uses a filter may be turned on all the time to set CoS, to
prevent an attack, or to mitigate the effect of a possible future
attack. In this case it is likely that the SP will want the filter
to have minimal or no impact on performance. In other cases, a
filter may be turned on only in response to a major attack (such as
a major DDoS attack). In this case a greater performance impact may
be acceptable to some service providers.
A key consideration with the use of packet filters is that they can
provide few options for filtering packets carrying encrypted data.
Because the data itself is not accessible, only packet header
information or other unencrypted fields can be used for filtering.
5.3.2. Firewalls
Firewalls provide a mechanism for control over traffic passing
between different trusted zones in the MPLS/GMPLS model, or between
a trusted zone and an untrusted zone. Firewalls typically provide
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much more functionality than filters, because they may be able to
apply detailed analysis and logical functions to flows, and not
just to individual packets. They may offer a variety of complex
services, such as threshold-driven denial-of-service attack
protection, virus scanning, acting as a TCP connection proxy, etc.
As with other access control techniques, the value of firewalls
depends on a clear understanding of the topologies of the
MPLS/GMPLS core network, the user networks, and the threat model.
Their effectiveness depends on a topology with a clearly defined
inside (secure) and outside (not secure).
Firewalls may be applied to help protect MPLS/GMPLS core network
functions from attacks originating from the Internet or from
MPLS/GMPLS user sites, but typically other defensive techniques
will be used for this purpose.
Where firewalls are employed as a service to protect user VPN sites
from the Internet, different VPN users, and even different sites of
a single VPN user, may have varying firewall requirements. The
overall PPVPN logical and physical topology, along with the
capabilities of the devices implementing the firewall services, has
a significant effect on the feasibility and manageability of such
varied firewall service offerings.
Another consideration with the use of firewalls is that they can
provide few options for handling packets carrying encrypted data.
Because the data itself is not accessible, only packet header
information, other unencrypted fields, or analysis of the flow of
encrypted packets can be used for making decisions on accepting or
rejecting encrypted traffic.
Two approaches are to move the firewall outside of the encrypted
part of the path or to register and pre-approve the encrypted
session with the firewall.
Handling DoS attacks has become increasingly important. Useful
guidelines include the following:
1. Perform ingress filtering everywhere. Upstream prevention is
better.
2. Be able to filter DoS attack packets at line speed.
3. Do not allow oneself to amplify attacks.
4. Continue processing legitimate traffic. Over provide for heavy
loads. Use diverse locations, technologies, etc.
5.3.3. Access Control to management interfaces
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Most of the security issues related to management interfaces can be
addressed through the use of authentication techniques as described
in the section on authentication. However, additional security may
be provided by controlling access to management interfaces in other
ways.
The Optical Internetworking Forum has done good work on protecting
such interfaces with TLS, SSH, Kerberos, IPsec, WSS, etc. See OIF-
SMI-01.0 "Security for Management Interfaces to Network Elements"
[OIF-SMI-01.0], and "Addendum to the Security for Management
Interfaces to Network Elements" [OIF-SMI-02.1]. See also the work
in the ISMS WG.
Management interfaces, especially console ports on MPLS/GMPLS
devices, may be configured so they are only accessible out-of-band,
through a system which is physically or logically separated from
the rest of the MPLS/GMPLS infrastructure.
Where management interfaces are accessible in-band within the
MPLS/GMPLS domain, filtering or firewalling techniques can be used
to restrict unauthorized in-band traffic from having access to
management interfaces. Depending on device capabilities, these
filtering or firewalling techniques can be configured either on
other devices through which the traffic might pass, or on the
individual MPLS/GMPLS devices themselves.
5.4. Use of Isolated Infrastructure
One way to protect the infrastructure used for support of
MPLS/GMPLS is to separate the resources for support of MPLS/GMPLS
services from the resources used for other purposes (such as
support of Internet services). In some cases this may use
physically separate equipment for VPN services, or even a
physically separate network.
For example, PE-based IP VPNs may be run on a separate backbone not
connected to the Internet, or may make use of separate edge routers
from those used to support Internet service. Private IP addresses
(local to the provider and non-routable over the Internet) are
sometimes used to provide additional separation.
In a GMPLS network it is possible to operate the control plane using
physically separate resources form those used for the data plane.
This means that the data plane resources can be physically protected
and isolated from other equipment to protect the data while the
control and management traffic uses network resources that can be
accessed by operators so as to configure the network. Conversely,
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the separation of control and data traffic may lead the operator to
consider that the network is secure because the data plane resources
are physically secure - but this is not the case if the control
plane can be attacked through a shared or open network, and control
plane protection techniques must still be applied.
5.5. Use of Aggregated Infrastructure
In general, it is not feasible to use a completely separate set of
resources for support of each service. In fact, one of the main
reasons for MPLS/GMPLS enabled services is to allow sharing of
resources between multiple services and multiple users. Thus, even
if certain services make use of a separate network from Internet
services, nonetheless there will still be multiple MPLS/GMPLS users
sharing the same network resources. In some cases MPLS/GMPLS
services will share the use of network resources with Internet
services or other services.
It is therefore important for MPLS/GMPLS services to provide
protection between resources used by different parties. Thus a
well-behaved MPLS/GMPLS user should be protected from possible
misbehavior by other users. This requires several security
measurements to be implemented. Resource limits can be placed on
per service and per user basis. For example, using virtual router
or logical router to define hardware or software resource limits
per service or per individual user; using rate limiting per VPN or
per Internet connection to provide bandwidth protection; using
resource reservation for control plane traffic. In addition to
bandwidth protection, separate resource allocation can be used to
limit security attacks only to directly impacted service(s) or
customer(S). Strict, separate, and clearly defined engineering
rules and provisioning procedures can reduce the risks of network
wide impact through control plane attack, DoS attack, or mis-
configurations.
