NEMO Working Group Vijay Devarapalli
INTERNET DRAFT Nokia
Category: Standards Track Ryuji Wakikawa
Expires March 2004 Keio University
Alexandru Petrescu
Motorola
Pascal Thubert
Cisco Systems
September 2003
Nemo Basic Support Protocol
draft-ietf-nemo-basic-support-01.txt
Status of This Memo
This document is an Internet-Draft and is subject to all provisions
of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at
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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 the Nemo Basic Support protocol to support
network mobility as the mobile network attaches to different points
in the Internet. The protocol is based on extensions to Mobile
IPv6 and 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 Mobile
Router, which connects the network to the Internet, runs the NEMO
Basic Support 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 6
4. Message Formats 9
4.1. Binding Update . . . . . . . . . . . . . . . . . . . . . 9
4.2. Binding Acknowledgement . . . . . . . . . . . . . . . . . 9
4.3. Mobile Network Prefix Option . . . . . . . . . . . . . . 10
4.4. Mobile Network Prefix Length Option . . . . . . . . . . . 11
5. Mobile Router Operation 13
5.1. Data Structures . . . . . . . . . . . . . . . . . . . . . 13
5.2. Sending Binding Updates . . . . . . . . . . . . . . . . . 13
5.3. Receiving Binding Acknowledgements . . . . . . . . . . . 14
5.4. Error Processing . . . . . . . . . . . . . . . . . . . . 15
5.5. Establishment of Bi-directional Tunnel . . . . . . . . . 16
5.6. Neighbour Discovery for Mobile Router . . . . . . . . . . 17
5.7. Multicast Groups for Mobile Router . . . . . . . . . . . 17
6. Home Agent Operation 18
6.1. Data Structures . . . . . . . . . . . . . . . . . . . . . 18
6.1.1. Binding Cache . . . . . . . . . . . . . . . . . . 18
6.1.2. Prefix Table . . . . . . . . . . . . . . . . . . 18
6.2. Mobile Network Prefix Registration . . . . . . . . . . . 19
6.3. Advertising Mobile Network Reachability . . . . . . . . . 20
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 . . . . . . . . . . 22
7. Support for Dynamic Routing Protocols 23
8. Security Considerations 25
9. IANA Considerations 25
10. Contributors 25
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11. Acknowledgements 26
A. Examples of Operation 28
B. Changes from Previous Version 31
Addresses 32
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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
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 [8] and Mobile Nodes in the Mobile Network.
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.
The terminology document [8] 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 significant overhead on
the data packets as each level of nestedness introduces another IPv6
header encapsulation.
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2. Terminology
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].
There is a separate NEMO terminology document [8], which defines the
terms related to Network Mobility used in the document.
Prefix Table
It is a list of a Mobile Network Prefixes indexed
by the Home Address of a Mobile Router. The prefix table
is managed by the Home Agent and is used by the Home Agent
to determine which Mobile Network Prefixes are owned
a particular Mobile Router. This is an optional data
structure.
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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. 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. 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.
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, reachability 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 MAY
also include 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
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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 with the router flag 'R' set.
The Home Agent acknowledges the Binding Update by sending a Binding
Acknowledgement to the Mobile Router. A positive acknowledgement
means that the HA has set up forwarding for the Mobile Network.
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 [3].
The Home Agent decapsulates this packet and forwards it to the
Correspondent Node. 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. 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 interface where the Mobile
Network is connected. The Mobile Router before decapsulating the
tunneled packet, has to check if the Source address on the outer IPv6
header is the Home Agent's address. It also has to make sure the
destination address on the inner IPv6 header belongs to one of its
Mobile Network Prefixes before forwarding the packet to the Mobile
Network.
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The Mobile Network could consist of nodes which are Local Fixed
Nodes, Local Mobile Nodes and Visiting Mobile Nodes [8]. The
protocol described here ensures complete transparency of network
mobility to the Local Fixed Nodes. Visiting Mobile Nodes are those
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. In that case,
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 configured not to run the routing protocol on its egress
interface when it is away from the home link.
