NEMO Working Group Ryuji Wakikawa
INTERNET DRAFT Keio University/WIDE
Category: Standards Track Vijay Devarapalli
20 Oct 2003 Nokia
Pascal Thubert
Cisco Systems
Inter Home Agents Protocol (HAHA)
draft-wakikawa-mip6-nemo-haha-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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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:
http://www.ietf.org/shadow.html.
Abstract
This document describes an inter Home Agents (HAHA) protocol to
provide multiple Home Agents support for both Mobile IPv6 and the
Nemo Basic Support protocol. The HAHA protocol provides Home Agent
redundancy and load-balancing for both protocols. The HAHA protocol
allows multiple Home Agents to be placed at different links. It
also allows a Mobile Node/Router to utilize multiple Home Agents
simultaneously. The protocol consists of 3 mechanisms, Home Agent
List management, Binding Synchronization, and Home Agent Switching.
A Mobile Node/Router picks one Home Agent as its primary Home Agent
and registers with it. The primary Home Agent synchronizes the
binding cache information with other Home Agents. Any of Home Agents
can intercept a packet meant for the Mobile Node/Router and tunnel
the packet directly to its current Care-of address. Alternatively,
the Home Agent can tunnel the packet to the primary Home Agent.
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Contents
Status of This Memo 1
Abstract 1
1. Introduction 4
2. Terminology 6
3. Overview of Inter Home Agents Protocol 7
4. Message Formats 9
4.1. New ICMP Messages . . . . . . . . . . . . . . . . . . . . 9
4.1.1. Home Agent Solicitation Message . . . . . . . . . 9
4.1.2. Home Agent Advertisement Message . . . . . . . . 10
4.2. New Mobility Header Messages . . . . . . . . . . . . . . 11
4.2.1. Binding Information Request Message . . . . . . . 11
4.2.2. Binding Information Reply Message . . . . . . . . 12
4.2.3. Home Agent Switch Request Message . . . . . . . . 12
4.3. New Mobility Options . . . . . . . . . . . . . . . . . . 13
4.3.1. Home Address . . . . . . . . . . . . . . . . . . 13
4.3.2. Mobile Network Prefix Option . . . . . . . . . . 14
4.3.3. Binding Cache Entry Information Option . . . . . 14
5. Home Agent Lists Management 16
5.1. Requesting Home Agent Information . . . . . . . . . . . . 16
5.2. Notifying Home Agent Information . . . . . . . . . . . . 16
6. Binding Synchronization among Home Agents 17
6.1. Requesting Binding . . . . . . . . . . . . . . . . . . . 17
6.2. Notifying Binding . . . . . . . . . . . . . . . . . . . . 17
7. Primary Home Agent Switching 18
7.1. Home Agent initiated Switching . . . . . . . . . . . . . 19
7.2. Mobile Router initiated Switching . . . . . . . . . . . . 19
8. Scenarios 20
8.1. Solo Home Agent Activation . . . . . . . . . . . . . . . 20
8.2. Multiple Home Agent Activation . . . . . . . . . . . . . 21
9. Modifications to Mobile IPv6 and the Nemo Basic Support Protocol 24
10. IANA Considerations 26
11. Security Considerations 26
A. Predictive HA discovery 28
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Addresses 33
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1. Introduction
In Mobile IPv6 [1], a Mobile Node could be tunneling and receiving
all its traffic through a bi-directional tunnel with its Home Agent,
unless it uses Route Optimization with its Correspondent Nodes. In
Nemo Basic Support protocol [6], the default mode of operation is
to tunnel all traffic meant for the Mobile Network through the Home
Agent serving the Mobile Router. Consequently, Home Agents could
become a considerable bottleneck in the performance of Mobile IPv6
and Nemo protocols. This becomes more significant when the Home
Agent serves thousands of Mobile Node and Mobile Routers. Sometimes
the Mobile Network could be closer to the Correspondent Node than
the Home Agent. If the Mobile Router could pick another Home Agent
closer to its current location, the tunneling overhead on every
packet could be reduced to a much shorter path in the Internet.
This draft specifies the inter Home Agents protocol (HAHA protocol)
to provide redundancy and load balancing of Home Agents. For the
HAHA protocol, the definition of Home Agent is extended to place
multiple Home Agents at different links. Multiple Home Agents could
be located on different links and still serve the same home prefix.