In general, the use of aggregated infrastructure allows the service
provider to benefit from stochastic multiplexing of multiple bursty
flows, and also may in some cases thwart traffic pattern analysis
by combining the data from multiple users. However, service
providers must minimize security risks introduced from any
individual service or individual users.
5.6. Service Provider Quality Control Processes
Deployment of provider-provisioned VPN services in general requires
a relatively large amount of configuration by the SP. For example,
the SP needs to configure which VPN each site belongs to, as well
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as QoS and SLA guarantees. This large amount of required
configuration leads to the possibility of misconfiguration.
It is important for the SP to have operational processes in place
to reduce the potential impact of misconfiguration. CE-to-CE
authentication may also be used to detect misconfiguration when it
occurs.
5.7. Deployment of Testable MPLS/GMPLS Service.
This refers to solutions that can be readily tested to make sure
they are configured correctly. For example, for a point-point
connection, checking that the intended connectivity is working
pretty much ensures that there is not connectivity to some
unintended site.
5.8. Verification of Connectivity
In order to protect against deliberate or accidental misconnection,
mechanisms can be put in place to verify both end-to-end
connectivity and hop-by-hop resources. These mechanisms can trace
the routes of LSPs in both the control plane and the data plane.
It should be noted that where there is an attack on the control
plane it may be that data plane connectivity test mechanisms that
utilize the control plane can also be attacked to hide faults
through false positives, or to disrupt functioning services through
false negatives.
6. Monitoring, Detection, and Reporting of Security Attacks
MPLS/GMPLS network and service may be subject to attacks from a
variety of security threats. Many threats are described in another
part of this document. Many of the defensive techniques described
in this document and elsewhere provide significant levels of
protection from a variety of threats. However, in addition to
silently employing defensive techniques to protect against attacks,
MPLS/GMPLS services can also add value for both providers and
customers by implementing security monitoring systems to detect and
report on any security attacks which occur, regardless of whether
the attacks are effective.
Attackers often begin by probing and analyzing defenses, so systems
that can detect and properly report these early stages of attacks
can provide significant benefits.
Information concerning attack incidents, especially if available
quickly, can be useful in defending against further attacks. It
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can be used to help identify attackers or their specific targets at
an early stage. This knowledge about attackers and targets can be
used to strengthen defenses against specific attacks or attackers,
or improve the defensive services for specific targets on an as-
needed basis. Information collected on attacks may also be useful
in identifying and developing defenses against novel attack types.
Monitoring systems used to detect security attacks in MPLS/GMPLS
typically operate by collecting information from the Provider Edge
(PE), Customer Edge (CE), and/or Provider backbone (P) devices.
Security monitoring systems should have the ability to actively
retrieve information from devices (e.g., SNMP get) or to passively
receive reports from devices (e.g., SNMP notifications). The
specific information exchanged depends on the capabilities of the
devices and on the type of VPN technology. Particular care should
be given to securing the communications channel between the
monitoring systems and the MPLS/GMPLS devices. Syslog WG is
specifying "Logging Capabilities for IP Network Infrastructure".
(The specific references will be made only if the draft(s) became
RFC before this draft.)
The CE, PE, and P devices should employ efficient methods to
acquire and communicate the information needed by the security
monitoring systems. It is important that the communication method
between MPLS/GMPLS devices and security monitoring systems be
designed so that it will not disrupt network operations. As an
example, multiple attack events may be reported through a single
message, rather than allowing each attack event to trigger a
separate message, which might result in a flood of messages,
essentially becoming a denial-of-service attack against the
monitoring system or the network.
The mechanisms for reporting security attacks should be flexible
enough to meet the needs of MPLS/GMPLS service providers,
MPLS/GMPLS customers, and regulatory agencies, if applicable. The
specific reports should depend on the capabilities of the devices,
the security monitoring system, the type of VPN, and the service
level agreements between the provider and customer.
7. Service Provider General Security Requirements
This section covers security requirements the provider may have for
securing its MPLS/GMPLS network infrastructure including LDP and
RSVP-TE specific requirements.
The MPLS/GMPLS service provider's requirements defined here are for
the MPLS/GMPLS core in the reference model. The core network can
be implemented with different types of network technologies, and
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each core network may use different technologies to provide the
various services to users with different levels of offered
security. Therefore, a MPLS/GMPLS service provider may fulfill any
number of the security requirements listed in this section. This
document does not state that a MPLS/GMPLS network must fulfill all
of these requirements to be secure.
These requirements are focused on: 1) how to protect the MPLS/GMPLS
core from various attacks outside the core including network users,
both accidentally and maliciously, 2) how to protect the end users.
7.1. Protection within the Core Network
7.1.1. Control Plane Protection - General
- Protocol authentication within the core:
The network infrastructure must support mechanisms for
authentication of the control plane. If MPLS/GMPLS core is used,
LDP sessions may be authenticated by use TCP MD5, in addition, IGP
and BGP authentication should also be considered. For a core
providing various IP, VPN, or transport services, PE-to-PE
authentication may also be performed via IPsec. See the above
discussion of protocol security services: authentication, integrity
(with replay detection), confidentiality. Protocols need to provide
a complete set of security services from which the SP can choose.
Also, the hard but very important part is key management.
Considerations, Guidelines, and strategies regarding key management
were discussed in [RFC3562], [RFC4107], [RFC4808].