Finally, the Home Agent may be configured with static routes to the
Mobile Network Prefix via the Mobile Router's 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 related 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 MUST 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 in [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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2 Mobile Router Binding Update accepted
140 Mobile Router Operation not permitted
141 Invalid Prefix
142 Not Authorized for Prefix
143 Forwarding Setup failed
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
TBA
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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
This field is unused for now. The value MUST be initialized to
zero by the sender, and MUST be ignored by the receiver.
Prefix Length
8 bit unsigned integer indicating the prefix 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
TBA
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
This field is unused for now. The value MUST be initialized to
zero by the sender, and MUST be ignored by the receiver.
Prefix Length
8 bit unsigned integer indicating the prefix length of the IPv6
prefix from which the Home Address included in the Binding
Update was configured.
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5. Mobile Router Operation
Mobile Router operation is derived largely from the combined
behaviors of a Host, of a Router [6], and of a Mobile Node [1] (also
please see definition of a Mobile Host in [8]).
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 Mobile Router flag 'R'.
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 Mobile Router flag 'R' 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 stores the information
regarding status of flags of the Binding Update, in the corresponding
Binding Update List entry. 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.
A Mobile Router also maintains a Home Agent list populated according
to the same procedure as a Mobile Host.
5.2. Sending Binding Updates
A Mobile Router sends Binding Updates to its Home Agent according to
the same procedures that a Mobile Host uses. The Mobile Router uses
one of the following modes to instruct the Home Agent to determine
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the prefixes owned by the Mobile Router. In all three modes, the
Mobile Router sets the Mobile Router flag 'R'.
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 by the Mobile Router and setup forwarding for the Mobile
Network. One example would be manual configuration at the
Home Agent mapping the Mobile Router's Home Address to the
information required for setting up forwarding for the Mobile
Network.
Explicit Network:
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 Prefix Length:
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, Home Registration flag 'H' MUST be
set.
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 Acknowledgement status is set to '2' (Mobile Router Binding
Update accepted), the Mobile Router assumes that the Home Agent has
successfully processed the Binding Update and has set up forwarding
for the Mobile Network.The Mobile Router can then start using the
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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 Binding Acknowlegement status is set to '0' (Binding Update
accepted), the Mobile Router concludes that the Home Agent which
processed the Binding Update is a MIPv6 Home Agent that has not
implemented support for Mobile Routers. It should send a similar
Binding Update to another Home Agent on the link. If no Home Agent
replies positively then the Mobile Router MUST refrain from sending
any Binding Update with the Mobile Router flag set to any home agent
on the home link and log the information.
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'
(Forwarding Setup failed) For this Binding Update, the Mobile Router
MUST discard Binding Acknowledgements with codes '141' and '142'.
For the same Binding Update, if the status is '140', then the 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 Mobile Router flag set to any Home Agent on
the home link, and log the information.
For the same Binding Update, if the status is '143', then the 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 MUST discard
Binding Acknowledgements with codes '140' and '143'.
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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 lengths) 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. At this point, Mobile Router MAY 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 value
between 0 and 127) for this Home Address from any Home Agent on its
home link, then the Mobile Router MUST stop sending Binding Updates
with the Mobile Router flag set for this Home Address and log the
information.
In all the above cases, the Mobile Router MUST conclude 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
When a successful Binding Acknowledgement with status set to '2'
(Mobile Router Binding Update accepted) is received, 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 Visited Link. The bi-directional
tunnel involves two virtual links [3]: 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
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Home Agent address and as tunnel exit point the Care-of Address
of the Mobile Router. Both addresses are unicast addresses. All
IPv6 traffic to and from the Mobile Network is sent through this
bi-directional tunnel.
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 [3].
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 a visited 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 MUST NOT ignore Router Advertisements received on
the egress interface. The received Router Advertisements MAY be
used for address configuration, default router selection or 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) and '2' link-local on any of its egress interfaces. When
in a visited network, the Mobile Router MUST NOT join the above
multicast groups on the corresponding 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]. The
Home Agent MUST implement all the modes described in Section 5.2.
6.1. Data Structures
6.1.1. Binding Cache
The Home Agent maintains Binding Cache Entries for each Mobile Router
that is currently registered with the Home Agent. The Binding Cache
is a conceptual data structure described in detail in [1].