Mobile IPv6 uses a IPv6 Neighbor Discovery based mechanism for
maintaining the list of Home Agents serving the same prefix, at each
Home Agent. If the Home Agents are not present on the same physical
link, Neighbor Discovery based mechanisms don't work. The HAHA
protocol defines a mechanism for Home Agents List management using
new ICMP messages for Home Agents located on different links.
The HAHA protocol makes it possible to have two new scenarios which
would not have possible with Mobile IPv6 and the Nemo Basic Support
Protocol. These scenarios are Solo Home Agent Activation and
Multiple Home Agent Activation and are explained in the following
paragraphs.
In the scenario of Solo Home Agent activation, a Mobile Router always
selects the best Home Agent to register its binding depending on
Mobile Router's current location or Home Agent status. For example,
when a Mobile Router registers its binding to the nearest Home Agent,
the path between the Mobile Router and the Home Agent can be the
shortest possible path. This is particularly useful for a Mobile
Router which moves over geographically wide areas such as a Mobile
Router on an airplane.
In the scenario of Multiple Home Agent activation, a Mobile
Node/Router registers its binding to multiple Home Agents at the same
time. The Mobile Router sends a binding update to its primary home
agent. After the home registration, the primary Home Agent exchanges
the binding information with the other Home Agents. Thereafter, the
Mobile Node/Router can use any of these Home Agents which have the
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binding. The Mobile Router can accept packets which are tunneled by
any of the Home Agents. Alternatively, a Home Agent who intercepts
packets can tunnel packets to the primary Home Agent. In this case,
the Mobile Router receives packets through the primary Home Agent.
If many Home Agents are scattered on the Internet, the Home Agent
nearest to the correspondent node intercepts packets meant for the
Mobile Node or the Mobile Network and tunnels them to the Mobile
Node/Router. The route path between the correspondent node and the
Home Agent can be kept short.
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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.
Home Agent
A Home Agent is originally defined in [1]. Traditional
Home Agents, if they all serve the same home prefix are
configured on a single link. This document extends the
definition of Home Agents such that the Home Agents need
not be on the same link. There could be multiple Home
Agents attached to different links serving the same home
prefix.
Primary Home Agent
A Home Agent who receives Binding Update from a Mobile
Router. The Mobile Router is always associated with a
primary Home Agent to register its binding.
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3. Overview of Inter Home Agents Protocol
When multiple Home Agents are configured at different links, each
home agent is expected to know the other Home Agents beforehand and
establishes Security Association with them for a secure path towards
the other home agent.
Each Home Agent manages information of all Home Agents in its Home
Agent list. But each Home Agent can not listen Router Advertisements
sent by the other Home Agents configured at different link, because
Router Advertisements can not be sent over the link-local scope.
Therefore, each Home Agents periodically unicasts a Home Agent
Advertisement message instead of Router Advertisement to the
other Home Agents configured at different links. The Home Agent
Advertisement message MUST be sent with the ICMP Prefix Information
Option and the ICMP Home Agent Information Option defined in [1].
Whenever a Home Agent receives a Home Agent Advertisement message, it
updates its home agent list according to the received message. The
Home Agent proceeds the Home Agent Advertisement as same as when it
receives Router Advertisements with the H bit flag. The Home Agent
manages the home agent list as same as the Mobile IPv6 specification.
If the lifetime of an entry is expired in the home agent list, the
Home Agent should solicit a Home Agent Advertisement message by
unicasting a Home Agent Solicitation message.
Binding synchronization of a particular Mobile Node/Router can
activate multiple Home Agents simultaneously. When a primary
Home Agent receives a Binding Update and creates a binding, it
notifies the binding to the other Home Agents by unicasting Binding
Information Reply messages. Home Agents receiving the Binding
Information Reply message records binding information and the address
of the primary home agent into their binding cache. A Home Agent
sends a Binding Information Request message to solicit a Binding
Information Reply message to the primary Home Agent if needed.
When a Home Agent wants a Mobile Router to change the primary Home
Agent, it sends a Home Agent Switch Request message to trigger the
Dynamic Home Agent Address Discovery to a Mobile Node/Router. After
receiving an ICMP Home Agent Address Discovery Request, the Home
Agent should reply an ICMP Home Agent Address Discovery Reply with
addresses of appropriate Home Agent addresses. If the Home Agent
has already had the desired new primary Home Agent, it contains
the address of the new Home Agent in the Home Agent Switch Request
message. The Mobile Router switches its primary Home Agent to the
new Home Agent. When the Mobile Node/Router changes the primary Home
Agent proactively, it selects a new Home Agent from its home agent
list. After determination of the new Home Agent, it simply registers
its binding to the new Home Agent. The Mobile Node/Router should
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de-register its binding from the old Home Agent before the home
registration to the new Home Agent.