With the cost of authentication coming down rapidly, the
application of control plane authentication may not increase the
cost of implementation for providers significantly, and will help
to improve the security of the core. If the core is dedicated to
MPLS/GMPLS enabled services and without any interconnects to third
parties then this may reduce the requirement for authentication of
the core control plane.
- Infrastructure Hiding
Here we discuss means to hide the provider's infrastructure nodes.
A MPLS/GMPLS provider may make its infrastructure routers (P and PE
routers) unreachable from outside users and unauthorized internal
users. For example, separate address space may be used for the
infrastructure loopbacks.
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Normal TTL propagation may be altered to make the backbone look
like one hop from the outside, but caution needs to be taken for
loop prevention. This prevents the backbone addresses from being
exposed through trace route; however this must also be assessed
against operational requirements for end-to-end fault tracing.
An Internet backbone core may be re-engineered to make Internet
routing an edge function, for example, by using MPLS label
switching for all traffic within the core and possibly make the
Internet a VPN within the PPVPN core itself. This helps to detach
Internet access from PPVPN services.
Separating control plane, data plane, and management plane
functionality in hardware and software may be implemented on the PE
devices to improve security. This may help to limit the problems
when attacked in one particular area, and may allow each plane to
implement additional security measures separately.
PEs are often more vulnerable to attack than P routers, because PEs
cannot be made unreachable from outside users by their very nature.
Access to core trunk resources can be controlled on a per user
basis by using of inbound rate-limiting or traffic shaping; this
can be further enhanced on a per Class of Service basis (see
Section 8.2.3)
In the PE, using separate routing processes for different services,
for example, Internet and PPVPN service, may help to improve the
PPVPN security and better protect VPN customers. Furthermore, if
resources, such as CPU and Memory, can be further separated based
on applications, or even individual VPNs, it may help to provide
improved security and reliability to individual VPN customers.
7.1.2. Control plane protection with RSVP-TE
- General RSVP Security Tools
Isolation of the trusted domain is an important security mechanism
for RSVP, to ensure that an untrusted element cannot access a
router of the trusted domain. However, ASBR-ASBR communication for
inter-AS LSPs needs to be secured specifically. Isolation
mechanisms might also be bypassed by Router Alert IP packets. A
solution could consists of disabling the processing of IP options.
This drops or ignores all IP packets with IP options, including the
router alert option used by RSVP; however, this may have an impact
on other protocols using IP options. An alternative is to configure
access-lists on all incoming interfaces dropping IP protocol 46
(RSVP).
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RSVP security can be strengthened by deactivating RSVP on
interfaces with neighbors who are not authorized to use RSVP, to
protect against adjacent CE-PE attacks. However, this does not
really protect against DoS attacks or attacks on non-adjacent
routers. It has been demonstrated that substantial CPU resources
are consumed simply by processing received RSVP packets, even if
the RSVP process is deactivated for the specific interface on which
the RSVP packets are received.
RSVP neighbor filtering at the protocol level, to restrict the set
of neighbors that can send RSVP messages to a given router,
protects against non-adjacent attacks. However, this does not
protect against DoS attacks and does not effectively protect
against spoofing of the source address of RSVP packets, if the
filter relies on the neighbor's address within the RSVP message.
RSVP neighbor filtering at the data plane level - with an access
list to accept IP packets with port 46, only for specific
neighbors. This requires Router Alert mode to be deactivated and
does not protect against spoofing.
Another valuable tool is RSVP message pacing, to limit the number
of RSVP messages sent to a given neighbor during a given period.
This allows blocking DoS attack propagation.
- limit the impact of an attack on control plane resources
To ensure continued effective operation of the MPLS router even in
the case of an attack that bypasses packet filtering mechanisms
such as Access Control Lists in the data plane, it is important
that routers have some mechanisms to limit the impact of the
attack. There should be a mechanism to rate limit the amount of
control plane traffic addressed to the router, per interface. This
should be configurable on a per-protocol basis, (and, ideally, on a
per-sender basis) to avoid letting an attacked protocol or a given
sender blocking all communications. This requires the ability to
filter and limit the rate of incoming messages of particular
protocols, such as RSVP (filtering at the IP protocol level), and
particular senders. In addition, there should be a mechanism to
limit CPU and memory capacity allocated to RSVP, so as to protect
other control plane elements. To limit the memory allocation, it
will probably be necessary to limit the number of LSPs that can be
set up.
- Authentication for RSVP messages
RSVP message authentication is described in RFC 2747 [RFC2747] and
RFC 3097 [RFC3097]. It is one of the most powerful tools for
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protection against RSVP-based attacks is the use of authentication
for RSVP messages, based on a secure message hash using a key
shared by RSVP neighbors. This protects against LSP creation
attacks, at the expense of consuming significant CPU resources for
digest computation. In addition, if the neighboring RSVP speaker
is compromised, it could be used to launch attacks using
authenticated RSVP messages. These methods, and certain other
aspects of RSVP security, are explained in detail in RFC 4230
[RFC4230]. Key management must be implemented. Logging and auditing
as well as multiple layers of crypto protection can help here.
IPsec can also be used.
One challenge using RSVP message authentication arises in many
cases where non-RSVP nodes are present in the network. In such
cases the RSVP neighbor may not be known up front, thus neighbor
based keying approaches fail, unless the same key is used
everywhere, which is not recommended for security reasons. Group
keying may help in such cases. The security properties of various
keying approaches are discussed in detail in [RSVP-key].
