PANA Working Group
Internet Draft M. Parthasarathy
Document: draft-ietf-pana-ipsec-07.txt Nokia
Expires: January 2006 July 2005
PANA Enabling IPsec based Access Control
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Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract
PANA (Protocol for carrying Authentication for Network Access) is a
protocol for authenticating clients to the access network using IP
based protocols. The PANA protocol authenticates the client and also
establishes a PANA security association between the PANA client and
PANA authentication agent at the end of a successful authentication.
This document discusses the details for establishing an IPsec
security association using the PANA security association for enabling
IPsec based access control.
Table of Contents
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1.0 Introduction..................................................2
2.0 Keywords......................................................4
3.0 Pre-requisites for IPsec SA establishment.....................4
4.0 IP Address Configuration......................................4
5.0 IKE Pre-shared key derivation.................................5
6.0 IKE and IPsec details.........................................6
7.0 Packet Formats................................................7
8.0 IPsec SPD entries.............................................8
9.0 Dual Stack Operation.........................................11
10.0 IANA Considerations.........................................12
10.0 Security considerations.....................................12
11.0 Normative References........................................12
12.0 Informative References......................................12
13.0 Acknowledgments.............................................14
14.0 Revision log................................................14
15.0 Appendix A..................................................15
16.0 Author's Addresses..........................................16
Intellectual Property Statement..................................16
Disclaimer of Validity...........................................17
Copyright Statement..............................................17
Acknowledgment...................................................17
1.0 Introduction
PANA (Protocol for carrying Authentication for Network Access) is a
protocol [PANA-PROT] for authenticating clients to the access network
using IP based protocols. The PANA protocol authenticates the client
and also establishes a PANA security association between the PANA
client (PaC) and PANA authentication agent (PAA) at the end of
successful authentication. The PAA indicates the results of the
authentication using the PANA-Bind-Request message wherein it can
indicate the access control method enforced by the access network.
The PANA protocol [PANA-PROT] does not discuss any details of IPsec
[RFC2401] security association (SA) establishment, when IPsec is used
for access control. This document discusses the details of
establishing an IPsec security association between the PANA client
and the enforcement point. The IPsec SA is established using IKE
[RFC2409], which in turn uses the pre-shared key derived from the EAP
authentication. The IPsec SA used to protect the packet provides the
assurance that the packet comes from the client that authenticated to
the network. Thus, the IPsec SA can be used for access control and
specifically used to prevent the service theft mentioned in
[RFC4016]. The term "access control" in this document refers to the
per-packet authentication provided by IPsec. IPsec is used to protect
packets flowing between PaC and EP in both directions.
Please refer to [PANAREQ] for terminology and definitions of terms
used in this document. The PANA framework document [PANA-FRAME]
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describes the deployment scenarios for IPsec. The following picture
illustrates what is being protected with IPsec. The different
scenarios of PANA usage are described in the [PANAREQ]. When IPsec is
used, scenarios 3 and 5 are supported as shown below. As shown in
Figure 1, the Enforcement Point (EP), Access Router (AR) and the PANA
authentication agent are co-located which is described as scenario 3
in [PANAREQ].
PaC ------------+
|
+---EP/AR/PAA----Intranet/Internet
|
PaC ------------+
<-------IPsec------>
Figure 1: PAA/EP/AR are co-located
As show in Figure 2, only the AR and EP are co-located. The PAA is a
separate node though located on the same link as the AR and EP. All
of them are one IP hop away from the PaC. This is the same as
scenario 5 described in [PANAREQ].
PaC -------------+
|
+---PAA
|
+---EP/AR-----Intranet/Internet
|
PaC -------------+
<------IPsec----->
Figure 2: EP and AR are co-located
The IPsec security association protects the traffic between the PaC
and EP. In IPsec terms, the EP is a security gateway (therefore a
router) and forwards packets coming from the PaC to other nodes.