The scenarios for the HAHA protocol are described in Section 8. In
the solo Home Agent activation scenario, only a primary Home Agent
manages a binding for a Mobile Node/Router and takes responsibility
for tunneling packets from and to a Mobile Node/Router. The Mobile
Node/Router can switch its primary Home Agent to a Home Agent located
in different link by the HAHA protocol.
In the Multiple Home Agents activation scenario, a primary Home
Agent shares the registered binding for a Mobile Node/Router with
all other Home Agents. Each Home Agent intercepts packets and take
responsibility for delivering intercepted packets to either the
Mobile Node/Router or the primary Home Agent. The Mobile Node/Router
accepts tunneled packets directly from the Home Agent. Otherwise,
when the primary Home Agent receives tunneled packets from other Home
Agents, it delivers packets to the Mobile Node/Router. The Mobile
Node/Router always tunnels outgoing packets to the primary Home
Agent. The Mobile Node/Router can switch its primary Home Agent to a
Home Agent located in different link by the HAHA protocol.
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4. Message Formats
4.1. New ICMP Messages
4.1.1. Home Agent Solicitation Message
The Home Agents Solicitation message is only used if a particular
entry is expiring in the Home Agents list and there has been no
unsolicited Home Agent Advertisement message from the Home Agent
whose entry is expiring.
The Home Agent Solicitation message has similar format of Route
Solicitation message [8]. The Home Agent Solicitation message
MUST be unicasted to invoke Home Agent Advertisement messages to
other Home Agents. The Home Agent Solicitation message MUST NOT be
multicasted and MUST NOT be used for Home Agents located at the local
link.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
The Source Address filed of the IPv6 header MUST be set to a
originator (Home Agent) address. The Destination Address field of
the IPv6 header MUST be set to an IPv6 global unicast address of
other Home Agents. Both a non-global scope address and non unicast
address MUST NOT be used in a Home Agent Solicitation message. The
Hop Limit field of the IPv6 header MUST be set to an initial hop
limit value, similarly to any other unicast packet.
The fields of a Home Agent Solicitation message are same as a Router
Solicitation message except for the Type field. The type field MUST
be set to 155 (To Be Assigned by IANA).
Home Agent Solicitation message MUST be authenticated and encrypted
by the use of IPsec ESP.
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4.1.2. Home Agent Advertisement Message
The Home Agent Advertisement messages are sent between Home Agents to
maintain the Home Agents List at each Home Agent.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H| Reserved| Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
The Source Address filed of the IPv6 header MUST be set to a
originator (Home Agent) address. The Destination Address field of
the IPv6 header MUST be set to the global unicast address of another
Home Agent. Non-global scope or non-unicast addresses MUST NOT be
used in a Home Agent Advertisement message. The Hop Limit field of
the IPv6 header MUST be set to an initial hop limit value, similarly
to any other unicast packet.
The fields of a Home Agent Advertisement message are same as a Router
Advertisement message except for the Type field. The type field MUST
be set to 156 (To Be Assigned by IANA).
A Prefix Information Option and a Home Agent Information Option MUST
be included in a Home Agent Advertisement message. The treatment of
options is same as options defined in Mobile IPv6 [1].
Home Agent Advertisement message MUST be authenticated and encrypted
by IPsec ESP.
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4.2. New Mobility Header Messages
The Mobility Header format is defined in section 6 of [1]. This
document defines three new mobility messages for Binding Cache
information exchange and for switching primary Home Agents.
4.2.1. Binding Information Request Message
The Binding Information Request Message is used to request Binding
Cache Information corresponding to a particular Mobile Node/Router.
It is sent only between Home Agents. The format of the 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility Options .
. .
. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Identifier
The 16-bit identifier to aid in matching Home Agent Information
Reply message. The identifier should never be set to 0. It
should always be more than 1.
This message MUST include either the Home Address mobility option
4.3.1 or the Mobile Network Prefix Option 4.3.2. If a Home
Agents want the Binding Cache Information for a particular Mobile
Node/Router it includes a Home Address mobility option. If a Home
Agent wants to know the forwarding state setting up for a particular
Mobile Network Prefix, it includes the Mobile Network Prefix Option.
This message is optional if Home Agents send out unsolicited Binding
Information Reply messages.
Binding Information Request message MUST be authenticated and
encrypted by IPsec ESP.