7.1.3. Control plane protection with LDP
The approaches to protect MPLS routers against LDP-based attacks
are similar to those for RSVP, including isolation, protocol
deactivation on specific interfaces, filtering of LDP neighbors at
the protocol level, filtering of LDP neighbors at the data plane
level (access list that filter the TCP & UDP LDP ports),
authentication with message digest, rate limiting of LDP messages
per protocol per sender and limiting all resources allocated to
LDP-related tasks.
7.1.4. Data Plane Protection
IPsec can provide authentication, integrity, confidentiality, and
replay detection for provider or user data. It also has an
associated key management protocol.
In today's MPLS/GMPLS, ATM, or Frame Relay networks, encryption is
not provided as a basic feature. Mechanisms described in section 5
can be used to secure the MPLS data plane traffic carried over MPLS
core. Both the Frame Relay Forum and the ATM Forum standardized
cryptographic security services in the late 1990s, but these
standards are not widely implemented.
7.2. Protection on the User Access Link
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Peer or neighbor protocol authentication may be used to enhance
security. For example, BGP MD5 authentication may be used to
enhance security on PE-CE links using eBGP. In the case of Inter-
provider connection, cryptographic protection mechanisms between
ASes, such as IPsec, may be used.
If multiple services are provided on the same PE platform,
different WAN address spaces may be used for different services
(e.g., VPN and non-VPN) to enhance isolation.
Firewall and Filtering: access control mechanisms can be used to
filter any packets destined for the service provider's
infrastructure prefix or eliminate routes identified as
illegitimate.
Rate limiting may be applied to the user interface/logical
interfaces against DDoS bandwidth attack. This is helpful when the
PE device is supporting both multi-services, especially VPN and
Internet Services, on the same physical interfaces through
different logical interfaces.
7.2.1. Link Authentication
Authentication can be used to validate site access to the network
via fixed or logical connections, e.g. L2TP, IPsec, respectively.
If the user wishes to hold the authentication credentials for
access, then provider solutions require the flexibility for either
direct authentication by the PE itself or interaction with a
customer authentication server. Mechanisms are required in the
latter case to ensure that the interaction between the PE and the
customer authentication server is appropriately secured.
7.2.2. Access Routing Control
Routing protocol level e.g., RIP, OSPF, or BGP, may be used to
provide control access between a CE and PE. Per neighbor and per
VPN routing policies may be established to enhance security and
reduce the impact of a malicious or non-malicious attack on the PE;
the following mechanisms, in particular, should be considered:
- Limiting the number of prefixes that may be advertised on
a per access basis into the PE. Appropriate action may be
taken should a limit be exceeded, e.g., the PE shutting
down the peer session to the CE
- Applying route dampening at the PE on received routing
updates
- Definition of a per VPN prefix limit after which
additional prefixes will not be added to the VPN routing
table.
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In the case of Inter-provider connection, access protection, link
authentication, and routing policies as described above may be
applied. Both inbound and outbound firewall or filtering mechanism
between ASes may be applied. Proper security procedures must be
implemented in Inter-provider interconnection to protect the
providers' network infrastructure and their customers. This may be
custom designed for each Inter-Provider peering connection, and
must be agreed upon by both providers.
7.2.3. Access QoS
MPLS/GMPLS providers offering QoS-enabled services require
mechanisms to ensure that individual accesses are validated against
their subscribed QOS profile and as such gain access to core
resources that match their service profile. Mechanisms such as per
Class of Service rate limiting or traffic shaping on ingress to the
MPLS/GMPLS core are one option for providing this level of control.
Such mechanisms may require the per Class of Service profile to be
enforced either by marking, or remarking or discard of traffic
outside of the profile.
7.2.4. Customer service monitoring tools
End users requiring specific statistics on the core, e.g., routing
table, interface status, or QoS statistics, requirements for
mechanisms at the PE both to validate the incoming user and limit
the views available to that particular user. Mechanisms should
also be considered to ensure that such access cannot be used a
means of a DoS attack (either malicious or accidental) on the PE
itself. This could be accomplished through either separation of
these resources within the PE itself or via the capability to rate-
limit on a per physical or logical connection basis such traffic.
7.3. General User Requirements for MPLS/GMPLS Providers
MPLS/GMPLS providers must support end users' security requirements.
Depending on the technologies used, these requirements may include:
- User control plane separation - routing isolation when
applicable, for example, in the case of MPLS VPNs.
- Protection against intrusion, DoS attacks and spoofing
- Access Authentication
- Techniques highlighted through this document that identify
methodologies for the protection of resources and the
MPLS/GMPLS infrastructure.
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Hardware or software errors in equipment leading to breaches in
security are not within the scope of this document.
8. Inter-provider Security Requirements
This section discusses security capabilities that are important at
the MPLS/GMPLS Inter-provider connections and at devices (including
ASBR routers) supporting these connections. The security
capabilities stated in this section should be considered as
complementary to security considerations addressed in individual
protocol specifications or security frameworks.
Security vulnerabilities and exposures may be propagated across
multiple networks because of security vulnerabilities arising in
one peer's network. Threats to security originate from accidental,
administrative, and intentional sources. Intentional threats
include events such as spoofing and Denial of Service (DoS)
attacks.
The level and nature of threats, as well as security and
availability requirements, may vary over time and from network to
network. This section therefore discusses capabilities that need to
be available in equipment deployed for support of the MPLS
InterCarrier Interconnect (MPLS-ICI). Whether any particular
capability is used in any one specific instance of the ICI is up to
the service providers managing the PE equipment offering/using the
ICI services.
8.1. Control Plane Protection
This section discusses capabilities for control plane protection,
including protection of routing, signaling, and OAM capabilities.
