NEMO Working Group Vijay Devarapalli
INTERNET DRAFT Nokia
21 June 2003 Ryuji Wakikawa
Category: Standards Track Keio University
Alexandru Petrescu
Motorola
Pascal Thubert
Cisco Systems
Nemo Basic Support Protocol
draft-ietf-nemo-basic-support-00.txt
Status of This Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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other groups may also distribute working documents as Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at:
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at:
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Abstract
This document describes a protocol to support network mobility as the
mobile network attaches to different points in the Internet. The
protocol allows for session continuity for every node in the mobile
network as the network moves. It also allows every node in the
mobile network to be reachable while moving around. The protocol is
based on extensions to Mobile IPv6 [1]. The Mobile Router [2] which
connects the network to the Internet runs the NEMO protocol with its
Home Agent. The protocol is designed in such a way that network
mobility is transparent to the nodes inside the mobile network.
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Contents
Status of This Memo 1
Abstract 1
1. Introduction 4
2. Terminology 5
3. Overview of the NEMO Protocol 7
4. Message Formats 10
4.1. Binding Update . . . . . . . . . . . . . . . . . . . . . 10
4.2. Binding Acknowledgement . . . . . . . . . . . . . . . . . 10
4.3. Mobile Network Prefix Option . . . . . . . . . . . . . . 11
4.4. Mobile Network Prefix Length Option . . . . . . . . . . . 12
5. Mobile Router Operation 14
5.1. Data Structures . . . . . . . . . . . . . . . . . . . . . 14
5.2. Sending Binding Updates . . . . . . . . . . . . . . . . . 15
5.3. Receiving Binding Acknowledgements . . . . . . . . . . . 15
5.4. Error Processing . . . . . . . . . . . . . . . . . . . . 16
5.5. Establishment of Bi-directional Tunnel . . . . . . . . . 17
5.6. Neighbour Discovery for Mobile Router . . . . . . . . . . 18
5.7. Multicast Groups for Mobile Router . . . . . . . . . . . 18
6. Home Agent Operation 19
6.1. Prefix Table . . . . . . . . . . . . . . . . . . . . . . 19
6.2. Mobile Network Prefix Registration . . . . . . . . . . . 19
6.3. Advertising Mobile Network Reachability . . . . . . . . . 21
6.4. Establishment of Bi-directional Tunnel . . . . . . . . . 21
6.5. Forwarding Packets . . . . . . . . . . . . . . . . . . . 21
6.6. Sending Binding Acknowledgements . . . . . . . . . . . . 22
6.7. Mobile Network Prefix De-Registration . . . . . . . . . . 23
7. Extended Home Network 24
8. Support for Dynamic Routing Protocols 26
9. Use of IPsec to protect the Signaling Messages 27
10. Security Considerations 28
11. IANA Considerations 28
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12. Contributors 28
13. Acknowledgements 28
A. Examples of Operation 31
Addresses 34
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1. Introduction
This document describes protocol extensions to Mobile IPv6 (MIPv6)
[1] to enable support for network mobility. The extensions provide
a backward compatibility with Mobile IPv6, and in particular, a Nemo
compliant Home Agent can operate as a MIPv6 Home Agent as well.
The Nemo Basic Support works in such a way that session continuity is
ensured for all the nodes in the mobile network even as the Mobile
Router changes its point of attachment to the Internet. It also
provides connectivity and reachability for all nodes in the mobile
network as the network moves. The solution supports both Local Fixed
Nodes [2] and Mobile Nodes in the Mobile Metwork.
Within the context of this document, the definition of a Mobile
Router extends that of a Mobile IPv6 [1] Mobile Node, by adding
the capability of routing between its point of attachment (Care-of
Address) and a subnet which moves with the Mobile Router.
The solution described in this document requires setting up a
bi-directional tunnel between the Mobile Router and its Home Agent.
This tunnel is set up when the Mobile Router sends a successful
Binding Update to its Home Agent, informing the Home Agent of its
current point of attachment.
All traffic between the nodes in the Mobile Network and Correspondent
Nodes passes through the Home Agent. This document does not describe
how to route optimize this traffic. Route Optimization will be dealt
with in later specifications.
IPsec is used to secure all signalling messages between the Mobile
Router and its Home Agent. The use of IPsec to protect the signaling
messages is described in [3]. This document does not introduce any
additional requirements as far as the use of IPsec is concerned.
The terminology document [2] describes Nested Mobility as a scenario
where a Mobile Router allows another Mobile Router to attach to its
mobile network. There could be arbitrary levels of nested mobility.
The operation of each Mobile Router remains the same whether the
Mobile Router attaches to another Mobile Router or to a fixed Access
Router on the Internet. The solution described here does not place
any restriction on the number of levels for nested mobility. But
it should be noted that this might introduce important overhead on
the data packets as each level of nestedness introduces another IPv6
header encapsulation.
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2. Terminology
There is a separate NEMO terminology document [2], which defines the
terms related to Network Mobility used in the document.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2].
Prefix Table
It is a list of a mobile network prefixes indexed
by the extended Home Address of a Mobile Router. The
prefix table is managed by the Home Agent. When a Home
Agent receives a Binding Update without any options,
it searches a correspondent Mobile Network prefix in
the prefix table, keying with the Home Address of the
requesting Mobile Router. This is an optional data
structure.
Mobile Network Prefix
The IPv6 prefix advertised in the Mobile Network
by one or more Mobile Routers. There could be multiple
prefixes in the Mobile Network.
extended Home Network Prefix
The aggregation of one or more Home Network and
Mobile Network prefixes. The extended Home Network
is generally the granularity that is exposed by the
Home Agents to the routing infrastructure over routing
protocols.
extended Home Network
The network associated with the extended Home
Network Prefix. The extended Home Network may be physical
or virtual.
extended Home Address
The Home Address is derived from the Home Network
prefix. The extended Home Address is taken from the
extended Home Network. More precisely, the extended Home
Address can be either from the Home Network or from one of
the Mobile Router's Mobile Network prefixes. The extended
Home Address inherits from the properties of the Home
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Address and can be used for registration to the Home Agent
as described in this document.