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4.2.2. Binding Information Reply Message
The Binding Information Reply message is used by the Home Agents
to exchange Binding Cache Information. The message 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility Options .
. .
. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Identifier
The identifier should be set 0 for unsolicited Binding
Information Reply messages. Otherwise, the identifier should
be set to the identifier in a Binding Information Request
message if this is a solicited Binding Information Reply
message.
Binding Information Reply message MUST be authenticated and encrypted
by IPsec ESP.
4.2.3. Home Agent Switch Request Message
This message is sent by a Home Agent to a Mobile Node/Router to
trigger Dynamic Home Agent Discovery. The message 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Agent Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Reserved
16-bit field reserved for future use. The value SHOULD be
initialized to zero by the sender, and MUST be ignored by the
receiver.
Home Agent Address
A 16 byte field contains the new primary Home Agent Address.
The Home Agent address MUST be recorded in the Home Agent list
of the Mobile Router. If this field does not contain the
valid global IPv6 address or the unknown Home Agent address,
the Mobile Router sends dynamic Home Agent address discovery
request message. Otherwise, the Mobile Router switches to this
Home Agent immediately as its primary Home Agent.
Home Agent Switch Request message MUST be authenticated and encrypted
by the use of IPsec ESP mode.
4.3. New Mobility Options
4.3.1. Home Address
The Home Address option has an alignment requirement of 8n+6. 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 = 0x8 | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Home Address |
+ +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This option is used when the Home Agent needs to figure out the
Binding Cache information for a particular Mobile Node or Mobile
Router. not useful when each Home Agent sends an unsolicited binding
cache information for each BU it receives.
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4.3.2. Mobile Network Prefix Option
This option is already defined in the Nemo basic support [6]. This
option is included in the Binding Information Request message only if
a Home Agent is requesting information regarding a particular Mobile
Network Prefix.
4.3.3. Binding Cache Entry Information Option
The Binding Cache Entry Information option has an alignment
requirement of 8n+2. 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 = 0x9 | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Home Address |
+ +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Care-of Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime | Number of MNPs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Mobile Network Prefixes .
. .
Binding Cache Entry Information option is valid in the Binding
Information Reply.
The fields of Home Address, Care-of Address, Flags, Sequence Number,
and Lifetime are copied from the registered binding of a particular
Mobile Node or Mobile Router.
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The field ``Number of MNPs'' tells the receiving Home Agent which
Mobile Network Prefixes are owned by a Mobile Router. The receiving
Home Agent can then setup forwarding for each Mobile Network Prefix.
for Mobile IPv6, the ``Number of MNPs'' field is set to 0.
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5. Home Agent Lists Management
Mobile IPv6 uses Router Advertisement messages to manage Home Agent
lists on each Home Agents. When home agents are placed at different
links, Router Solicitation and Advertisement messages can not be
used due to link-local limitation. Therefore, we defined new ICMP
messages to exchange similar information of Router Solicitation and
Advertisement among Home Agents over the home link.
A Home Agent MUST know other Home Agents which configured in
different links beforehand. This is manually configured on each
Home Agent. This mechanism MUST be used only between Home Agents on
different links serving the same home prefix. It SHOULD not be used
between Home Agents on the same link.
If a Home Agent Solicitation message or a Home Agent Advertisement
message is received from unknown Home Agent, the message MUST be
silently dropped.
5.1. Requesting Home Agent Information
A Home Agent sends a Home Agent Solicitation message when the home
agent wants to update information of a particular Home Agent. This
is useful a Home Agent boots up and starts acting as a home agent or
when the lifetime of a Home Agent list entry is about to expire.
A sender Home Agent MUST construct the Home Agent Solicitation in the
same manner as a Router Solicitation message [8] and MUST unicast it
to the target Home Agent.
The receiver MUST verify the Source address field of the IPv6 header.
If the source address is not among the known Home Agents, the
message MUST be discarded. If the Home Agent Solicitation message is
processed successfully, the receiver sends a Home Agent Advertisement
message to the Home Agent which solicits the information.
5.2. Notifying Home Agent Information
A Home Agent MUST send a Home Agent advertisement message when
it receives a valid Home Agent Solicitation message. The Home
Agent SHOULD also send a Home Agent Advertisement when its local
information such as preference, lifetime, and registration status,
etc. changes.
A Home Agent Advertisement MUST be constructed as same manner as a
Router Advertisement message described in section 7 of [1] and MUST
be sent by a unicast to the destination (other Home Agents).
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The receiver of a Home Agent Advertisement MUST verify the Source
address field of the IPv6 header. If the source address is not in
the list of know Home Agents, the message MUST be silently dropped.
