NEMO Working Group H. Cho
Internet-Draft E. K. Paik
Expires: July 13, 2004 Seoul National University
January 13, 2004
Hierarchical Mobile Router Advertisement for nested mobile networks
<draft-cho-nemo-hmra-00.txt>
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Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes needs for hierarchical mobile router
advertisement for nested mobile networks. When ingress and egress
interfaces of a Mobile Router are both wireless, the MR cannot
distinguish the Router Advertisement of the parent MR from the RA
of the child MR. To maintain hierarchical information of wireless
nested mobile networks, RA message needs to be extended to deliver
additional information for hierarchy.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terms and Abbreviations. . . . . . . . . . . . . . . . . . . 3
3. Router Advertisement (RA) Confliction problem .br
in nested mobile networks. . . . . . . . . . . . . . . . . 3
4. Hierarchical Mobile Router Advertisement (HMRA). . . . . . . 4
4.1. Router Advertisement Message Format. . . . . . . . . . . . 4
4.2. Hierarchy management . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations. . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
References. . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document proposes the Router Advertisement mechanism called
Hierarchical Mobile Router Advertisement (HMRA) for nested mobile
networks. Mobile network is a network that the entire network
moves as a single unit and includes one or more mobile routers
(MRs) that connect it to the global Internet [1]. Mobile routers
use Mobile IPv6 protocol to broadcast Router Advertisement message.
Mobile Network Nodes (MNNs) under an MR can configure their address
and know the connectivity to the MR by listening the RA. Personal
Area Network (PAN) and Vehicle Area Network (VAN) connected to the
Internet are examples of mobile network. Furthermore, PANs in a
vehicle are also possible and this situation is referred to as a
nested mobile network.
Nested mobile networks contain MRs that are not directly attached
to the Internet (i.e. connected to the Internet via another MR). In
the case of nested mobile network, MRs also use Mobile IPv6 RA
mechanism. MRs have ingress and egress interfaces, and each
interface can be wired or wireless. If an MR uses wired ingress
interface, the RA of the MR is delivered to only nodes connected by
wire. But if an MR uses wireless ingress interfaces, all nodes in
its coverage receive the RA of the MR. So when a parent MR has
wireless egress interface and a child MR has wireless egress
interface, the parent MR can listen to the RA of the child MR. This
situation is called "RA Confliction".
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2. Terms and Abbreviations
Age
Age is defined as decreasing value by the distance from AR.
Visiting Mobile Node (VMN)
A mobile node (MN), either a host or a router who can move
topologically with respect to the MR and whose home link
doesn't belong to the mobile network. A VMN that gets
attached to a foreign link within the mobile network
obtains an address on that link. [2]
3. Router Advertisement (RA) Confliction problem
When egress and ingress interfaces of an MR are both wireless,
nested mobile networks have Router Advertisement (RA) confliction
problem. When MRs form nested mobile networks, an MR receives RA
of the child MR as well as the parent MR for the open
characteristics of wireless interface. But the MR cannot
distinguish which MR is its parent. Figure 1 shows the RA
confliction problem. With existing RA scheme [3], MR2 receives both
RAs of MR1 and MR3. So MR2 may think it is under MR3. And in this
situation if MR2 wants to send data to the outside of mobile
network, the packets cannot be routed correctly.
+-----+
| AR | Age = max_age max_age max_age max_age
+-----+
|
+-----+
| MR1 | Age = 0 max_age-1 max_age-1 max_age-1
+-----+
|
+-----+
| MR2 | Age = 0 0 max_age-2 max_age-2
+-----+
|
+-----+
| MR3 | Age = 0 0 0 max_age-3
+-----+
Figure 1. RA Confliction problem
RA confliction problem occurs since MRs and ARs broadcast RA
messages simultaneously. Thus, additional information is needed in
RA message for the management of hierarchy between MRs.
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4. Hierarchical Mobile Router Advertisement (HMRA)
To solve the RA confliction problem of nested mobile networks this
document proposes hierarchical architecture of RA, HMRA. HMRA is
based on the information of hierarchy. For the purpose of
hierarchical management, we employ a field for age in the RA
message. Initially Access Router (AR) has age of maximum value and
MRs have age of zero. The maximum value of age means the maximum
depth of hierarchy.
When an MR receives an RA with an age value, the MR compares
received age with its own age. So if the received age is less than
or equal to its own age, the MR just ignores the RA. And if
received age is bigger than its own age, the MR sets its own age to
smaller age than the received age by one. So each MR can construct
the parent-child relationship by using this age information. When
an MR moved to other network, we can know the movement by the
change of Care-of Address (CoA). So whenever an MR changes its
point of attachment, the MR re-initializes its age to zero and re-
calculates its age again using new RA.