The Home Agent might need to store the Mobile Network Prefixes
associated with a Mobile Router in the corresponding Binding Cache
Entry. This is required if the Binding Update (that created the
Binding Cache Entry) contained explicit prefix information. This
information can be used later to cleanup routes installed in explicit
mode, when the Binding Cache Entry is removed, and to maintain the
routing table, for instance should the routes be manually removed.
The Home Agent also stores the status of the Mobile Router Flag 'R'
in the Binding Cache entry.
6.1.2. Prefix Table
In some deployment scenarios it may be necessary for the Home Agent
to prevent a misbehaving Mobile Router from claiming mobile network
prefixes belonging to another Mobile Router. The Home Agent can
prevent such attacks if it maintains a Prefix Table and verifies the
Prefix Information provided by the Mobile Router against the entries
in the Prefix Table. However, this verification is done only if the
Binding Update contained explicit prefix information in the form of
either the Mobile Network Prefix Option or the Mobile Network Prefix
Length Option.
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.
Devarapalli, et al. [Page 18]
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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 [1]. 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 Home Registration (H) flag 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
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 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. If the Home Agent fails to setup
forwarding to all the prefixes listed in the Binding Update, then
it 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 verifies the prefix information with the Prefix
Table and the check fails, the Home Agent MUST discard the
Devarapalli, et al. [Page 19]
Internet Draft Nemo Basic Support September 2003
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
uses manual pre-configured information to determine the prefixes
assigned to the Mobile Router and for setting up forwarding for
the Mobile Network. If there is no information that the Home
Agent can use, it MUST reject the Binding Update and send a
Binding Acknowledgement with status set to 143 (Forwarding Setup
failed).
If the Lifetime specified in the Binding Update is zero or the
specified Care-of address matches the Home Address in the Binding
Update, 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.
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 defends the Mobile Router's Home Address through Proxy
Neighbor Discovery by multicasting onto the home like a Neighbor
Advertisement message on behalf of the mobile router. All fields in
each such Neighbor Advertisement message SHOULD be set in the same
way they would be set by the mobile router itself if sending this
Neighbor Advertisement while at home, as described in [7], with the
exception that the Router (R) bit in the Advertisement MUST be set if
the Mobile Router (R) flag has been set in the Binding Update.
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
Home Link is configured with a prefix that is an aggregation and if
the Mobile Network Prefix is aggregated under that 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 default
router on the Home Link, routes to the Mobile Network Prefix get
aggregated naturally under the Home Agent and the Home Agent does not
have to do anything special.
Devarapalli, et al. [Page 20]
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If the Home Agent receives routing updates through a dynamic routing
protocol from the Mobile Router, those routes are propagated 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
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.
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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 '2' (Mobile Router 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 to 143 (Forwarding Setup
failed) if it is unable to determine the information needed to setup
forwarding for the Mobile Network. This is used in the Implicit mode
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. 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. The HA should
keep all necessary information to clean up whichever routes it
installed, whether they come from implicit or explicit source.
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7. 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-domain routing
protocol like RIPng [10] and OSPF [11] 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.
When the Mobile Router and the Home Agent exchange routes through
a dynamic routing protocol, the Mobile Router should be careful in
including the same mobile network prefixes in the Binding Update to
the HA and in the routing protocol updates. The HA depending on its
configuration might not add routes based on the prefix information in
Devarapalli, et al. [Page 23]
Internet Draft Nemo Basic Support September 2003
the Binding Updates at all, and might use only the routing protocol
updates. Moreover, including the same prefix information in both the
Binding Update and the routing protocol update is redundant.
The tunneled routing messages MUST be authenticated and encrypted by
using IPsec ESP [4] in tunnel mode.
Devarapalli, et al. [Page 24]
Internet Draft Nemo Basic Support September 2003
8. Security Considerations
All signaling messages between the Mobile Router and the Home Agent
MUST be authenticated by IPsec [5]. The use of IPsec to protect
Mobile IPv6 signaling messages is described in detail in the HA-MN
IPsec specification [2]. The signaling messages described in this
document just extend Mobile IPv6 messages and do not require any
changes to what is described in the HA-MN IPsec specification.
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 7, 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.
9. 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]
10. Contributors
We would like to acknowledge Ludovic Bellier, Claude Castelluccia,
Thierry Ernst, Miguel Catalina-Gallego, Christophe Janneteau, T.J.