Otherwise, the receiver processes the Home Agent Advertisement
message to update its Home Agent list.
The receiver MUST NOT treat the Home Agent Advertisement as a Router
Advertisement for the address autoconfiguration or the default
router list management. The Home Agent Advertisement MUST be used
only for the Home Agent list management. Therefore, the Home Agent
Advertisement MUST have Home Agent (H) bit and MUST have a Modified
Prefix Information Option and a Home Agent Information Option. If
these are not included in the Home Agent Advertisement message, the
receiver MUST ignore the message.
Any Home Agent Advertisement message satisfying all of these tests
MUST be processed to update its Home Agent list according to the
processing rules described in section 10.5.1 of [1].
6. Binding Synchronization among Home Agents
A binding for a particular Mobile Node/Router is shared among Home
Agents. Therefore, each Home Agents can always know the binding
for a particular Mobile Router and the primary Home Agent which is
currently serving the Mobile Router. This makes it possible for
Mobile Routers to utilize multiple Home Agents simultaneously.
6.1. Requesting Binding
When a Home Agent wants a binding for a particular Mobile
Node/Router, it can solicit Binding Information Reply message. The
Home Agent sends a Binding Information Request message to the primary
home agent of the Mobile Node/Router. The Home Agent MUST set a
random value to the Identifier field in the Binding Information
Request message and MUST include either a Home Address mobility
option or a Mobile Network Prefix mobility option.
6.2. Notifying Binding
The primary Home Agent sends Binding Information Reply messages when
it is solicited by Binding Information Request message or when it
creates or updates binding for a particular Mobile Node/Router.
When the primary Home Agent receives a Binding Information Request
message, it MUST verifies the Source address field of the IPv6
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header. If the source address is not among the know Home Agents, the
message MUST be silently discarded.
If a Home Agent who receives a Binding Information Request message is
not the primary Home Agent for the requested Mobile Node/Router, it
MUST ignore the message. Otherwise, it SHOULD reply to the Binding
Information Request message.
The binding information of the requested Mobile Node/Router are
stored in the Binding Information Reply message. The primary Home
Agent MUST copy the binding information of the requested Mobile
Node/Router to each fields of a Binding Cache Entry Information
option. If the Binding Information Reply message is sent in response
to the Binding Information Request message, the primary Home Agent
MUST copy the Identifier field of the Request message to the same
filed in the Reply message. Otherwise, it MUST set zero to the
Identifier field.
When a Home Agent receives a Binding Information Reply message, it
MUST verify the Source address field of the IPv6 header. If the
source address is not among the know Home Agents, the message MUST be
silently discarded. If the Binding Information Reply message is sent
from the primary Home Agent, the Home Agent SHOULD record the binding
information and the primary Home Agent address into its Binding
Cache.
Both a Binding Information Reply message and a Binding Information
Request message MUST be authenticated and encrypted by IPsec ESP.
If a message does not have IPsec ESP header, the message MUST be
ignored.
7. Primary Home Agent Switching
A Mobile Router always associates with the best Home Agent from home
agents configured for the Mobile Router. The Mobile Router initiates
dynamic Home Agent discovery to get the most appropriate home agents.
The Mobile Router can ensure the best Home Agent by issuing a dynamic
Home Agent address discovery request message at each visiting foreign
links. Alternatively, Home Agent can send Home Agent Switch Request
message as a trigger of a dynamic Home Agent address discovery
request message to the Mobile Router.
The Home Agent initiated switching is useful for load-sharing of each
Home Agents. A Home Agent can control the load average by moving
some of Mobile Routers to other Home Agents compulsory.
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The Mobile Router initiated switching guarantees a Mobile Router
to register its binding to the best Home Agent all the time. For
example, the best Home Agent is the nearest one.
7.1. Home Agent initiated Switching
A Mobile Router can change its primary Home Agent when it is
requested by a Home Agent. When a Mobile Router receives a Home
Agent Switch Request, it checks the Home Address field in the
request. If the address in the Home Address field is global scope
address and is already recorded in the Home Agent list of the Mobile
Router, the Mobile Router immediately switches to the requested
Home Agent by the Home Agent Switch Request. On the other hand,
the Mobile Router MUST send a Dynamic Home Agent Discovery Request
message to the Mobile IPv6 Home-Agents anycast address. After
receiving a Dynamic Home Agent Discovery Reply, the Mobile Router
selects the most appropriate home agent and changes its primary Home
Agent to the selected Home Agent.