8.1.1. Authentication of Signaling Sessions
Authentication may be needed for signaling sessions (i.e., BGP, LDP
and RSVP-TE) and routing sessions (e.g., BGP) as well as OAM
sessions across domain boundaries. Equipment must be able to
support exchange of all protocol messages over IPsec, with NULL
encryption and authentication, between the peering ASBRs. Support
for message authentication for LDP, BGP and RSVP-TE authentication
must also be provided. Manual keying of IPsec should not be used.
IKEv2 with pre-shared secrets or public key methods should be used.
Replay detection should be used.
Mechanisms to authenticate and validate a dynamic setup request
MUST be available. For instance, if dynamic signaling of a TE-LSP
or PW is crossing a domain boundary, there must be a way to detect
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whether the LSP source is who it claims to be and that he is
allowed to connect to the destination.
Message authentication support for all TCP-based protocols within
the scope of the MPLS-ICI (i.e., LDP signaling and BGP routing) and
Message authentication with the RSVP-TE Integrity Object MUST be
provided to interoperate with current practices.
Equipment SHOULD be able to support exchange of all signaling and
routing (LDP, RSVP-TE, and BGP) protocol messages over a single
IPSec security association pair in tunnel or transport mode with
authentication but with NULL encryption, between the peering ASBRs.
IPSec, if supported, must be supported with HMAC-MD5 and optionally
SHA-1. It is expected that authentication algorithms will evolve
over time and support can be updated as needed.
OAM Operations across the MPLS-ICI could also be the source of
security threats on the provider infrastructure as well as the
service offered over the MPLS-ICI. A large volume of OAM messages
could overwhelm the processing capabilities of an ASBR if the ASBR
is not properly protected. Maliciously generated OAM messages could
also be used to bring down an otherwise healthy service (e.g., MPLS
Pseudo Wire), and therefore affect service security. MPLS-ping does
not support authentication today, and that support should be
subject for future considerations. Bidirectional Forwarding
Detection (BFD), however, does have support for carrying an
authentication object. It also supports Time-To-Live (TTL)
processing as an anti-replay measure. Implementations conformant
with this MPLS-ICI should support BFD authentication using MD5 and
must support the procedures for TTL processing.
8.1.2. Protection against DoS attacks in the Control
Plane
Implementation must have the ability to prevent signaling and
routing DoS attacks on the control plane per interface and
provider. Such prevention may be provided by rate-limiting
signaling and routing messages that can be sent by a peer provider
according to a traffic profile and by guarding against malformed
packets.
Equipment MUST provide the ability to filter signaling, routing,
and OAM packets destined for the device, and MUST provide the
ability to rate limit such packets. Packet filters SHOULD be
capable of being separately applied per interface, and SHOULD have
minimal or no performance impact. For example, this allows an
operator to filter or rate-limit signaling, routing, and OAM
messages that can be sent by a peer provider and limit such traffic
to a given profile.
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During a control plane DoS attack against an ASBR, the router
SHOULD guarantee sufficient resources to allow network operators to
execute network management commands to take corrective action, such
as turning on additional filters or disconnecting an interface
under attack. DoS attacks on the control plane SHOULD NOT adversely
affect data plane performance.
Equipment running BGP MUST support the ability to limit the number
of BGP routes received from any particular peer. Furthermore, in
the case of IPVPN, a router MUST be able to limit the number of
routes learned from a BGP peer per IPVPN. In the case that a device
has multiple BGP peers, it SHOULD be possible for the limit to vary
between peers.
8.1.3. Protection against Malformed Packets
Equipment SHOULD be robust in the presence of malformed protocol
packets. For example, malformed routing, signaling, and OAM packets
should be treated in accordance to the relevant protocol
specification.
8.1.4. Ability to Enable/Disable Specific Protocols
Ability to drop any signaling or routing protocol messages when
these messages are to be processed by the ASBR but the
corresponding protocol is not enabled on that interface.
Equipment must allow an administrator to enable or disable a
protocol (default protocol is disabled unless administratively
enable) on an interface basis.
Equipment MUST be able to drop any signaling or routing protocol
messages when these messages are to be processed by the ASBR but
the corresponding protocol is not enabled on that interface. This
dropping SHOULD NOT adversely affect data plane or control plane
performance.
8.1.5. Protection Against Incorrect Cross Connection
The capability of detecting and locating faults in a LSP cross-
connect MUST be provided. Such faults may cause security violations
as they result in directing traffic to the wrong destinations. This
capability may rely on OAM functions. Equipment MUST support MPLS
LSP ping [RFC4379]. This MAY be used to verify end to end
connectivity for the LSP (e.g., PW, TE Tunnel, VPN LSP, etc.), and
to verify PE-to-PE connectivity for IP VPN services.
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When routing information is advertised from one domain to the
other, operators must be able to guard against situations that
result in traffic hijacking, black-holing, resource stealing (e.g.,
number of routes), etc. For instance, in the IPVPN case, an
operator must be able to block routes based on associated route
target attributes. In addition, mechanisms must exist to verify
whether a route advertised by a peer for a given VPN is actually a
valid route and whether the VPN has a site attached or reachable
through that domain.
Equipment (ASBRs and Route Reflectors (RRs)) supporting operation
of BGP MUST be able to restrict which Route Target attributes are
sent to and accepted from a BGP peer across an ICI. Equipment
(ASBRs, RRs) SHOULD also be able to inform the peer regarding which
Route Target attributes it will accept from a peer, because sending
an incorrect Route Target can result in incorrect cross-connection
of VPNs. Also, sending inappropriate route targets to a peer may
disclose confidential information.