First, this document discusses some of the pre-requisites for IPsec
SA establishment. Next, it gives details on what should be
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communicated between the PAA and EP. Then, it gives the details of
IKE exchange with IPsec packet formats and SPD entries. Finally, it
discusses the dual stack operation.
2.0 Keywords
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 [RFC2118].
3.0 Pre-requisites for IPsec SA establishment
This document assumes that the following have already happened before
the IKE exchange starts.
1) The PaC) and PAA mutually authenticate each other using an EAP
method that is able to derive a AAA-key [EAP-KEY].
2) The PaC learns the IP address of the Enforcement point (EP)
during the PANA exchange.
3) The PaC learns that the network uses IPsec [RFC2401] for
securing the link between the PaC and EP during the PANA
exchange.
4.0 IP Address Configuration
The IP address configuration is explained in [PANA-FRAME]. Some of
the details relevant to IPsec are briefly repeated here for clarity.
The PaC configures an IP address before the PANA protocol exchange
begins. This address is called a pre-PANA address (PRPA). After a
successful authentication, the client may have to configure a post-
PANA address (POPA) for communication with other nodes, if PRPA is a
local-use (e.g., link-local or private address) or a temporarily
allocated IP address.
The PRPA of the PaC may be a link-local address [IPV4-LINK] or a
private address [RFC1918] or a routable address or an IPv6 link-local
address or global address [RFC2462]. Please refer to [PANA-FRAME] for
more details on how these addresses may be configured. The PaC would
use the PRPA as the outer address of IPsec tunnel mode SA (IPsec-
TOA). The PaC also needs to configure an inner address (IPsec-TIA).
There are different ways to configure IPsec-TIA.
1) Some IPv4 IPsec implementations are known to work properly when
the same address is configured as both the IPsec-TIA and IPsec-
TOA. When PRPA is a routable address, the PRPA may be used as
both the IPsec-TIA and IPsec-TOA and POPA may not be configured.
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2) In IPv4, an IPsec-TIA can be obtained via the configuration
method available using DHCP over IPsec tunnels [RFC3456]. The
minor difference from the original usage of [RFC3456] is that
the IPsec-TOA does not need to be a routable address when
[RFC3456] is used between the PaC and EP.
3) When IKEv2 [IKEV2] is used for security association negotiation,
the address configuration method available in [IKEV2] can be
used for configuring the IPsec-TIA for both IPv4 and IPv6.
There are other address configuration methods possible. They have
some implementation issues, which are described in the Appendix A.
5.0 IKE Pre-shared key derivation
If the network chooses IPsec to secure the link between the PaC and
EP, the PAA should communicate the IKE pre-shared key (Pac-EP Master
Key), Key-Id, the device identifier of the PaC, and the session-Id to
the EP before the IKE exchange begins. Whenever the IKE pre-shared
key changes due to re-authentication as described below, the new
value is computed by the PAA and communicated to the EP with all the
other parameters.
The IKE exchange between the PaC and PAA is equivalent to the 4-way
handshake in [IEEE80211i] following the EAP exchange. The IKE
exchange establishes the IPsec SA similar to the pair-wise transient
key (PTK) established in [IEEE80211i]. The IKE exchange provides both
key confirmation and protected cipher-suite negotiation.
The IKE pre-shared key is derived as follows (where "|" means
concactenation).
IKE Pre-shared Key = HMAC-SHA-1 (PaC-EP-Master-Key,
"IKE-preshared key" |
Session ID | Key-ID | EP-address)
The values have the following meaning:
PaC-EP-Master-Key: A key derived from the AAA-key for each EP as
defined in [PANA-PROT].
Session ID: The value as defined in the PANA protocol [PANA-PROT],
identifies a particular session of a client.
Key-ID: This identifies the PaC-EP-Master-Key within a given session
[PANA-PROT]. During the lifetime of the PANA session, there could be
multiple runs of EAP re-authentications. As EAP re-authentication
changes the AAA-key which in turn affects Pac-EP-Master-Key, Key-ID
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is used to identify the right PaC-EP-Master-Key. This is contained in
the Key-ID AVP [PANA-PROT].