The primary Home Agent switching is completed when the Mobile Router
registers its binding to the new Home Agent.
7.2. Mobile Router initiated Switching
When a Mobile Router decides to change its primary Home Agent, it
selects the new Home Agent from its Home Agent list. The Mobile
Router can start Dynamic Home Agent Address Discovery to update Home
Agents information such as a preference value of each Home Agents.
After selection of a new Home Agent, it registers its binding to the
new Home Agent.
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8. Scenarios
8.1. Solo Home Agent Activation
MR PHA HA2 HA3 CN
| | | | |
|------>| | | | 1. Home Registration
| | | | |
|======>|---------------------->| 2. Sending Packet to CN
| | | | | via Primary HA"(PHA)
|<======|<----------------------| 3. Sending Packet to MN/MR
| | | | | via PHA
|<------|(HA1) | | | 4. Trigger primary HA switching
| | | | |
|-------------->|(PHA) | | 5. Sending Binding Update
| | | | |
| |<------|------>| | 6. Soliciting the binding
| | | | | to other HAs. (no reply)
|<--------------| | | 7. Sending Binding Acknowledgement
| | | | |
|==============>|-------------->| 8. Sending Packet to CN
| | | | |
|<==============|<--------------| 9. Sending Packet to CN
| | | | |
Figure 1: Solo Home Agent with single bi-directional tunnel
This scenario is only valid for the Nemo basic support. Only the
primary Home Agent advertises a home prefix and mobile network
prefixes (might be aggregated in terms of extended/aggregated home
prefix [7]) to the Internet in Fig 1. When a Home Agent receives a
Binding Update from a Mobile Router and processes the Binding Update
successfully, it enables route distribution for the mobile network
prefixes. On the other hand, if the Home Agent receives a Binding
Update requesting to delete the binding (de-registration), it stops
distributing routes for the mobile network prefixes. The Home Agent
should not stop route distribution when the binding is expired due to
lifetime expiration. The Home Agent needs explicit de-registration
(i.e. Binding Updates for de-registration) to stop the routes
distribution.
All packets meant for the mobile network are routed to the primary
Home Agent and are intercepted by the primary Home Agent as well as
the Nemo basic support. Then, the primary Home Agent tunnels packets
to the Mobile Router according to the forwarding states established
by a Binding Update (Seq2 and Seq3).
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When the Mobile Router switches its primary Home Agent, it sends a
Binding Update to the new primary Home Agent (Seq5). The new primary
Home Agent receiving the Binding Update verifies whether the other
Home Agents still hold the binding for the Mobile Router. It sends
Binding Information Request messages to all the other Home Agents
(Seq6). If it receives any Binding Information Reply message in
response to the Binding Information Request messages, it sends a
Binding Acknowledge to the Mobile Router with the status value set to
144 (another Home Agent is still active). Otherwise, the Home Agent
accepts the Binding Update and becomes the primary Home Agent for the
Mobile Router (Seq7).
If the Mobile Router receives the Binding Acknowledge with a negative
status code, it de-registers its binding from the old primary home
agent and retries to send a Binding Update to the new primary home
agent. Before trying home registration to the new Home Agent, the
Mobile Router should de-register its binding from the current primary
Home Agent.
When the Mobile Router receives a Home Agent Switch Request from the
current primary Home Agent, it MUST switch its primary Home Agent
to the new Home Agent specified in the Home Agent Switch Request.
The Mobile Router can also switch the primary Home Agent proactively
without the Home Agent Switch Request.
8.2. Multiple Home Agent Activation
This scenario can be applied to both Mobile IPv6 and the Nemo basic
support protocol. Each Home Agent advertises the same home prefix
to the Internet. In the Nemo case, all the Home Agents having a
binding for a Mobile Router MUST distribute routes for mobile network
prefixes as well as the home prefix. The home prefix and the mobile
network prefixes could be aggregated in terms of extended/aggregated
home prefix described in [7].