8.1.6. Protection Against Spoofed Updates and Route
Advertisements
Equipment MUST support route filtering of routes received via a BGP
peer sessions by applying policies that include one or more the
following: AS path, BGP next hop, standard community or extended
community.
8.1.7. Protection of Confidential Information
Ability to identify and block messages with confidential
information from leaving the trusted domain that can reveal
confidential information about network operation (e.g., performance
OAM messages or MPLS-ping messages) is required. Service Providers
must have the flexibility of handling these messages at the ASBR.
Equipment SHOULD provide the ability to identify and restrict where
it sends messages or that can reveal confidential information about
network operation (e.g., performance OAM messages, LSP Traceroute
messages). Service Providers must have the flexibility of handling
these messages at the ASBR. For example, equipment supporting LSP
Traceroute MAY limit to which addresses replies can be sent.
Note: This capability should be used with care. For example, if a
service provider chooses to prohibit the exchange of LSP ping
messages at the ICI, it may make it more difficult to debug
incorrect cross-connection of LSPs or other problems.
A provider may decide to progress these messages if they are
incoming from a trusted provider and are targeted to specific
agreed-on addresses. Another provider may decide to traffic police,
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reject, or apply policies to these messages. Solutions must enable
providers to control the information that is relayed to another
provider about the path that a LSP takes. For example, in RSVP-TE
record route object or MPLS-ping trace, a provider must be able to
control the information contained in corresponding messages when
sent to another provider.
8.1.8. Protection Against over-provisioned number of
RSVP-TE LSPs and bandwidth reservation
In addition to the control plane protection mechanisms listed in
the previous section on Control plane protection with RSVP-TE, the
ASBR must be able both to limit the number of LSPs that can be set
up by other domains and to limit the amount of bandwidth that can
be reserved. A provider's ASBR may deny a LSP set up request or a
bandwidth reservation request sent by another provider's whose the
limits have been reached.
8.2. Data Plane Protection
8.2.1. Protection against DoS in the Data Plane
This is described earlier in this document.
8.2.2. Protection against Label Spoofing
Verification that a label received across an interconnect was
actually assigned to the provider across the interconnect. If the
label was not assigned to the provider, the packet MUST be dropped.
Equipment MUST be able to verify that a label received across an
interconnect was actually assigned to a LSP arriving from the
provider across that interconnect. If the label was not assigned to
a LSP which arrives at this router from the correct neighboring
provider, the packet MUST be dropped. This verification can be
applied to the top label only. The top label is the received top
label and every label that is exposed by label popping to be used
for forwarding decisions.
Equipment MUST provide the capability of dropping MPLS-labeled
packets if all labels in the stack are not processed. This lets
carriers guarantee that every label that enters its domain from
another carrier was actually assigned to that carrier.
The following requirements are not directly reflected in this
document but must be used as guidance for addressing further work.
Solutions MUST NOT force operators to reveal reachability
information to routers within their domains. <note: It is believed
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that this requirement is met via other requirements specified in
this section plus the normal operation of IP routing, which does
not reveal individual hosts.>
Mechanisms to authenticate and validate a dynamic setup request
MUST be available. For instance, if dynamic signaling of a TE-LSP
or PW is crossing a domain boundary, there must be a way to detect
whether the LSP source is who it claims to be and that he is
allowed to connect to the destination.
8.2.3. Protection using ingress traffic policing and
enforcement
The following simple diagram illustrates a potential security issue
on the data plane issue across a MPLS interconnect:
SP2 - ASBR2 - labeled path - ASBR1 - P1 - SP1's PSN - P2 - PE1
| | | |
|< AS2 >|<MPLS interconnect>|< AS1 >|
Traffic flow direction is from SP2 to SP1
In the case of down stream label assignment, the transit label used
by ASBR2 is allocated by ASBR1, which in turn advertises it to
ASB2 (downstream unsolicited or on-demand), and this label is used
for a service context (VPN label, PW VC label, etc.), and this LSP
is normally terminated at a forwarding table belonging to the
service instance on PE (PE1) in SP1.
In the example above, ASBR1 would not know whether the label of an
incoming packet from ASBR2 over the interconnect is a VPN label or
PSN label for AS1. So it is possible (though rare) that ASBR2 can
be accidentally or intentionally configured such that the incoming
label could match a PSN label (e.g., LDP) in AS1. Then, this LSP
would end up on the global plane of an infrastructure router (P or
PE1), and this could invite a unidirectional attack on that P or
PE1 where the LSP terminates.
To mitigate this threat, implementations SHOULD be able to do a
forwarding path look-up for the label on an incoming packet from an
interconnect in a Label Forwarding Information Base (LFIB) space
that is only intended for its own service context or provide a
mechanism on the data plane that would ensure the incoming labels
are what ASBR1 has allocated and advertised.
A similar concept has been proposed in "Requirements for Multi-
Segment Pseudowire Emulation Edge-to-Edge (PWE3)" [RFC5254].
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When using upstream label assignment, the upstream source must be
identified and authenticated so the labels can be accepted as from
trusted source.
9. Summary of MPLS and GMPLS Security
The following summary provides a quick check list of MPLS and GMPLS
security threats, defense techniques, and the best practice guide
outlines for MPLS and GMPLS deployment.
9.1. MPLS and GMPLS Specific Security Threats
9.1.1. Control plane attacks
Types of attacks on the control plane:
- Unauthorized LSP creation
- LSP message interception
Attacks against RSVP-TE: DoS attack with setting up
unauthorized LSP and/or LSP messages.