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3. Overview of the NEMO Protocol
A Mobile Network is a network segment or subnet which can move
and attach to arbitrary points in the Internet. A Mobile Network
does not allow any transit traffic and can only be accessed via
specific Gateways called Mobile Routers that manage its movement.
A Mobile Router does not distribute the Mobile Network routes to
the infrastructure at its point of attachment (i.e. in the visited
network). Instead, it maintains a bidirectional tunnel to a Home
Agent that advertises an aggregation of Mobile Networks to the
infrasructure. The Mobile Router is also the default gateway for the
Mobile Network.
A Mobile Network can also consist of multiple and nested subnets. In
particular, a router with no support for mobility may be permanently
attached to a Mobile Network for local distribution. Also, Mobile
Routers may be attached to Mobile Networks owned by different Mobile
Routers and form a graph. In particular, with Basic Nemo Support,
each Mobile Router is attached to another Mobile Network by a single
interface, and if loops are avoided, the graph is a tree.
A Mobile Router has an unique Home Address through which it is always
reachable. The Home Address is configured from a prefix that is
aggregated and advertised by its Home Agent. The prefix could either
be the prefix advertised on the home link or the prefix delegated
to the Mobile Router. This is described in detail in Section 7.
The Mobile Router can have more than one Home Address if there
are multiple prefixes in the home link. The Mobile Router also
advertises one or more prefixes in the mobile network attached to it.
The actual mechanism for allocating these Mobile Network Prefixes is
outside the scope of this specification. However, it is recommended
that these prefixes are allocated in such a manner that they can be
aggregated under the home link.
When the Mobile Router moves away from the home link and attaches
to a new access router, it acquires a Care-of Address from the
visited link. The Mobile Router at any time can appear and behave
as a Mobile Host or a Mobile Router. If the Mobile Router wants
connectivity, rechability and session continuity for nodes in the
Mobile Network, it acts as a Mobile Router. In either case, as soon
as the Mobile Router acquires a Care-of Address, it immediately sends
a Binding Update to its Home Agent as described in [1]. When the
Home Agent receives this Binding Update it creates a binding cache
entry binding the Mobile Router's Home Address to its Care-of address
at the current point of attachment.
If the Mobile Router wishes to act as a Mobile Router and provide
connectivity to nodes in the Mobile Network, it indicates this to
the Home Agent by setting a flag 'R' in the Binding Update. It also
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includes information about the Mobile Network Prefix in the Binding
Update using one of the modes described in Section 5.2, so that
the Home Agent can forward packets meant for nodes in the mobile
network to the Mobile Router. Two new Mobility Header Options are
described in this document to carry prefix information. These new
options are described in Section 4.3 and section 4.4. If the Mobile
Network has more than one IPv6 prefix and wants the Home Agent to
setup forwarding for all these prefixes, it includes multiple prefix
information options in a single Binding Update. The Home Agent sets
up forwarding for each of these prefixes to the Mobile Router's
Care-of Address. In some scenarios the Home Agent already knows
which prefixes are owned by a Mobile Router. In these scenarios, the
Mobile Router does not include any prefix information in the Binding
Update. The Home Agent sets up forwarding for all prefixes owned by
the Mobile Router, when it receives a Binding Update from the mobile
router.
If the Home Agent successfully processes the Binding Update and
sets up forwarding for the Mobile Network Prefix, it sends a
Binding Acknowledgement to the Mobile Router. Once the binding
process completes, a bi-directional tunnel is established between
the Home Agent and the Mobile Router. The tunnel end points are
Mobile Router's Care-of Address and the Home Agent's address. If
a packet with a source address belonging to the Mobile Network
Prefix is received from the Mobile Network, the Mobile Router
reverse-tunnels the packet to the Home Agent through this tunnel.
This reverse-tunneling is done by using IP-in-IP encapsulation [4].
The Home Agent decapsulates this packet and forwards it to the CN.
The Mobile Router is however free to use route optimization as
described in [1] for packet originated by the Mobile Router itself.
When a data packet is sent by a Correspondent Node to a node in the
Mobile Network, it gets routed to the Home Agent which currently
has the binding for the Mobile Router. It is expected that the
Mobile Router's network prefix would be aggregated at the Home
Agent, which advertises the resulting aggregation. Alternatively,
the Home Agent may receive the data packets meant for the Mobile
Network by advertising routes to the Mobile Network prefix. The
actual mechanism by which these routes are advertised is outside
the scope of this document for now. When the Home Agent receives a
data packet meant for a node in the mobile network, it tunnels the
packet to Mobile Router's current Care-of address. The Mobile Router
decapsulates the packet and forwards it onto the link where the
Mobile Network is connected.
The Mobile Network could consist of nodes which are Local Fixed
Nodes, Local Mobile Nodes and Visiting Mobile Nodes [2]. The
protocol described here ensures complete transparency of network
mobility to the Local Fixed Nodes. Visiting Mobile Nodes are those
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nodes which are Mobile Nodes as described in Mobile IPv6. Visiting
Mobile Nodes treat the Mobile Network as just a normal IPv6 access
network and run the Mobile IPv6 protocol.