Each Home Agent synchronizes a binding for a particular Mobile
Node/Router by the HAHA protocol. If all the Home Agents who have
the binding for the Mobile Router can setup forwarding for the Home
Address and the mobile network prefixes owned by the Mobile Router,
it tunnels intercepted packets directly to the Mobile Node/Router
(Fig 3). On the other hand, if the Home Agent does not enable
forwarding for the Home Address and the mobile network prefixes,
it tunnels intercepted packets to the primary Home Agent (Fig 2)
first. Then the primary Home Agent re-tunnels packets to the Mobile
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MN/MR PHA HA2 CN1 HA3 CN2
| | | | | |
|------>| | | | | 1. Home Registration
| | | | | |
| |------>| | | | 2. Sending binding to HA2
| | | | | |
| |---------------------->| | 3. Sending binding to HA3
| | | | | |
|======>|-------------->| | | 4. Sending Packet to CN1
| | | | | | via PHA
|<======|<------|<------| | | 5. Sending Packet to MN/MR
| | | | | | via HA2 and PHA
|======>|------------------------------>| 6. Sending Packet to CN2
| | | | | | via PHA
|<======|<----------------------|<------| 7. Sending Packet to MN/MR
| | | | | | via HA3 and PHA
|-------------->|(PHA) | | | 8. Home Registration
| | | | | |
| (HA1)|<------|-------------->| | 9. Sending binding to
| | | | | | HA1 and HA3
|==============>|---------------------->| 10. Sending Packet to CN2
| | | | | | via PHA
|<==============|<--------------|<------| 11. Sending Packet to MN/MR
| | | | | | via HA3 and PHA
Figure 2: Multiple Home Agents with single bi-directional tunnel
Node/Router. It is a matter of operations whether forwarding setting
is enable on all the Home Agent or not.
In the figure 2, a Mobile Node/Router first registers its binding to
the primary Home Agent (Seq1). Once the primary Home Agent creates
a binding for the home address of the Mobile Node/Router and sets
up forwarding for the mobile network prefixes, it sends Binding
Information Reply messages to other Home Agents to synchronize the
binding information (Seq2 and Seq3). When a Home Agent receives the
Binding Information Reply message, it records the binding and the
primary Home Agent address (which can be retrieved from the source
address of the Binding Information Reply messages) in the binding
cache entry.
After the completion of the binding synchronization, all Home
Agents start to distribute the network routes for the mobile network
prefixes to the Internet. Therefore, when the mobile network node
communicates with a correspondent node, outgoing packets from the
mobile network are tunneled to the closer primary Home Agent (Seq4)
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and incoming packets to the mobile network are intercepted by the
Home Agent which is close to the correspondent node (Seq5). Then,
the intercepted packets are forwarded/tunneled to the primary Home
Agent. The primary Home Agent delivers the packets to the Mobile
Router through the bi-directional tunnel (Seq5).
If the Mobile Router decides to switch its primary Home Agent due
to its movement, it sends a Binding Update to the new primary home
agent. Then, the new primary Home Agent starts to synchronize the
binding information with other Home Agents (Seq9). All Home Agent
updates the binding and the primary Home Agent address according to
the received Binding Information Reply message.
MN/MR HA1 HA2 CN1 HA3 CN2
| | | | | |
|------>| | | | | 1. Home Registration
| | | | | |
| |------>| | | | 2. Sending the binding
| | | | | | to HA2
| |---------------------->| | 3. Sending the binding
| | | | | | to HA3
|======>|-------------->| | | 4. Sending Packet to CN1
| | | | | | via HA1
|<==============|<------| | | 5. Replying to MN/MR
| | | | | | via HA2
|======>|------------------------------>| 6. Sending Packet to CN2
| | | | | | via HA1
|<==============================|<------| 7. Replying to MN/MR
| | | | | | via HA3
Figure 3: Multiple Home Agents with multiple
bi-directional tunnels
In the figure 3, a Mobile Node/Router first sends a Binding Update
to its primary Home Agent (Seq1). The primary Home Agent also
notifies the binding information to other Home Agents by using
Binding Information Reply messages (Seq2 and Seq3). When a Home
Agent receives the Binding Information Reply message, it records the
binding and the primary home agent address as a binding cache entry
for the Mobile Node/Router and sets up forwarding for mobile network
prefixes if any.
After creating the binding cache entry and setting up forwarding,
each Home Agent starts to distribute network routes for the mobile
network prefixes to the Internet. When the Mobile Network Node
communicates with a Correspondent Node, outgoing packets from
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the mobile network are tunneled to the primary Home Agent (Seq4).
Incoming packets to the mobile network are intercepted by the Home
Agent which is close to the Correspondent Node (Seq5). Then, the
intercepted packets are tunneled directly to the current Care-of
Address according to binding and forwarding (Seq5).
The procedure of primary Home Agent switching is same as the
procedure described in Fig 2.
9. Modifications to Mobile IPv6 and the Nemo Basic Support Protocol
The HAHA protocol modifies the below items of Mobile IPv6 [1] and the
Nemo Basic Support protocol [6].