Attacks against LDP: DoS attack with storms of LDP Hello
messages or LDP TCP Syn messages.
Attacks may be launched from external or internal sources, or
through SP management systems.
Attacks may be targeted to the SP routing protocols or
infrastructure elements.
In general, control protocols may be attacked by:
- MPLS signaling (LDP, RSVP-TE)
- PCE signaling
- IPsec signaling (IKE and IKEv2)
- ICMP and ICMPv6
- L2TP
- BGP-based membership discovery
- Database-based membership discovery (e.g., RADIUS)
- OAM and diagnostic protocol such as MPLS-ping and LMP
- Other protocols that may be important to the control
infrastructure, e.g., DNS, LMP, NTP, SNMP, and GRE.
9.1.2. Data plane attacks
- Unauthorized observation of data traffic
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- Data traffic modification
- Spoofing and replay
- Unauthorized Deletion
- Unauthorized Traffic Pattern Analysis
- Denial of Service Attacks
9.2. Defense Techniques
1) Authentication:
- Identity authentication - Key management
- Management System Authentication
- Peer-to-peer authentication
2) Cryptographic techniques
3) Use of IPsec in MPLS/GMPLS networks
4) Encryption for device configuration and management
5) Cryptographic Techniques for MPLS Pseudowires
6) End-to-End versus Hop-by-Hop Protection (CE-CE, PE-PE, PE-CE)
7) Access Control techniques
- Filtering
- Firewalls
- Access Control to management interfaces
8) Infrastructure isolation
9) Use of aggregation infrastructure
10) Quality Control Processes
11) Testable MPLS/GMPLS Service
12) End-to-end connectivity verification techniques
13) Hop-by-hop resource configuration verification and discovery
techniques
9.3. Service Provider MPLS and GMPLS Best Practice Outlines
9.3.1. SP infrastructure protection
1) General control plane protection
- Protocol authentication within the core
- Infrastructure Hiding (e.g. disable TTL propagation)
2) RSVP control plane protection
- Using RSVP security tools
- Isolation of the trusted domain
- Deactivating RSVP on interfaces with neighbors who are not
authorized to use RSVP
- RSVP neighbor filtering at the protocol level and data plane
level
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- Authentication for RSVP messages
- RSVP message pacing
3) LDP control plane protection (similar techniques as for RSVP)
4) Data plane protection
- User Access link protection
- Link Authentication
- Access routing control (e.g. prefix limits, route dampening,
routing table limits (e.g. VRF limits)
- Access QoS control
- Using customer service monitoring tools
- Use of MPLS-ping (with its own control plane security) to
verify end-to-end connectivity of MPLS LSPs
- LMP (with its own security) to verify hop-by-hop
connectivity
9.3.2. Inter-provider Security
Inter-provider connections are high security risk areas. Similar
techniques and procedures as described in for SP general core
protection are listed below for inter-provider connections.
1) Control plane protection at the inter-provider connections
- Authentication of Signaling Sessions
- Protection against DoS attacks in the Control Plane
- Protection against Malformed Packets
- Ability to Enable/Disable Specific Protocols
- Protection Against Incorrect Cross Connection
- Protection Against Spoofed Updates and Route Advertisements
- Protection of Confidential Information
- Protection Against over-provisioned number of RSVP-TE LSPs
and bandwidth reservation
2) Data Plane Protection at the inter-provider connections
- Protection against DoS in the Data Plane
- Protection against Label Spoofing
10. Security Considerations
Security considerations constitute the sole subject of this memo
and hence are discussed throughout. Here we recap what has been
presented and explain at a high level the role of each type of
consideration in an overall secure MPLS/GMPLS system.
The document describes a number of potential security threats.
Some of these threats have already been observed occurring in
running networks; others are largely theoretical at this time.
Fang, et al. Informational [Page 51]
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DoS attacks and intrusion attacks from the Internet against service
providers' infrastructure have been seen. DoS "attacks" (typically
not malicious) have also been seen in which CE equipment overwhelms
PE equipment with high quantities or rates of packet traffic or
routing information. Operational or provisioning errors are cited
by service providers as one of their prime concerns.
The document describes a variety of defensive techniques that may
be used to counter the suspected threats. All of the techniques
presented involve mature and widely implemented technologies that
are practical to implement.
The document describes the importance of detecting, monitoring, and
reporting attacks, both successful and unsuccessful. These
activities are essential for "understanding one's enemy",
mobilizing new defenses, and obtaining metrics about how secure the
MPLS/GMPLS network is. As such, they are vital components of any
complete PPVPN security system.
The document evaluates MPLS/GMPLS security requirements from a
customer's perspective as well as from a service provider's
perspective. These sections re-evaluate the identified threats
from the perspectives of the various stakeholders and are meant to
assist equipment vendors and service providers, who must ultimately
decide what threats to protect against in any given configuration
or service offering.
11. IANA Considerations
No new IANA considerations.
12. Normative References
[RFC2747] F. Baker, et al., "RSVP Cryptographic Authentication",
EFC 2741, January 2000.
[RFC3031] E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label
Switching Architecture", RFC 3031, January 2001.
[RFC3097] R. Braden and L. Zhang, "RSVP Cryptographic
Authentication - Updated Message Type Value", RFC 3097, April 2001.
[RFC3945] E. Mannie, "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
Fang, et al. Informational [Page 52]
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[RFC3209] Awduche, et al., "RSVP-TE: Extensions to RSVP for LSP
Tunnels", December 2001.
[RFC4301] S. Kent, K. Seo, "Security Architecture for the Internet
Protocol," December 2005.