EP-address: This is the address of the enforcement point with which
the IKE exchange is being performed. When the PAA is controlling
multiple EPs, this provides a different pre-shared key for each of
the EPs.
During EAP re-authentication, the AAA-Key changes. Whenever the AAA-
Key changes, a new PaC-EP-Master-Key is derived and a new value for
Key-ID is established between the PaC and PAA/EP as defined in [PANA-
PROT]. The [EAP-KEY] document requires that all keys derived from
AAA-key be deleted when the AAA-key expires. Hence, a new IKE PSK
should be derived upon AAA-key expiry. As it also affects the IKE
and IPsec SAs derived from it, new security associations for IKE and
IPsec are established with the new IKE PSK. In case where two runs of
EAP authentication (NAP/ISP) are performed during a single PANA
authentication phase, a new PaC-EP-Master-Key is derived from the
AAA-key obtained from both authentications as specified in the [PANA-
PROT].
6.0 IKE and IPsec details
IKE [RFC2409] MUST be used for establishing the IPsec SA. The details
specified in this document works with IKEv2 [IKEV2] as well as IKE.
Any difference between them would be explicitly noted. PANA
authenticates the client and network, and derives the keys to protect
the traffic. Hence, manual keying cannot be used. If IKE is used,
aggressive mode with pre-shared key MUST be supported. The PaC and EP
SHOULD use the following value in the payload of the ID_KEY_ID to
identify the pre-shared key.
ID_KEY_ID data = (Session-Id | Key-Id)
The Session-Id and Key-Id are the values contained in the data
portion of the Session-Id and Key-Id AVP respectively [PANA-PROT].
They are concatenated to form the content of ID_KEY_ID data. IP
addresses cannot be used as identifier as the same PaC or different
PaC may use the same IP address across a PANA session. For the same
reason, main mode of IKE cannot be used, as it requires addresses to
be used as identifiers.
If IKE is used, a quick mode exchange is performed to establish an
ESP tunnel mode IPsec SA for protecting the traffic between the PaC
and EP. In IKEv2, the initial exchange (IKE_SA_INIT and IKE_AUTH)
creates the IPsec SA also. The identities (a.k.a. traffic selectors
in IKEv2) used during Phase 2 are explained later along with the SPD
entries. As mentioned in section 4.0, an address (POPA) may also have
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to be configured. The address configuration method to be used by the
PaC is indicated in the PANA-Bind-Request message at the end of the
successful PANA authentication. The PaC chooses the appropriate
method and replies back in PANA-Bind-Answer message.
7.0 Packet Formats
Following acronyms are used throughout this document.
PAC-TIA denotes the IPsec-TIA used by the PaC. PAC-TIA may be set to
a PRPA when the same PRPA is used as the IPsec-TIA and IPsec-TOA on
the PaC. Otherwise, PAC-TIA is set to the POPA.
PAC-TOA denotes the IPsec-TOA used by the PaC.
EP-ADDR denotes the address of the EP.
The node with which the PaC is communicating is denoted by END-ADDR.
Following is the IPv4 packet format on the wire for packets sent from
the PaC to the EP:
IPv4 header (source = PAC-TOA,
destination = EP-ADDR)
ESP header
IPv4 header (source = PAC-TIA,
destination = END-ADDR)
Following is the IPv6 packet format on the wire for packets sent from
the PaC to the EP:
IPv6 header (source = PAC-TOA,
destination = EP-ADDR)
ESP header
IPv6 header (source = PAC-TIA,
destination = END-ADDR)
Following is the IPv4 packet format on the wire for packets sent from
the EP to the PaC:
IPv4 header (source = EP-ADDR,
destination = PAC-TOA)
ESP header
IPv4 header (source = END-ADDR,
destination = PAC-TIA)
Following is the IPv6 packet format on the wire for packets sent from
the EP to the PaC:
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IPv6 header (source = EP-ADDR,
destination = PAC-TOA)
ESP header
IPv6 header (source = END-ADDR,
destination = PAC-TIA)
8.0 IPsec SPD entries
The SPD entries for IPv4 and IPv6 are specified separately as they
are different. When the same address is used as IPsec-TIA and IPsec-
TOA, the EP can add the entry to the SPD before the IKE exchange
starts, as it knows the address a priori. When IKEv2 [IKEV2] or
[RFC3456] is used for address configuration, the SPD entry cannot be
created until the IPsec SA is successfully negotiated as the address
is not known a priori. This is very similar to the road warrior case
described in [IPSEC-BIS]. In this case, an SPD entry with a name
selector is used and when the IPsec SA is successfully negotiated, a
new SPD entry is created with the appropriate addresses. The name
would be the contents of ID_KEY_ID payload.