Kniveton, Hong-Yon Lach, Jari T. Malinen, Koshiro Mitsuya, Alexis
Olivereau, Charles E. Perkins and Keisuke Uehara, for their work on
earlier proposals for Network Mobility. This document inherits a lot
of ideas from these proposals.
Devarapalli, et al. [Page 25]
Internet Draft Nemo Basic Support September 2003
11. Acknowledgements
We 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.
Kent Leung, Marco Molteni and Patrick Wetterwald for their work on
Network Mobility for IPv4 and IPv6.
Tim Leinmueller for many insightful remarks and implementation
aspects.
Devarapalli, et al. [Page 26]
Internet Draft Nemo Basic Support September 2003
Normative References
[1] D. Johnson, C. Perkins and J. Arkko. Mobility Support in IPv6.
Internet Draft, IETF. draft-ietf-mobileip-ipv6-24.txt (work in
progress). June 2003.
[2] J. Arkko, V. Devarapalli and F. Dupont. Using IPsec to Protect
Mobile IPv6 Signaling between Mobile Nodes and Home Agents.
Internet Draft, IETF. draft-ietf-mobileip-mipv6-ha-ipsec-06.txt
(work in progress). June 2003.
[3] A. Conta and S. Deering. Generic Packet Tunneling in IPv6
Specification. RFC 2473, IETF. December 1998.
[4] S. Kent and R. Atkinson. IP Encapsulating Security Payload
(ESP). RFC 2402, IETF. November 1998.
[5] S. Kent and R. Atkinson. Security Architecture for the Internet
Protocol. RFC 2401, IETF. November 1998.
[6] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification. RFC 2460, IETF. December 1998.
[7] T. Narten, E. Nordmark and W. Simpson. Neighbour Discovery for
IP Version 6 (IPv6). RFC 2461, IETF. December 1998.
Informative References
[8] T. Ernst and H.-Y. Lach. Network Mobility Support Terminology.
Internet Draft, IETF. draft-ietf-nemo-terminology-00.txt (work
in progress). May 2003.
[9] T. Ernst. Network Mobility Support Goals and Requirements.
Internet Draft, IETF. draft-ietf-nemo-requirements-01.txt (work
in progress). May 2003.
[10] G. Malkin and R. Minnear. RIPng for IPv6. RFC 2080, IETF.
January 1997.
[11] R. Coltun, D. Ferguson and J. Moy. OSPF for IPv6. RFC 2470,
IETF. December 1999.
Devarapalli, et al. [Page 27]
Internet Draft Nemo Basic Support September 2003
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) [8]. 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.
Devarapalli, et al. [Page 28]
Internet Draft Nemo Basic Support September 2003
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.
Devarapalli, et al. [Page 29]
Internet Draft Nemo Basic Support September 2003
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 |
+-------+ ++------------------+ +-------+
1::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
Devarapalli, et al. [Page 30]
Internet Draft Nemo Basic Support September 2003
B. Changes from Previous Version
The following changes have been made to this document from version 00
- Clarified that Router flag must be set in the Proxy Neighbor
Advertisement sent for a Mobile Router by the Home Aagent.
(Issue 1).
- Clarified that if the Router flag in the Binding Update is set,
then the HA should assume that the Mobile Router wants to be
treated as a mobile node. (Issue 3).
- Added text to make it clear that the Home Agent must perform
ingress filtering on all packets reverse tunneled by the Mobile
Router. (Issue 3).
- Extended Home Network concept has been removed from this
document. (Issue 5).
- Added text to clarify differences between Implicit mode and
running a dynamic routing protocol. (Issue 6).
- Clarified that Prefix Table is used only in explicit mode. In
Implicit mode the Prefix Table is not used. (Issue 7 and 12).
- Added text to specify the Home Agent must support all modes. The
Mobile Router needs to support only one mode. (Issue 11).
- Added text to support interoperability between a Mobile Router
and a legacy MIPv6 Home Agent. (Issue 15).
Devarapalli, et al. [Page 31]
Internet Draft Nemo Basic Support September 2003
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
Parc les Algorithmes Saint 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
Devarapalli, et al. [Page 32]
Internet Draft Nemo Basic Support September 2003
Full Copyright Statement
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Devarapalli, et al. [Page 33]