4.1. Router Advertisement Message Format
Figure 2 shows the RA message format with age field.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O| Age |Rsvd | Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 2. Router Advertisement message with "Age" field
ICMP Fields:
Type 134
Code 0
Checksum The ICMP checksum. See [4].
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Cur Hop Limit 8-bit unsigned integer. The default value that
should be placed in the Hop Count field of the IP
header for outgoing IP packets. A value of zero
means unspecified (by this router).
M 1-bit "Managed address configuration" flag. When
set, hosts use the administered (stateful) protocol
for address autoconfiguration in addition to any
addresses autoconfigured using stateless address
autoconfiguration. The use of this flag is
described in [5].
O 1-bit "Other stateful configuration" flag. When
set, hosts use the administered (stateful) protocol
for autoconfiguration of other (non-address)
information. The use of this flag is described in
[5].
Age 3-bit "Age" field for HMRA. Initially Access Router
has age of maximum value and MRs have age of zero.
Rsvd A 3-bit unused field. It MUST be initialized
to zero by the sender and MUST be ignored by the
receiver.
Router Lifetime
16-bit unsigned integer. The lifetime associated
with the default router in units of seconds. The
maximum value corresponds to 18.2 hours. A
Lifetime of 0 indicates that the router is not a
default router and SHOULD NOT appear on the default
router list.
Reachable Time 32-bit unsigned integer. The time, in
milliseconds, that a node assumes a neighbor is
reachable after having received a reachability
confirmation. A value of zero means unspecified
(by this router).
Retrans Timer 32-bit unsigned integer. The time, in
milliseconds, between retransmitted Neighbor
Solicitation messages. A value of zero means
unspecified (by this router).
4.2. Hierarchy management
When an MR moves to the same level of other nested mobile network,
the MR sets its age to zero and listens RA from neighbor MRs. If
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the MR receives RA from the child MR before it receives from the
parent MR, the MR thinks that the child MR is the parent. But after
the MR receives RA of the parent MR, the MR corrects its age. When
an N-level MR moves to an (N-1)-level mobile network, the MR
receives bigger or the same age of RA from neighbor MRs. In this
case re-initializing of age is not necessary. The MR just ignores
the RA of the same age and accepts the RA of bigger age and set its
age to smaller age than received age by one. When an N-level MR
moves to an (N+1)-level mobile network, the MR sets its age to zero
and listens to RA from the neighbor MRs. The next procedures are
the same as the two cases above.
5. Security Considerations
When a malicious MR broadcast RA with the maximum age, hierarchy of
nested mobile network can be confused.
6. Acknowledgements
This work was supported in part by the Brain Korea 21 project of
the Ministry of Education, and in part by the National Research
Laboratory project of the Ministry of Science and Technology,
Korea.
The authors would like to thank people who have given valuable
comments on various nested mobile network issues on the mailing
list.
References
[1] Vijay Devarapalli, Ryuji Wakikawa, Alexandru Petrescu,
and Pascal Thubert, "Nemo Basic Support Protocol",
draft-ietf-nemo-basic-support-01.txt, September 2003,
work in progress.
[2] Thierry Ernst, and Hong-Yon Lach,
"Network Mobility Support Terminology",
draft-ietf-nemo-terminology-00.txt, May 2003,
work in progress.
[3] T. Narten, E. Nordmark, and W. Simpson,
"Neighbor Discovery for IP Version 6", RFC2461,
December 1998.
[4] Conta, A. and S. Deering,
"Internet Control Message Protocol (ICMPv6)
for the Internet Protocol Version 6 (IPv6) Specification",
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RFC 2463, December 1998.
[5] Thomson, S. and T. Narten, "IPv6 Address Autoconfiguration",
RFC 2462, December 1998.
Authors' Addresses
Hosik Cho
Multimedia and Computer Communications Lab.
Seoul National University
ENG4190, School of Electronic Engineering and Computer Science
Seoul National University
Seoul 151-744, Korea
Phone: +82 2 880 1832
Fax: +82 2 872 2045
EMail: hscho@mmlab.snu.ac.kr
Eun Kyoung Paik
Multimedia and Computer Communications Lab.
Seoul National University
ENG4190, School of Electronic Engineering and Computer Science
Seoul National University
Seoul 151-744, Korea
Phone: +82 2 880 1832
Fax: +82 2 872 2045
EMail: eun@mmlab.snu.ac.kr
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