In environments where the PaC is a router, the IPsec-TIA can be a
range of addresses (prefix) instead of a single host address. The PaC
acts like a security gateway in this case establishing the IPsec SA
with another security gateway (EP). This scenario is supported by
[RFC2401] and [IPSEC-BIS]. It is assumed that the PaC obtains the
prefix through other mechanisms not defined in this document. When
the IPsec SA is negotiated, the prefix is carried in the traffic
selectors.
Each SPD entry specifies packet disposition as BYPASS, DISCARD or
PROTECT. The entry that causes the traffic to be protected with IPsec
uses IPsec-TIA as the selector. This has the side effect of
protecting all the traffic, which could be a problem. Some of the
traffic that is not protected with IPsec is discussed below.
. The neighbor discovery messages specified in [RFC2461] are
protected using [RFC3971]. The Multicast listener Discovery
messages specified in [RFC2710] are also bypassed as IKE can
negotiate keys only for unicast traffic. The SPD contains entry
based on ICMPv6 type (130 to 137) to bypass such traffic.
. When IPsec-TIA and IPsec-TOA are the same (as discussed in
section 4.0), the PANA traffic also gets protected with IPsec.
As the IPsec protection adds extra overhead without any benefit,
we need explicit entries to bypass IPsec protection for PANA
traffic on PaC. This may not be needed always for traffic going
from PAA to PaC. If PAA and EP are not co-located, PAA would
send traffic directly to PaC without going through EP. Hence, EP
does not need to have SPD entries to bypass IPsec in this case.
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If PAA and EP are co-located, the PANA packets will be protected
with IPsec only if the IPsec-TIA and IPsec-TOA are same. Hence,
we need explicit entries to bypass IPsec protection when PAA and
EP are co-located. The SPD entry is specified using PANA_PORT.
PANA_PORT is the IANA assigned (TBD) PANA protocol number [PANA-
PROT].
There may be protocols that expect the TTL to be 255, which may not
be preserved as a result of IP forwarding by the EP. If the protocol
termination is in a different place than EP, then we may need
additional bypass entries for those protocols, which are not shown
here. Also, when the PaC is using IPsec for remote access, there may
be additional SPD entries and IPsec security associations, which are
not discussed in this document.
The format chosen to represent the SPD rules is similar to the one
used in [IPSEC-BIS] document (See Appendix E). Following acronyms are
used.
Rule - SPD rule and this column has ordered rules.
LADDR - Local address
RADDR - Remote address
LPORT - Local Port
RPORT - Remote Port
ITYPE - Specifies ICMPv6 type
Action - Specifies the IPsec actions (BYPASS, DROP, PROTECT)
8.1 IPv4 SPD entries
PaC's SPD:
Rule LADDR RADDR LPORT RPORT Action
---- ----- ----- ----- ----- ------
Rule 1 ANY PAA-ADDR ANY PANA_PORT BYPASS
Rule 2 PAC-TIA ANY ANY ANY PROTECT
(ESP, tunnel)
Rule 3 ANY ANY ANY ANY DISCARD
The ESP tunnel's outer source address is PAC-TOA and outer
destination address is EP-ADDR.