It is also possible for the Mobile Router and the Home Agent to
run a routing protocol through the bi-directional tunnel. The
Mobile Router need not include prefix information in the Binding
Update. Instead the Home Agent uses the routing protocol updates to
setup forwarding for the Mobile Network. When running the routing
protocol it is required that the bi-directional tunnel be treated as
a tunnel interface. The tunnel interface is included as the list of
interfaces on which routing protocol is active. The Mobile Router
should be careful to not run the routing protocol on its egress
interface when it is away from the home link.
Finally, the Home Agent(s) may be configured with static routes to
the Mobile Network Prefix via the Mobile Router home address.. In
that case, the routes are set independently of the binding flows and
the returning Home of a Mobile Router. The benefit is that such
movement does not induce any additional signalling in the form of
routing updates in the Home Network. The drawback of that model is
that the routes are present even if the Mobile Routers that are not
reachable (at Home or bound) at a given point of time.
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4. Message Formats
4.1. Binding Update
A new flag `R' is included in the Binding Update to indicate to the
Home Agent if the Binding Update is coming from a Mobile Router
and not from a mobile node. The rest of the Binding Update format
remains the same as defined in [1].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K|R| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Mobile Router Flag(R)
The Mobile Router Flag is set to indicate to the Home Agent
that the Binding Update is from a Mobile Router. If the flag
is set to 0, the Home Agent assumes that the Mobile Router is
just behaving as a Mobile Node, and should not forward packets
destined for the mobile network to the Mobile Router.
Mobility Options
Variable length field which can include zero or more mobility
options. This document defines two new mobility options in
addition to what is defined [1]. The receiver MUST skip and
ignore any options which it does not understand.
4.2. Binding Acknowledgement
There is no change in the Binding Acknowledgement format from what
is used in Mobile IPv6 [1]. However, this document introduces the
following new status values for the binding acknowledgement.
Status
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140 Mobile Router Operation not permitted
141 Invalid Prefix
142 Not Authorized for Prefix
143 Mobile Network Prefix information unavailable.
Status values less than 128 indicate that the Binding Update was
processed successfully by the receiving nodes. Values greater than
128 indicate that the Binding Update was rejected by the receiving
node.
4.3. Mobile Network Prefix Option
The Mobile Network Prefix Option is included in the Binding Update
to indicate to the Home Agent the prefix information for the mobile
network. There could be multiple Mobile Network Prefix Options
if the Mobile Router has more than one IPv6 prefix in the Mobile
Network and wants the Home Agent to forward packets for each of these
prefixes to the Mobile Router's current location.
The Mobile Network Prefix Option has an alignment requirement of
8n+4. Its format is as follows.
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 | Length | Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Mobile Network Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
TBD
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Length
8 bit unsigned integer indicating the length in octets of the
option excluding the type and length fields. Set to 18.
Reserved
Set to 0. Ignored for now.
Prefix Length
8 bit unsigned integer indicating the length of the IPv6 prefix
contained in the option.
Mobile Network Prefix
A 16 byte field contains the Mobile Network Prefix.
4.4. Mobile Network Prefix Length Option
The Mobile Network Prefix Length Option can be used by the Mobile
Router if the Mobile Network Prefix can be deduced from the Home
Address of the Mobile Router. If there is only one Mobile Network
Prefix owned by the Mobile Router, using this option helps in
saving 16 bytes in the Binding Update by not including the prefix
information.
There can only be one instance of this option in a Binding Update.
The Mobile Network Prefix Option cannot be present in the Binding
Update if this option is present.
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 | Length | Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
TBD
Length
8 bit unsigned integer indicating the length in octets of the
option excluding the type and length field. Set to 2.
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Reserved
Set to 0. Ignored for now.
Prefix Length
8 bit unsigned integer indicating the length of the IPv6 prefix
contained in the option
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5. Mobile Router Operation
Mobile Router operation is derived largely from the combined
behaviors of a Host, of a Router [8], and of a Mobile Node [1] (also
please see definition of a Mobile Host in [2] and the definition of
an IPv4 Mobile Node [10]).
A Mobile Node can act in two different ways: (1) as a Mobile Host
(in which case the Mobile IPv6 Home Agent doesn't maintain any prefix
information related to the Mobile Host's Home Address, but does
maintain a binding cache entry related to the Mobile Host's Home
Address) and (2) as a Mobile Router (in which case, in addition to
maintaining the binding cache entry corresponding to the Mobile
Router Home Address, the Mobile IPv6 Home Agent also maintains
forwarding information related to prefixes assigned to the Mobile
Network). The distinction between the the two modes is represented
by the value of the 'R' bit.
Mobile Router uses various data structures, exchanges specific
binding messages with Home Agent, performs a specific Neighbour
Discovery behavior and joins certain multicast groups.
5.1. Data Structures
Like a Mobile Host, a Mobile Router also maintains a Binding Update
List, described in section 11.1 of Mobile IPv6 specification[1]. The
Binding Update list is a conceptual data structure which records
information that is sent in the Binding Updates. There is one entry
per each destination that the Mobile Router is currently sending
Binding Updates to.
This document introduces a new Prefix Information field in the
Binding Update list structure. This field is used to store any
prefix information that the Mobile Router includes in the Binding
Update. If the Mobile Router sets the 'R' bit in the Binding Update,
but does not include any prefix information in it (implicit mode),
this field is set to null.
Similar to a Mobile Host, a Mobile Router also stores the information
regarding status of flags of the Binding Update, in the corresponding
Binding Update List entry. Additionally, this document introduces a
new mobile router flag 'R' for this entry. The status of this flag
is stored in the Binding Update list whenever a Binding Update is
sent.
Similarly to a Mobile Host, a Mobile Router maintains a Home Agent
list populated according to the same procedure as a Mobile Host.
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5.2. Sending Binding Updates
A Mobile Router will send Binding Updates to its Home Agent according
to the same procedures that a Mobile Host uses. The Mobile Router
MUST use one of the following modes to instruct the Home Agent to
determine the Mobile Network prefix. In all three modes, the Mobile
Router sets the 'R' bit to 1.