[RFC4302] S. Kent, "IP Authentication Header," December 2005.
[RFC4835] V. Manral, "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", April 2007.
[RFC4306] C. Kaufman, "Internet Key Exchange (IKEv2)
Protocol",December 2005.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES)
CCM Mode with IPsec Encapsulating Security Payload (ESP)", December
2005.
[RFC5246] T. Dierks and E. Rescorla, "The Transport Layer Security
(TLS) Protocol, Version 1.2," August 2008.
[RFC4379] K. Kompella and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", February 2006.
[RFC4447] Martini, et al., "Pseudowire Setup and Maintenance Using
the Label Distribution Protocol (LDP)", April 2006.
[RFC5036] Andersson, et al., "LDP Specification", October 2007.
[STD62] "Simple Network Management Protocol, Version 3,", December
2002.
[STD-8] J. Postel and J. Reynolds, "TELNET Protocol Specification",
STD 8, May 1983.
13. Informational References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
[OIF-SMI-01.0] Renee Esposito, "Security for Management Interfaces
to Network Elements", Optical Internetworking Forum, Sept. 2003.
Fang, et al. Informational [Page 53]
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[OIF-SMI-02.1] Renee Esposito, "Addendum to the Security for
Management Interfaces to Network Elements", Optical Internetworking
Forum, March 2006.
[RFC2104] H. Krawczyk, M. Bellare, R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication," February 1997.
[RFC2411] R. Thayer, N. Doraswamy, R. Glenn, "IP Security Document
Roadmap," November 1998.
[RFC3174] D. Eastlake, 3rd, and P. Jones, "US Secure Hash Algorithm
1 (SHA1)," September 2001.
[RFC3562] M. Leech, "Key Management Considerations for the TCP MD5
Signature Option", July 2003.
[RFC3631] S. Bellovin, C. Kaufman, J. Schiller, "Security
Mechanisms for the Internet," December 2003.
[RFC3985] S. Bryant and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", March 2005.
[RFC4103] G. Hellstrom and P. Jones, "RTP Payload for Text
Conversation", June 2005.
[RFC4107] S. Bellovin, R. Housley, "Guidelines for Cryptographic
Key Management", June 2005.
[RFC4110] R. Callon and M. Suzuki, "A Framework for Layer 3
Provider-Provisioned Virtual Private Networks (PPVPNs)", July 2005.
[RFC4111] L. Fang, "Security Framework of Provider Provisioned
VPN", RFC 4111, July 2005.
[RFC4230] H. Tschofenig and R. Graveman, "RSVP Security
Properties", December 2005.
[RFC4308] P. Hoffman, "Cryptographic Suites for IPsec", December
2005.
[RFC4593] A. Barbir, S. Murphy, Y. Yang, "Generic Threats to Routing
Protocols", October 2006.
[RFC4808] S. Bellovin, "Key Change Strategies for TCP-MD5", March
2007.
[RFC4869] L. Law and J. Solinas, "Suite B Cryptographic Suites for
IPsec", April 2007.
Fang, et al. Informational [Page 54]
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[RFC5254] N. Bitar, M. Bocci, L. Martini, "Requirements for Multi-
Segment Pseudowire Emulation Edge-to-Edge (PWE3)", October 2008.
[MFA MPLS ICI] N. Bitar, "MPLS InterCarrier Interconnect Technical
Specification", IP/MPLS Forum 19.0.0, April 2008.
[opsec efforts] C. Lonvick and D. Spak, "Security Best Practices
Efforts and Documents", draft-ietf-opsec-efforts-08.txt, June 2008.
[RSVP-key] M. Behringer, F. Le Faucheur, "Applicability of Keying
Methods for RSVP Security", draft-ietf-tsvwg-rsvp-security-
groupkeying-01.txt, July 2008
14. Author's Addresses
Luyuan Fang
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough, MA 01719
USA
Email: lufang@cisco.com
Michael Behringer
Cisco Systems, Inc.
Village d'Entreprises Green Side
400, Avenue Roumanille, Batiment T 3
06410 Biot, Sophia Antipolis
FRANCE
Email: mbehring@cisco.com
Ross Callon
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
USA
Email: rcallon@juniper.net
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Fang, et al. Informational [Page 55]
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Email: jeanlouis.leroux@francetelecom.com
Raymond Zhang
British Telecom
2160 E. Grand Ave. El Segundo, CA 90025
USA
Email: raymond.zhang@bt.com
Paul Knight
Nortel
600 Technology Park Drive
Billerica, MA 01821
Email: paul.knight@nortel.com
Yaakov (Jonathan) Stein
RAD Data Communications
24 Raoul Wallenberg St., Bldg C
Tel Aviv 69719
ISRAEL
Email: yaakov_s@rad.com
Nabil Bitar
Verizon
40 Sylvan Road
Waltham, MA 02145
Email: nabil.bitar@verizon.com
Richard Graveman
RFG Security
15 Park Avenue
Morristown, NJ 07960
Email: rfg@acm.org
Monique Morrow
Glatt-com
CH-8301 Glattzentrum
Switzerland
Email: mmorrow@cisco.com
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Fang, et al. Informational [Page 56]
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15. Acknowledgements
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Fang, et al. Informational [Page 57]
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The authors and contributors would also like to acknowledge the
helpful comments and suggestions from Sam Hartman, Dimitri
Papadimitriou, Kannan Varadhan, Stephen Farrell, and Scott Brim in
particular for his comments and discussion through GEN-ART review.
Fang, et al. Informational [Page 58]