autoconf Working Group Jaehwoon Lee
Internet Draft Dongguk University
Expires: April 29, 2009 Sanghynn Ahn
University of Seoul
Younghan Kim
Soongsil University
Yuseon Kim
Sangeon Kim
KT
October 30, 2008
Address Autoconfiguration for the subordinate MANET with Multiple MBRs
draft-jaehwoon-autoconf-mmbr-01.txt
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Internet-Draft Address Autoconfiguration for multiple MBRs Oct. 30, 2008
Abstract
In order to allow the subordinate MANET to be connected to the
external network, the MANET border router (MBR) has been defined. For
providing scalability and reliability to the subordinate MANET,
multiple MBRs may be deployed. One of the issues on the subordinate
MANET with multiple MBRs is which network prefixes are to be
advertised by MBRs. In the case when MBRs advertise different network
prefixes, if a MANET node changes its default MBR to a new one, the
node may have to transmit packets via non-optimal paths to keep using
the existing connection to the previous MBR, or change its address by
using the network prefix information from the new MBR. In the latter
case, on-going sessions can be terminated because of the address
change. In this draft, we define a PMIPv6 based address
autoconfiguration mechanism that enables MANET nodes to operate
properly when all MBRs advertise the same network prefix in the
subordinate MANET.
Table of Contents
1. Introduction..................................................3
2. Terminology...................................................4
3. Message format................................................4
3.1 Registration Request message..............................4
3.2 Registration Confirmation message.........................4
4. Protocol operation............................................4
5. Security Considerations.......................................7
6. IANA Considerations...........................................7
References.......................................................7
Author's Addresses...............................................8
Intellectual Property and Copyright Statements ..................9
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1. Introduction
The mobile ad hoc network (MANET) enables mobile nodes to communicate
via multiple wireless hops without the need of any wired
infrastructure. In a MANET, two nodes not within their transmission
range have to deliver data to each other through other intermediate
nodes. For forwarding packets destined to other nodes, each node must
have the routing capability, i.e., the mechanism for establishing
data delivery routes between any pair of source and destination
nodes. The IETF MANET working group has defined route setup
mechanisms for delivering data between MANET nodes. Especially for an
ad hoc network such as the MANET, the mechanism that can allow
nodes to configure their addresses autonomically is more desirable
than the static address configuration mechanism since the former has
less configuration and management overhead by not incurring manual
intervention.
The MANET can be classified into the subordinate MANET or the
autonomous MANET depending on whether it is connected to the external
network or not[1]. The MANET border router (MBR) which is a gateway
device connecting the MANET with the external network has been
defined for the subordinate MANET. As the number of nodes in the MANET
increases, the amount of traffic between the MANET and the Internet
increases, so the MBR gets overloaded, resulting in the overall
network performance degradation. To overcome this problem, multiple
MBRs can be used for the Internet connectivity [2]. Mechanisms in
which each MBR advertises a different network prefix have been
proposed for the MANET with multiple MBRs[3-4]. However, in these
mechanisms, if a node moves to another place, it sends packets via
non-optimal paths to maintain its connection to the previous MBR, or
it changes its address by using the network prefix from the new MBR.
In the latter case, an on-going session may get terminated because
of the address change.
In this draft, we define an address autoconfiguration mechanism for
the subordinate MANET with multiple MBRs which advertise the same
network prefix. In the proposed mechanism, since all MBRs advertise
the same network prefix, even a node moves it can still use its
preconfigured address. That means that no address reconfiguration
is needed in case of node movement, so the proposed mechanism has
the advantage of keeping on maintaining its existing session(s).
Furthermore, under node movement, a node can still find an optimized
path without changing its address because it can choose the MBR
that can be reached via the minimum number of hops.
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2. Terminology
TBD.