Implicit:
In this mode, the Mobile Router does not include either a
Mobile Network Prefix Option or a Mobile Network Prefix Length
Option in the Binding Update (but it does include the Home
Address Option in the Destination Options header, as all Mobile
Hosts do). The Home Agent can use any mechanism (not defined
in this document) to determine the Mobile Network Prefix(es)
owned the Mobile Router. One of the well known mechanisms is
where the Home Agent maintains a Pre-configured Prefix Table
listing all the Mobile Network prefixes owned by a particular
Mobile Router. This table is keyed on the Home Address of the
Mobile Router.
Explicit:
In this mode, the Mobile Router includes one or more Mobile
Network Prefix Options in the Binding Update. These options
contain information about the Mobile Network Prefix(es)
configured on the Mobile Network.
Explicit combined:
In this mode, the Mobile Router instructs the Home Agent to
derive the Mobile Network Prefix by using: (1) the Home
Address in the Home Address Option carried in the Destination
Options header of the same packet that carries the Mobility
Header containing this Binding Update and (2) the prefix length
carried in the Mobile Network Prefix Length Option. In this
case, Mobile Router includes one and only one Mobile Network
Prefix Length Option. It MUST not include a Mobile Network
Prefix Option if this method is used.
If the Mobile Router flag is set, The Mobile Router MUST also set the
Home Registration flag 'H'.
5.3. Receiving Binding Acknowledgements
The Mobile Router receives Binding Acknowledgements from the Home
Agent, corresponding to the Binding Updates it sent. If the Binding
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Acknowledgement status is set to a value less than 128, the Mobile
Router assumes that the Binding Update was processed succesfully
by the Home Agent. The Mobile Router can then start using the
bi-directional tunnel for reverse tunneling traffic from the mobile
network.
5.4. Error Processing
If the Binding Acknowledgement status is set to a value between 128
and 140, the Mobile Router takes necessary actions as described in
the Mobile IPv6 specification [1].
If the Mobile Router sent a Binding Update to the Home Agent in
implicit mode (i.e. the prefix field in the Binding Update list
entry is null) then the Mobile Router interprets only the error
status '140' (Mobile Router Operation not permitted) and '143'
(Mobile Network Prefix information unavailable). For this Binding
Update, the Mobile Router will discard Binding Acknowledgements with
codes '141' and '142', and log the information.
For the same Binding Update, if the status is '140', Mobile Router
SHOULD send a similar Binding Update (implicit mode) to another Home
Agent on the same home link. If no Home Agent replies positively
then the Mobile Router MUST refrain from sending any Binding Update
with the 'R' bit set to any Home Agent on the home link, and log the
information.
For the same Binding Update, if the status is '143', Mobile Router
SHOULD send a similar Binding Update (implicit mode) to another Home
Agent on the same home link. If no Home Agent replies positively
then Mobile Router SHOULD refrain from sending this Binding Update
to any Home Agent on the home link, and MAY send Binding Updates in
another mode (e.g. explicitly include a prefix) to a Home Agent on
the same home link.
If the Mobile Router sent a Binding Update to Home Agent in any other
mode than implicit mode (i.e. the prefix field in the Binding Update
list entry is not null) then the Mobile Router interprets only the
error status '141' (Invalid Prefix) and '142' (Not Authorized for
Prefix). For this Binding Update, the Mobile Router will discard
Binding Acknowledgements with codes '140' and '143', and log the
information.
For the same Binding Update, if the status is set to '141', then the
Mobile Router should send a similar Binding Update (same explicit
prefix(es) or prefix lens) to another Home Agent on the same home
link. If no Home Agent replies positively then Mobile Router SHOULD
refrain from sending this Binding Updates to any Home Agent on the
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home link. At this point, Mobile Router MAY try try to obtain and
own a prefix by the same means that it initially got attributed the
Invalid Prefix in question. Alternatively, Mobile Router MAY send
Binding Updates in another mode (e.g. implicit mode) to a Home Agent
on the same home link.
For the same Binding Update, if the status is set to '142', then the
Mobile Router should send a similar Binding Update (same explicit
prefix(es) or prefix lens) to another Home Agent on the same home
link. If no Home Agent replies positively then Mobile Router SHOULD
refrain from sending this Binding Updates to any Home Agent on the
home link. Additionally, the Home Agent MUST stop advertising
the respective prefix(es) in the mobile network with associated
Router Advertisements, and modify its own forwarding information
accordingly. Following this, the Mobile Router MAY send Binding
Updates in another mode (e.g. implicit) to a Home Agent on the same
home link.
If at the end of this Error Processing procedure the Mobile Router
has tried every available modes of sending Binding Updates and still
has not received a positive Binding Acknowledgement (status valued 0)
for this Home Address from any Home Agent on its home link, then the
Mobile Router MUST stop sending Binding Updates with the 'R' bit set
for this Home Address and log the information.
In all the above cases, the Mobile Router should assume that the Home
Agent did not create a binding cache entry for the Mobile Router's
home address.
5.5. Establishment of Bi-directional Tunnel
Only when a successful Binding Acknowledgement ('Status' field valued
0) is received will the Mobile Router set up its endpoint of the
bi-directional tunnel.
The bi-directional tunnel between Mobile Router and Home Agent allows
packets to flow in both directions between these entities, while the
Mobile Router is connected to a Visisted Link. The bi-directional
tunnel involves two virtual links [4]: one virtual link has the
address of the tunnel entry point as the Care-of Address of the
Mobile Router and the tunnel exit point as the address of the Home
Agent; the other virtual link has as tunnel entry point the Home
Agent address and as tunnel exit point the Care-of Address of the
Mobile Router. Both addresses are unicast addresses.