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EP's SPD:
Rule LADDR RADDR LPORT RPORT Action
---- ----- ----- ----- ----- ------
Rule 1 PAA-ADDR ANY PANA_PORT ANY BYPASS
Rule 2 ANY PAC-TIA ANY ANY PROTECT
(ESP, tunnel)
Rule 3 ANY ANY ANY ANY DISCARD
The ESP tunnel's outer source address is EP-ADDR and outer
destination address is PAC-TOA.
The phase 2 identities (a.k.a. traffic selectors in IKEv2) differ
depending on how the PaC acquires the PAC-TIA.
. If the client uses PAC-TOA as the PAC-TIA, then it uses PAC-TOA
as the client identity (IDci). The responder identity (IDcr)
would contain the ID_IPV4_ADDR_RANGE with starting address as
zero address (0.0.0.0) and end address as (255.255.255.255).
. If the client uses [RFC3456] for acquiring the PAC-TIA, it needs
to establish the DHCP SA first. This requires additional SPD
entries. Once the PAC-TIA is acquired using DHCP, the DHCP SA is
deleted and a new IPsec tunnel mode SA is established as
specified in this document. When establishing such an SA, PAC-
TIA will be used as the IDci. The responder identity (IDcr)would
contain the ID_IPV4_ADDR_RANGE with starting address as zero
address (0.0.0.0) and end address as (255.255.255.255).
. If IKEv2 is used to obtain the PAC-TIA, the client uses the
configuration request (CFG_REQUEST) along with the traffic
selectors as given in IKEv2. PaC uses IPV4_ADDR_RANGE with
starting address as zero address (0.0.0.0) and end address as
(255.255.255.255) for both TSi and TSr. The EP assigns the
address (PAC-TIA) and returns it in both the configuration
payload (CFG_REPLY) and TSi. The TSr is left to contain the
IPV4_ADDR_RANGE.
8.2 IPv6 SPD entries
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Pac's SPD:
Rule LADDR RADDR LPORT RPORT ITYPE Action
---- ----- ----- ----- ----- ----- ------
Rule 1 ANY ANY ANY ANY 130-137 BYPASS
Rule 2 ANY ANY PANA_PORT ANY ANY BYPASS
Rule 3 PAC-TIA ANY ANY ANY ANY PROTECT
(ESP, tunnel)
Rule 4 ANY ANY ANY ANY ANY DISCARD
The ESP tunnel's outer source address is PAC-TOA and outer
destination address is EP-ADDR.
EP's SPD:
Rule LADDR RADDR LPORT RPORT ITYPE Action
---- ----- ----- ----- ----- ----- ------
Rule 1 ANY ANY ANY ANY 130-137 BYPASS
Rule 2 ANY ANY ANY PANA_PORT ANY BYPASS
Rule 3 ANY PAC-TIA ANY ANY ANY PROTECT
(ESP, tunnel)
Rule 4 ANY ANY ANY ANY ANY DISCARD
The ESP tunnel's outer source address is EP-ADDR and outer
destination address is PAC-TOA.
IKEv2 [IKEV2] is used to configure the PAC-TIA address. The usage of
traffic selectors is very similar to the IPv4 usage as explained in
the previous section. The client may use the interface identifier in
the lower bits of the TSi so that the responder can assign an IPv6
address honoring the interface identifier also.
9.0 Dual Stack Operation
IKEv2 [IKEV2] can enable configuration of IPsec-TIA for both IPv4 and
IPv6 TIAs by sending both IPv4 and IPv6 configuration attributes in
the configuration request (CFG_REQUEST). This enables use of single
IPsec tunnel mode SA for sending both IPv4 and IPv6 traffic.
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Therefore, IKEv2 is recommended for handling dual-stack PaCs where
single execution of IKE is desired.
10.0 IANA Considerations
This document does not make no request to IANA.
10.0 Security considerations
This document discusses the use of IPsec for access control when PANA
is used for authenticating the clients to the access network.