3. Message Format
3.1 Registration Request (RR) Message
TBD
3.2 Registration Confirmation (RC) Message
TBD
4. Protocol Operation
MR MBR1(MAG1) MBR2(MAG2) LMA (internet) CN
| | | | |
|<----------| | | |
ICMP SERA message | | |
(Configure IPv6 address to MANET interface) | |
|<--------->| | | |
(DHCP with prefix delegation) | | |
|---------->| | | |
|RR message | | | |
| |---------------------------------->| |
| | PBU message (Create Binding Cache Entry) |
| |<----------------------------------| |
| | PBAck message | |
|<----------| | | |
|RC message | | | |
|<--------->|<=================================>|<------------>|
| Data packet transfer between MR and CN via MBR1 and LMA |
(MR changes its default gateway from MBR1 to MBR2) | |
|<---------------------------| | |
| ICMP SERA message | | |
|--------------------------->| | |
| RR message | | |
| | |----------------->| |
| | | PBU message | |
| | | (Update Binding Cache Entry |
| | |<-----------------| |
| | | PBAck message | |
|<---------------------------| | |
| RC message | | |
|<-------------------------->|<================>|<------------>|
| Data packet transfer between MR and CN via MBR2 and LMA |
| | | | |
Figure 1: Message exchange scenario
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The message exchange scenario considered in this draft is depicted
in figure 1. The network is composed of the external network such as
the global Internet, a PMIPv6 domain and a MANET. The operation of
the PMIPv6 protocol is defined in [5]. In the PMIPv6 domain, a local
mobility anchor (LMA) is located and acts as a kind of home agent
(HA). The MANET can be connected to the PMIPv6 domain through a
multiple number of mobility access gateways (MBRs) and an MBR
operates as a mobility access gateway (MAG) in the PMIPv6 domain.
One network prefix is assigned to the MANET, and each MBR
periodically advertises scope-extended Router Advertisement
(SERA) messages to the entire MANET [6]. The SERA message is defined
to resolve the duplicate packet reception problem which can occur in
a multi-hop wireless network such as the MANET. The network prefix
assigned to the MANET and the address of the MBR originating the
SERA message are included in the message. Even though the MBR
address information included in the SERA messages sent by different
MBRs, the network prefixes MBR addresses that can be derived by
using the prefix length are the same. In other words, the MBRs
connecting the MANET and the global Internet advertise the same
network prefix.
A MANET node is composed of a MANET router (MR) and hosts [7].
A MR has a MANET interface to connect to the MANET and IP interfaces
to connect to hosts. When a MR connects to the MANET for the first
time, it waits for a SERA message from a MBR. Assume that the SERA
message from MBR1 arrives first. Then the MR configures the IPv6
address of its MANET interface by utilizing the stateless address
autoconfiguration mechanism based on its MAC address and the network
prefix obtained from the MBR1 address and the network prefix
length [8]. After that, the MR sets the MBR1 address in the SERA
message as the address of its default gateway, and stores the
distance to MBR1 which can be calculated with
'255 - the Cur Hop Limit in the scope-extended RA message + 1'
in its routing table. In addition to that, the MR sets the value in
the source IP address field of the IP packet having the received
SERA message as the next-hop address to its default gateway and
records this information in its routing table. Then, the MR decreases
the Cur Hop Limit value in the received SERA message by 1 and
broadcasts the modified SERA message. Also, the MR sends a
Registration Request (RR) message to MBR1. Upon receiving the RR
message, MBR1 sends a Proxy Binding Update (PBU) message with the
MR address to the LMA. The LMA stores the binding information for
the MR and MBR1 and sends a Proxy Binding Acknowledgement (PBAck)
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message to MBR1. After that, a tunnel between the LMA and MBR1 is
established for the MR. After receiving the PBAck message from the
LMA, MBR1 sends a Registration Confirmation (RC) message to the MR.
Now, the MR can communicate with any host in the global Internet.
That is, if MBR1 receives a packet from the MR, it transmits the
packet to the LMA via the established tunnel which, in turn, forwards
it to the destination host in the global Internet.
Since SERA messages are periodically advertised by each MBR, a MR can
receive SERA messages advertised by another MBR even after it has
configured an IPv6 address of its MANET interface. The operation of a
MR receiving a SERA message is as follows. Once a MR receives a
SERA message broadcasted by the neighbor node which is set as the
next-hop node to its default gateway, the MR updates its
corresponding routing table entry using the information in the
received SERA message. That is, the MR determines the distance to its
default gateway based on the Cur Hop Limit value in the SERA message.