Packets sent by the nodes in the mobile network (including the Mobile
Router) and addressed to any nodes other than nodes in the mobile
network are encapsulated by Mobile Router and decapsulated by the
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Home Agent. Packets sent by any nodes other than nodes in the mobile
network and addressed to nodes in the mobile network are encapsulated
by the Home Agent and decapsulated by the Mobile Router.
A Mobile Router MAY limit the number of mobile routers that attach to
its mobile network (the number of levels in the nested aggregation)
by means of setting the Tunnel Encapsulation Limit field of the
Tunnel Encapsulation option.
A Mobile Router uses the Tunnel Hop Limit that is normally assigned
to routers (not to hosts); see IANA numbers.
Following the successful setup of the bi-directional tunnel on the
Mobile Router, the forwarding information on the Mobile Router is
updated such as to allow forwarding of packets as described above.
5.6. Neighbour Discovery for Mobile Router
A Mobile Router MAY be configured to send Router Advertisements and
reply to Router Solicitations on the interface attached to the home
link. The value of the Router Lifetime field MUST be set to zero to
prevent other nodes from configuring the Mobile Router as the default
router.
A Mobile Router SHOULD NOT send unsolicited Router Advertisements
and SHOULD NOT reply to Router Solicitations on any egress interface
when that interface is attached to any other link than the home link.
However, the Mobile Router SHOULD reply with Neighbor Advertisements
to Neighbor Solicitations received on the egress interface, for
topologically correct addresses.
A Mobile Router MAY use the received Router Advertisements on the
interface connected to the home link, but only for logging and
administrative purposes. Only when that interface is connected to
a visisted link, the Mobile Router uses information in the received
Router Advertisements for purposes other than logging; this includes
address configuration, setting up a default route and movement
detection.
5.7. Multicast Groups for Mobile Router
When at home, the Mobile Router joins the multicast group All Routers
Address with scopes '1' interface-local (on the home-advertising
interface), '2' link-local and '5' site-local on any of its egress
interfaces. When in a visited network, the Mobile Router MUST NOT
join any of the above groups on the respective interface.
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6. Home Agent Operation
In order for a Mobile Router to operate correctly, the home agent
MUST satisfy all the requirements listed in Section 8.4 of [1].
6.1. Prefix Table
In some scenarios, the Home Agent might need to maintain a Prefix
Table of Mobile Routers and the IPv6 prefixes owned by Mobile
Routers. The Home Agent MUST maintain this table if the Mobile
Routers operate under the implicit mode where they do not include any
prefix information in the Binding Updates.
Each entry in the Prefix Table conceptually contains the following
fields:
- The Home Address of the Mobile Router. This field is used as the
key for searching the pre-configured prefix table.
- The Mobile Network prefix of the Mobile Router associated with
the Home Address.
In some deployment scenarios it is important that the Home Agent
prevents a misbehaving Mobile Router from claiming Mobile Network
Prefixes belonging to another Mobile Router. The Home Agent can
prevent such attacks if it maintains the Prefix Table and verifies
the Prefix Information provided by the Mobile Router against the
entries in the Prefix Table.
6.2. Mobile Network Prefix Registration
The Home Agent processes the Binding Update as described in Section
10.3.1 of the Mobile IPv6 specification. This section describes the
processing of the Binding Update if the Mobile Router (R) flag is
set. The Home Agent performs the following check in addition.
- The Binding Update MUST be authenticated by IPsec according to
Section 5.1 of [1].
- The Home Registration (H) bit MUST be set. If not, the
Home Agent MUST reject the Binding Update and send a Binding
Acknowledgement with status set to 140. Note: The basic support
does not allow sending Binding Update for a Mobile Network prefix
to correspondent nodes (for route optimization)..
- If the Mobile Network Prefix Length option is present in
the Binding Update, then there MUST be only one instance of
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this option in the Binding Update. Also the Mobile Network
Prefix Option MUST not be present in the same Binding Update.
Otherwise, the Home Agent MUST discard the Binding Update and
send an ICMP Parameter Problem, Code 0, message to the Mobile
Router
If the home agent does not reject the Binding Update as described
above, then it retrieves the Mobile Network Prefix information as
described below.
- If a Mobile Network Prefix Length Option is present in the
Binding Update, the Home Address in the Home Address destination
option MUST be an extended Home Address. In that case, the
Mobile Network Prefix is obtained from that Home Address and the
prefix length in the Mobile Network Prefix Length Option.
If the Home Agent verfies the prefix information with the Prefix
Table and the check fails, the Home Agent MUST discard the
Binding Update and send a Binding Acknowldegement with status set
to 142 (Not Authorized for Prefix).
- If a Mobile Network Prefix Option is present in the Binding
Update, the prefix information for the mobile network prefix is
retrieved from the Mobile Network Prefix field and the Prefix
Length field of the option. If the Binding Update contains more
than one option, the Home Agent MUST set up forwarding for all
of the Mobile Network Prefixes. Otherwise the Home Agent MUST
not forward traffic to any of the prefixes, reject the Binding
Update and send a Binding Acknowledgement with status set to 141
(Invalid Prefix).
If the Home Agent verfies the prefix information with the Prefix
Table and the check fails, the Home Agent MUST discard the
Binding Update and send a Binding Acknowldegement with status set
to 142 (Not Authorized for Prefix).
- If there are no options in the Binding Update, the Home Agent
MUST figure out which prefixes are assigned to the Mobile Router
from the Pre-configured Prefix Table. If the home agent can not
find the correspondent Mobile Network prefix, it MUST reject the
Binding Update and send a Binding Acknowledgement with the Status
field set to 143 (Prefix Information unavailable).