The aggressive mode in IKE [RFC2409] is considered bad due to its DoS
properties i.e., any attacker can bombard IKE aggressive mode packets
making the EP perform heavy diffie-hellman calculations. As the
ID_KEY_ID can be verified by the EP before doing the diffie-hellman
calculation, it prevents random attacks. The attacker now needs to
listen on the traffic between PaC and PAA to originate IKE requests
with valid ID_KEY_ID.
If the EP does not verify whether the PaC is authorized to use an IP
address, it is possible for the PaC to steal the traffic destined to
some other PaC. When IKEv2 [IKEV2] and [RFC3456] are used for address
configuration, the address is assigned by the EP and hence this
attack is not present in such cases. When the same address is used as
both IPsec-TIA and IPsec-TOA, the EP creates the SPD entry with the
appropriate address for the PaC and hence the address is verified
implicitly by the virtue of successful IPsec SA negotiation.
11.0 Normative References
Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9,
RFC 2026, October 1996.
[RFC2401] S. Kent et al., "Security Architecture for the Internet
Protocol", RFC 2401, November 1998
[PANA-PROT] D. Fosberg et al., "Protocol for Carrying Authentication
for Network Access", draft-ietf-pana-06.txt
[RFC4016] M. Parthasarathy, "Protocol for carrying Authentication for
Network Access (PANA) Threat analysis and security requirements",
RFC 4016, March 2005
12.0 Informative References
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[PANAREQ] A. Yegin et al., "Protocol for Carrying Authentication for
Network Access (PANA) Requirements and Terminology", draft-ietf-
pana-requirements-09.txt
[PANA-FRAME] P. Jayaraman et al., "PANA Framework", draft-ietf-pana-
framework-01.txt
[RFC2119] S. Bradner, "Key words for use in RFCS to indicate
requirement levels", RFC 2119, March 1997
[RFC2409] D. Harkins et al., "Internet Key Exchange", RFC 2409,
November 1998
[IKEV2] C. Kauffman et al., "Internet Key Exchange(IKEv2) Protocol",
draft-ietf-ipsec-ikev2-15.txt
[IPSEC-BIS] S. Kent, "Security Architecture for the Internet
Protocol", draft-ietf-ipsec-rfc2401bis-06.txt
[RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
March 1997
[RFC3456] B. Patel et al., "Dynamic Host Configuration Protocol
(DHCPv4) Configuration of IPsec Tunnel Mode", RFC 3456, January
2003
[RFC3315] R. Droms et. al, "Dynamic Host Configuration Protocol for
IPv6", RFC 3315, July 2003
[RFC2461] T. Narten et al., "Neighbor Discovery for IP version 6
(IPv6) ", RFC 2461, December 1998
[RFC2462] S. Thomson et. al, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998
[RFC3041] T. Narten et al., "Privacy Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 3041, January 2001
[EAP-KEY] B. Aboba et al., "EAP Key Management Framework", draft-
ietf-eap-keying-06.txt
[RFC3971] J. Arkko et al., "SEcure Neighbor Discovery (SEND)", RFC
3971, March 2005
[IPV4-LINK] B. Aboba et al., "Dynamic configuration of Link-local
IPv4 addresses", draft-ietf-zeroconf-ipv4-linklocal-12.txt
[RFC1918] Y. Rekhter et al., "Address Allocation for Private
Internets", BCP 5, RFC 1918, February 1996
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[RFC2710] S.Deering et al., "Multicast Listener Discovery (MLD)for
IPv6", RFC 2710, October 1999
[IEEE80211i] IEEE Draft 802.11I/D5.0, "Draft Supplement to STANDARD
FOR Telecommunications and Information Exchange between Systems
LAN/MAN Specific Requirements - Part 11: Wireless Medium Access
Control (MAC) and physical layer specifications: Specification for
Enhanced Security", August 2003.
13.0 Acknowledgments
The author would like to thank Francis Dupont, Pasi Eronen, Yoshihiro
Ohba, Jari Arkko, Hannes Tschofenig, Alper Yegin, Erik Nordmark,
Giaretta Gerardo, Rafa Marin Lopez, Tero Kivinen and other PANA WG
members for their valuable comments and discussions.