Moreover, if the MBR address in the SERA message is different from
its current default gateway, the MR changes its default gateway to
the MBR (i.e., MBR2) specified in the SERA message and sends a RR
message to MBR2. After that, the MR broadcasts the SERA message
with the modified Cur Hop Limit value. If the MR receives a
SERA message from another neighbor node which is not the next-hop
node to the default gateway, the MR compares the distance to the MBR
having sent the SERA message (which can be computed from the Cur Hop
Limit value in the SERA message) and that to its default gateway.
If the former one is larger than or equal to the latter,
it discards the received SERA message. Otherwise, it updates its
corresponding routing table entry based on the information in the
received SERA message. That is, the MR changes the distance to the
default gateway to the distance value obtained from the SERA message
and sets the neighbor node as the next-hop node to the default
gateway. And, if the MBR address in the SERA message is different
from the address of its default gateway, the MR changes its default
gateway to the MBR specified in the SERA message and sends an RR
message to the new default gateway. After that, the MR broadcasts
a SERA message with the modified distance value. In this case,
even when the default gateway is changed, the network prefix for the
MANET is kept the same, so the MR can keep on maintaining its
on-going session(s) because it can still use its IPv6 address
configured on its MANET interface. Furthermore, even if the MR
changes its default gateway, the IPv6 address configured on its
MANET interface is kept the same. Thus, if the packets from a host
in the Internet arrive at the MBR chosen as its previous default
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gateway before the registration process is completed, they can be
delivered to the MR via the previous default gateway, so no packet
loss due to address changes will happen.
If the MR does not receive a SERA message from its next-hop node to
the default gateway for some time duration or it determines that the
next-hop node is no more its neighbor node, the MR deletes the
default gateway related entry from its routing table.
5. Security Consideration
TBD.
6. IANA Considerations
TBD.
References
[1] E. Baccelli et al., "Address Autoconfiguration for MANET:
Terminology and Problem Statement", draft-ietf-autoconf-
statement-04, Work in progress, Feb. 2008.
[2] S. Ruffino, P. Stupar and T. Clausen, "Autoconfiguration in a
MANET: connectivity scenarios and technical issues", draft-
ruffino-manet-autoconf-scenarios-00, work in progress, Oct. 2004.
[3] S. Ruffino and P. Stupar, "Automatic configuration of IPv6
addresses for MANET with multiple gateways (AMG)",
draft-ruffino-manet-autoconf-multigw-03, work in progress,
June 2006.
[4] C. Jelger, T. Noel and A. Frey, "Gateway and address
autoconfiguration for IPv6 adhoc networks", draft-jelger-manet-
gateway-autoconf-v6-02, work in progress, apr. 2004.
[5] S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury and
B. Patil, "Proxy Mobile IPv6", RFC 5213, Aug. 2008.
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[6] J. H. Lee, S. Ahn, Y. Kim, Y. Kim and S. Kim, "Scope-Extended
Router Advertisement for Connected MANETs", draft-jaehwoon-
autoconf-sera-00, Work in progress, July 2008.
[7] I. Chakeres, J. Macker and T. Clausen, "Mobile Ad hoc Network
Architecture", draft-ietf-autoconf-manetarch-07,
Work in progress, Nov. 2007.
[8] S. Thomson and T. Narten, "IPv6 Stateless Address A
utoconfiguration", RFC 2462, Dec. 1998.
Author's Addresses
Jaehwoon Lee
Dongguk University
26, 3-ga Pil-dong, Chung-gu
Seoul 100-715, KOREA
Email: jaehwoon@dongguk.edu
Sanghyun Ahn
University of Seoul
90, Cheonnong-dong, Tongdaemun-gu
Seoul 130-743, KOREA
Email: ahn@uos.ac.kr
Younghan Kim
Soongsil University
11F Hyungnam Engineering Bldg. 317, Sangdo-Dong,
Dongjak-Gu, Seoul 156-743 Korea
E-main: yhkim@dcn.ssu.ac.kr
Yuseon Kim
KT
17 Woomyeon-dong, Seocho-gu
Seoul 137-792, KOREA
Email: yseonkim@kt.co.kr
Sangeon Kim
KT
17 Woomyeon-dong, Seocho-gu
Seoul 137-792, KOREA
Email: sekim@kt.co.kr
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