If the Lifetime specified in the Binding Update is zero or the
specified care-of address matches the home address for the binding,
then this is a request to delete the cached binding for the home
address and specified mobile network prefixes. The Binding Update is
processed according to the procedure described in Section 6.7.
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If all checks are passed, the home agent creates a binding cache
entry for Mobile Router's home address, or updates the binding cache
entry if it already exists. Otherwise, the home agent MUST NOT
register the binding of the Mobile Router's home address.
The home agent also creates a bi-directional tunnel to the mobile
router for the requested Mobile Network prefix, or update an existing
bi-directional tunnel as described in Section 6.4
6.3. Advertising Mobile Network Reachability
In order to be able to receive packets meant for the Mobile Network,
the Home Agent advertises reachability to the Mobile Network. If the
Mobile Network Prefix can be aggregated under the Home Link prefix,
then the routing updates advertising reachability to the Mobile
Network are sent only on the Home Link. If the Home Agent is the
only router on the Home Link, routes to the Mobile Network Prefix
gets aggregated naturally under the Home Agent and the Home Agent
does not have to do anything special.
If the Home Agent receives routing updates through a dynamic routing
protocol from the Mobile Router, those routes are propogated by
the routing protocol running on the Home Agent on the relevant
interfaces.
6.4. Establishment of Bi-directional Tunnel
The establishment and operation of the bi-directional tunnel is
implementation specific. However, all implementations MUST be
capable of the following operations.
- The Home Agent can tunnel packets meant for the Mobile Network
Prefix to the Mobile Router's current location, the Care-of
Address of the Mobile Router.
- The Home Agent can accept packets tunneled by the Mobile Router
with source address of the outer IPv6 header set to the Care-of
Address of the Mobile Router.
6.5. Forwarding Packets
When the Home Agent receives a data packet destined for the mobile
network, it fowards the packet to the Mobile Router through the
bi-directional tunnel. The Home Agent either uses only the routing
table, only the Binding Cache or a combination of routing table
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and Binding Cache to route packets to the Mobile Network. This is
implementation specific. Two examples are shown below.
1. The Home Agent maintains a route to the Mobile Network Prefix
with the next hop set to the Mobile Router's Home Address. When
the Home Agent tries to forward the packet to the next hop, it
finds a binding cache entry for the home address. Then the Home
Agent extracts the Mobile Router's Care-of address and tunnels
the packet to the Care-of address.
2. The Home Agent maintains a route to the Mobile Network Prefix
with the outgoing interface set to the bi-directional tunnel
interface between the Home Agent and the Mobile Router. For
this purpose, the Home Agent MUST treat this tunnel as a tunnel
interface. When the packets are forwarded through the tunnel
interface, they get encapsulated automatically with the source
address and destination address in the outer IPv6 header set to
the Home Agent's address and the Mobile Router's Care-of address,
respectively.
6.6. Sending Binding Acknowledgements
A Home Agent serving a Mobile Router sends Binding Acknowledgements
according to the same rules it uses for sending Binding
Acknowledgements to Mobile Hosts, with the following enhancements.
The Home Agent sets the status code in the Binding Acknowledgement
to '0' (Binding Update accepted) in order to indicate to the Mobile
Router that it accepted the Binding Update, set up the tunnel
endpoint and the necessary forwarding information.
If the Home Agent is configured not to support mobile routers, it
sets the status code in the Binding Acknowledgement to '140' (Mobile
Router Operation not permitted).
If one or more prefixes received in the Binding Update are invalid
and the Home Agent cannot setup forwarding for the prefixes, the Home
Agent sets the status code in the Binding Acknowledgement to '141'
(Invalid Prefix) in order to indicate this to the Mobile Router.
If the Mobile Router is not authorized to use this Home Address to
forward packets for one or more prefixes that are present in the
Binding Update, the Home Agent sets the status code in the Binding
Acknowledgement to '142' (Not Authorized for Prefix) in order to
indicate this.
The Home Agent sets the status code in the Binding Acknowledgement
to '143' (Mobile Network Prefix information unavailable) in order
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to indicate the Mobile Router that the received Home Address in the
Binding Update does not match any prefix entry in the pre-configured
prefix table. This is used in the Implicit case where the Mobile
Router does not include any prefix information in the Binding Update.
6.7. Mobile Network Prefix De-Registration
The Mobile Router de-registers with the Home Agent by sending
a Binding Update with the lifetime set to zero. This Binding
Update MUST be secured as described in [3]. When the Home Agent
successfully processes the de-registration BU, it deletes the Binding
Cache Entry for the Mobile Router's Home Address and stops proxying
the Home Address. This is described in detail in the Mobile IPv6
specification [1].
In addition, the Home Agent also removes the bi-directional tunnel
and stops forwarding packets to the Mobile Network.
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7. Extended Home Network
With MIPv6, the Home Network is generally a physical network
interconnecting the Home Agents, and the Mobile Nodes that are at
Home. The Network Mobility concept introduces the extended Home
Network that aggregates the Home Network(s) and the Mobile Network(s)
in a single, shorter prefix.
For most practical situations, it is expected that:
- There is a single Home Network and multiple Mobile Networks
- The Home Network and Mobile Network prefixes are tailored to
allow for IPv6 Stateless Address Autoconfiguration with typical
interface identifier length for the type of interface.
- The prefix length of the extended Home Network is shorter than
the Home Network and the Mobile Network prefixes, since it is an
aggregation.
- The Home Agents collectively advertise the extended Home Network
aggregation only. The dichotomy of the extended Home Network is
kept within the Home Agents and the Mobile Nodes, as opposed to
advertised by means of routing protocols to other parties.