14.0 Revision log
Changes between revision 06 and 07
-Changed the format of the SPD to use a table
-Changed the IPv6 SPD entries to use ICMPv6 types
Changes between revision 05 and 06
-Clarified that PRPA can be a global address also in IPv6.
Changes between revision 04 and 05
-working group last call comments (mostly editorial)
Changes between revision 03 and 04
-Comments from Erik Nordmark (mostly editorial)
Changes between revision 02 and 03
-Clarified the use of key-Id in ID_KEY_ID payload
-Clarified the address configuration issues.
-Added an Appendix to clarify implementation issues.
Changes between revision 01 and 02
-Updated the draft with the fixes for all open issues
-Added the IP configuration section
-Modified the IKE pre-shared key derivation to handle PAA controlling
multiple EPs
-Clarification regarding DHCP usage and RFC3456 usage.
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-Only aggressive mode to be supported. Main mode not needed anymore.
Changes between revision 00 and 01
-Specified the use of ESP tunnel mode SA instead of IP-IP transport
mode SA after working group discussion.
-Specified the IKE pre-shared key derivation.
15.0 Appendix A
This section describes the alternate address configuration methods
for Post-PANA address (POPA) and the issues associated with it. As
mentioned in section 4, there are multiple ways by which the PaC may
configure the POPA address. Only [IKEV2] and [RFC3456] address
configuration methods were described in section 4. Other
possibilities and the issues are as follows.
1) Some IKEv1 implementations support IKEv1 MODECFG for configuring
IP address. There is no RFC describing MODECFG feature of IKEv1.
Also, there is not much information on its widespread support
among the implementations. Hence, this document does not
recommend it.
2) The address may also be obtained using DHCP [RFC2131] [RFC3315]
before the IKE exchange starts. Normally the implementations
associate the address and other configuration information (e.g.,
the default router address) with the interface on which the DHCP
is performed. This can cause problems with implementations if
they attempt to use an IP address that is configured via
[RFC2131] [RFC3315] on the physical interface and use it as the
IPsec-TIA on the IPsec tunnel interface. This may work without
problems when the IPsec-TIA and IPsec-TOA are same as the IPv4
PRPA that was obtained using DHCP, as the source address
selection has to deal with just one address. But using an IPv4
IPsec-TOA different than the IPsec-TIA on a single interface may
cause source address selection problem, as there is more than
one address to be dealt with. Similarly, an IPv6 address
obtained and maintained through a physical link but used on a
tunnel interface requires additional implementation
considerations. Therefore, this document does not handle the
case where DHCP is used to acquire an address for the IPsec-TIA
that is different from the IPsec-TOA. Note that this case is
different from the address configuration using [RFC3456], which
also uses DHCP. When [RFC3456] is used, DHCP is run over the
IPsec tunnel and the address (IPsec-TIA) is typically assigned
to the IPsec tunnel interface. The IPsec-TOA is assigned to the
physical interface. As there is only one address on each
interface, there are no address selection issues.
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3) The address may also be obtained using auto-configuration
[RFC2461] including the temporary addresses described in
[RFC3041]. The problem described above for DHCP applies to this
also. The implementations would associate the auto-configured
addresses and the default router with the interface on which the
router advertisement was received. As we configure the SPD to
bypass IPsec for router discovery and neighbor discovery
messages, the address would be associated with the physical
interface and not with the IPsec interface. There is also an
additional issue, as the address configured by the PaC is not
known to the EP. It needs to trust whatever PaC provides in its
traffic selector during the IPsec SA negotiation. This leads to
a DoS attack where the PaC can steal some other PaC's address,
which cannot be prevented unless [RFC3971] is deployed.
16.0 Author's Addresses
Mohan Parthasarathy
313 Fairchild Drive
Mountain View CA-94043
Email: mohanp@sbcglobal.net
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