The Home Network is configured on a physical interface as defined in
MIPv6. A Mobile Router may own a Home Address that is built out of
the Home Network prefix and use it for Nemo registration and to come
back Home. In that case, the Home Network Prefix and prefix length
are used in the Binding Update.
A Mobile Router owns one or several Mobile Networks. It may form
extended Home Addresses from the prefixes of its Mobile Network(s)
and register them to the Home Agent using the extended Home Network
prefix and prefix length. An extended Home Address may be used for
only one registration that it identifies uniquely, regardless of the
Home Agent, as for normal Home Addresses.
An extended Home Network may be configured on a virtual or a physical
interface of the Home Agent. It is partitioned in Mobile Networks
and Home Networks. If the extended Home Network is configured on a
physical Network, a Mobile Router that registers using an extended
Home Address may come back home by:
- Autoconfiguring a Care-of Address from the Home Network and
providing Proxy Neighbor Discovery for its Mobile Network
Prefixes
or
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- Attaching directly by its Ingress Link if it has only one of
them.
Multihoming, and in particular the associated coordination of
the Home Agents, is out of the scope of this document. Yet, this
specification does not prevent that:
- More than one Mobile Network may be connected to a Mobile Router
- A Mobile Network Prefix may be shared between Mobile Routers and
registered by some of them
- An Mobile Network Prefix may be registered several times to
several Home Agents using different (extended) Home Addresses for
each registration.
This description is open to a:
- Mobile Router autoconfiguring one or several extended Home
Address to carry out many registrations in parallel. It owns the
full prefix so it may use any address in there for a MNLP based
registration, and several of them for multihoming.
- Mobile Node autoconfiguring one or several Care-of Addresses from
the Mobile Network Prefix
- Mobile Host autoconfiguring one or several Home Addresses from
the Home Network.
Mobile Nodes' Home Addresses may still be configured manually from
the Home Network Prefix as described in Mobile IPv6.
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8. Support for Dynamic Routing Protocols
In the solution described so far, forwarding to the Mobile Network
at the Home Agent is set up when the Home Agent receives a Binding
Update from the Mobile Router. An alternative to this is for the
Home Agent and the Mobile Router to run a intra-doamin routing
protocol like RIPng [6] and OSPF [7] through the bi-directional
tunnel. The Mobile Router can continue running the same routing
protocol that it was running when it was attached to the home link.
This feature is very useful when the Mobile Network is large with
multiple subnets containing different IPv6 prefixes. Routing changes
in the Mobile Network are propagated to the Home Agent quickly.
Routing changes in the home link are also propogated to the Mobile
Router very quickly.
When the Mobile Router is attached to the home link, it runs a
routing protocol by sending routing updates through its egress
interface. When the mobile router moves and attaches to a visited
network, it MUST stop sending routing updates on the interface with
which it attaches to the visited link. This is very important so
that IPv6 prefixes specific to the Mobile Network do not leak into
the visited network. The Mobile Router then starts sending routing
protocol messages through the bi-directional tunnel towards the Home
Agent. Most routing protocols use link local addresses as source
addresses for the routing information messages. The Mobile Router is
allowed to use link local addresses for the inner IPv6 header of an
encapsulated packet. But these messages after decapsulation MUST NOT
be forwarded to another link by either the Mobile Router or the Home
Agent.
When the Home Agent receives the encapsulated routing protocol
message, it processes the inner packets and updates its routing table
accordingly. The next hop information in these routing entries is
filled with the Mobile Router's link local address with the outgoing
interface set to the bi-directional tunnel.
Similary, the Home Agent also sends routing updates through the
bi-directional tunnel to the Mobile Router. The Mobile Router
processes these routing protocol messages and updates its routing
table. For all routes advertised by the Home Agent, the Mobile
Router sets the outgoing interface to the bi-directional tunnel to
the Home Agent.
The tunneled routing messages MUST be authenticated and encrypted by
using IPsec ESP [5] in tunnel mode.
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9. Use of IPsec to protect the Signaling Messages
The use of IPsec to protect to Mobile IPv6 signaling messages is
described in detail in HA-MN IPsec specification [3]. This document
does not require any changes or anything more that what is described
in the HA-MN IPsec specification.
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10. Security Considerations
The Home Agent has to verify that packets received through the
bi-directional tunnel belong to the Mobile Network. This check is
necessary in order to prevent nodes from using the Home Agent to
launch attacks that would have otherwise been prevented by ingress
filtering. The source address of the outer IPv6 header MUST be set
the Mobile Router's current Care-of address. The source address of
the inner IPv6 header MUST belong to the Mobile Network Prefix owned
by the Mobile Router.
When the Mobile Router is running a dynamic routing protocol as
described in Section 8, it injects routing update messages into the
Home Link. The Home Agent MUST verify that the Mobile Router is
allowed to send routing updates before processing the messages and
propagating the routing information.
Please refer to the Mobile IPv6 specification [1] for security
considerations when the Mobile Router operates as a Mobile Host.
11. IANA Considerations
This document defines two new Mobility Header Options.
- Mobile Network Prefix Option
- Mobile Network Prefix Length Option.
These options are described in section 4.3 and section 4.4. The type
values for these options need to assigned from the same space used by
the mobility options defined in [1]
12. Contributors
We would like to acknowledge Thierry Ernst, Miguel Catalina-Gallego,
Christophe Janneteau, T.J. Kniveton, Hong-Yon Lach, Jari T. Malinen,
Koshiro Mitsuya, Charles E. Perkins and Keisuke Uehara, for their
work on earlier proposals for Network Mobility. This document
inherits a lot of ideas from these earlier proposals.
13. Acknowledgements
We also thank all members of the NEMO Working Group, and of the
preceding MONET BoF for fruitful discussions on the mailing list and
at IETF meetings.
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Tim Leinumeller for many insightful remarks and implementation
aspects.
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References
[1] D. Johnson, C. Perkins and J. Arkko. Mobility Support
in IPv6 (work in progress). Internet Draft, IETF.
draft-ietf-mobileip-ipv6-22.txt. May 2003.
[2] T. Ernst and H.-Y. Lach. Network Mobility Support
Terminology (work in progress). Internet Draft, IETF.
draft-ietf-nemo-terminology-00.txt. May 2003.
[3] J. Arkko, V. Devarapalli and F. Dupont. Using IPsec to
Protect Mobile IPv6 Signaling between Mobile Nodes and
Home Agents (work in progress). Internet Draft, IETF.
draft-ietf-mobileip-mipv6-ha-ipsec-05.txt May 2003.
[4] A. Conta and S. Deering. Generic Packet Tunneling in IPv6
Specification. RFC 2473, IETF. December 1998.
[5] S. Kent and R. Atkinson. IP Encapsulating Security Payload (ESP).
RFC 2402, IETF. November 1998.
[6] G. Malkin and R. Minnear. RIPng for IPv6. RFC 2080, IETF. January
1997.
[7] R. Coltun, D. Ferguson and J. Moy. OSPF for IPv6. RFC 2470, IETF.
December 1999.
[8] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification. RFC 2460, IETF. December 1998.
[9] T. Narten, E. Nordmark and W. Simpson. Neighbour Discovery for IP
Version 6 (IPv6). RFC 2461, IETF. December 1998.
[10] C. Perkins, ed. IP Mobility Support for IPv4. RFC 3344, IETF.
August 2002.
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A. Examples of Operation
This section tries to illustrate the NEMO protocol using a Mobile
Router and a Mobile Node belonging to different administrative
domains. The Mobile Router's mobile network consists of a Local
Fixed Node (LFN) and a Local Fixed Router (LFR) [2]. The LFR has
an access link to which other Mobile Nodes or Mobile Routers could
attach to.
Figure 1 depicts the scenario where both the Mobile Router and the
Mobile Node are at home.
+----+ +-------+
| MN | | HA_MN |
+--+-+ 1:: +---+---+
2+-------------+3
|
|
+-------+2 2:: +-------------------+ 3:: 2+-------+
| CN_MN |------| Internet |------| CN_MR |
+-------+ +-------------------+ +-------+
4:: |
|
2+-------------+3
+--+-+ +---+---+
| MR | | HA_MR |
+--+-+ +-------+
5:: |1
----------
2| |3
+--+-+ +--+-+
| LFN| | LFR|
+--+-+ +--+-+
6:: |1
----------
Figure 1: Mobile Router and Mobile Node at home.
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The Mobile Router then moves away from the home link and attaches to
a visited link. This is shown in Figure 2. The Mobile Router sends
a Binding Update to HA_MR when it attaches to a visited link and
configures a Care-of Addres. HA_MR creates a binding cache entry for
the Mobile Router's Home Address and also sets up forwarding for the
prefixes on the mobile network.
+----+ +-------+
| MN | | HA_MN |
+--+-+ 1:: +---+---+
2+-------------+3
|
|
+-------+2 2:: +-------------------+ 3:: 2+-------+
| CN_MN |------| Internet |------| CN_MR |
+-------+ ++------------------+ +-------+
| 7:: 4:: | 4::2->7::2
| |
2+ +3
+--+-+ +---+---+
| MR | | HA_MR | 4::2->7::2
+--+-+ +-------+ 5::/prefixlen -> forward
5:: |1 to MR
---------- 6::/prefixlen -> forward
2| |3 to MR
+--+-+ +--+-+
| LFN| | LFR|
+--+-+ +--+-+
6:: |1
----------
Figure 2: Mobile Router on a Visited Link.
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Figure 3 shows the Mobile Node moving away from its home link and
attaching to the Mobile Router. The Mobile Node configures a Care-of
Address from the prefix advertised on the mobile network and sends a
Binding Update to its Home Agent (HA_MN) and its Correspondent Node
(CN_MN). Both HA_MN and CN_MN create binding cache entries for the
Mobile Node's Home Address.
+-------+
| HA_MN | 1::2->6::2
1:: +---+---+
---------|3
|
|
+-------+2 2:: +-------------------+ 3:: 2+-------+
| CN_MN |------| Internet |------| CN_MR |
+-------+ ++------------------+ +-------+
3::2->6::2 | 7:: 4:: | 4::2->7::2
| |
2+ +3
+--+-+ +---+---+
| MR | | HA_MR | 4::2->7::2
+--+-+ +-------+ 5::/prefixlen -> forward
5:: |1 to MR
---------- 6::/prefixlen -> forward
2| |3 to MR
+--+-+ +--+-+
| LFN| | LFR|
+--+-+ +--+-+
6:: |1
--------+-
|2
+--+-+
| MN |
+----+
Figure 3: Mobile Node attached to Mobile
Router on a Visited Link
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Authors Addresses
Vijay Devarapalli
Nokia Research Center
313 Fairchild Drive
Mountain View, CA 94043
USA
Email: vijay.devarapalli@nokia.com
Ryuji Wakikawa
Keio University and WIDE
5322 Endo Fujisawa Kanagawa
252-8520 Japan
Email: ryuji@sfc.wide.ad.jp
Alexandru Petrescu
Motorola Labs
Espace Technologique de St Aubin
Gif-sur-Yvette 91193
France
Email: Alexandru.Petrescu@motorola.com
Pascal Thubert
Cisco Systems Technology Center
Village d'Entreprises Green Side
400, Avenue Roumanille
Biot - Sophia Antipolis 06410
France
Email: pthubert@cisco.com
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Full Copyright Statement
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Devarapalli, et al. Expires 21 December 2003 [Page 35]