- The new status values for the Binding Acknowledgment.
When a Mobile Node/Router receives this status for its home
registration, it MUST de-register its binding from the old
primary Home Agent and SHOULD re-try home registration. A
Home Agent SHOULD use this status value only in the solo Home
Agent activation scenario. The primary Home Agent can not be
duplicated in the scenario and can only have a binding for a
particular Mobile Node/Router all the time.
Status
144 Another primary Home Agent is still active.
- Binding Cache Registration
The conceptual fields of each Binding Cache entry are defined
in [1]. The HAHA protocol introduces an additional field to
record the primary Home Agent address for a Mobile Node/Router.
When a Home Agent receives a Binding Information Reply message,
it creates or updates the binding cache entry. The Home Agent
MUST record the primary Home Agent address in the binding cache
entry. The address can be derived from the Source address field
of IPv6 header in the Binding Information Reply message.
When a primary Home Agent receives a Binding Update from a Mobile
Node/Router, it MUST records its own address as the primary Home
Agent address in the binding cache entry.
- Tunneling packets to Mobile Node/Router from Home Agents
Home Agents who registers a binding by the HAHA protocol can
tunnel packets meant for the Mobile Node/Network to the current
Care-of Address as well as the primary Home Agent. The Mobile
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Node/Router can accept the tunneled packets. The Mobile
Node/Router MUST know all the Home Agents who has its binding in
the home agent list so as to verify the Source address of outer
IPv6 header.
- Tunneling packets to primary Home Agent from Home Agents
When one of Home Agents who has a binding intercepts packets
meant for a particular Mobile Node/Router, the Home Agent can
tunnel packets to the primary Home Agent recorded in the binding
cache. The primary Home Agent tunnels packets to the current
Care-of Address of the Mobile Node/Router.
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10. IANA Considerations
This document defines two new ICMP options
- Home Agent Solicitation Message
- Home Agent Advertisement Message
This document defines three new Mobility Header messages
- Binding Information Request Message
- Binding Information Reply Message
- Home Agent Switch Request Message
This document defines two new Mobility Options.
- Home Address
- Binding Cache Entry Information
11. Security Considerations
Multiple Home Agents advertise routes for either same Home Prefix and
possibly Mobile Network Prefix in the HAHA protocol, these routes
MUST be correctly advertised. System Administrators MUST prevent
malicious (blackhole) routes for these prefixes.
A Home Agent MUST know the other Home Agent serving a same Mobile
Node/Router and MUST establish a secure association with each Home
Agent. All signaling messages between the Mobile Router and the Home
Agent MUST be authenticated and encrypted by IPsec ESP [4].
The Mobile Node/Router MUST verify that packets are tunneled through
the known Home Agent. In Multiple Home Agent activation scenario,
the Mobile Node/Router may receives packets tunneled by multiple Home
Agents. The Mobile Node/Router MUST know all Home Agents who has its
binding by the HAHA protocol in its Home Agent List by using Home
Agent Address Discovery. It is necessary for a Mobile Node/Router to
know all other Home Agents in order to protect attacks launched by
malicious Home Agents.
Please refer to the Mobile IPv6 specification [1] and the Nemo Basic
Support protocol specification [6] for security considerations.
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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. 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] S. Kent and R. Atkinson. IP Encapsulating Security Payload (ESP).
RFC 2402, IETF. November 1998.
[5] A. Conta and S. Deering. Generic Packet Tunneling in IPv6
Specification. RFC 2473, IETF. December 1998.
[6] V. Devarapalli and R. Wakikawa and A. Petrescu and P. Thubert.
Nemo Basic Support Protocol (work in progress). Internet Draft,
IETF. draft-ietf-nemo-basic-support-01.txt September 2003
[7] P. Thubert and R. Wakikawa and V. Devarapalli. Examples of
basic Nemo usage (work in progress). Internet Draft, IETF.
draft-ietf-nemo-basic-usage-00.txt October 14 2003.
[8] T. Narten and E. Nordmark and W. Simpson. Neighbor Discovery for
IP Version 6 (IPv6). RFC 2461, IETF. December 1998.
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A. Predictive HA discovery
There are at least 3 approaches in order to locate the Home Agent
that has a registration for a given Mobile Node, Router or Mobile
Network:
- reactive: This method is also referred to as 'on-demand'. In
case of a binding cache miss, a Home Agent floods a request to
all the other Home Agents with the (destination of the packet)
home address that is sought for. Every Home Agent that has
a registration for that home address or for a Mobile Network
that encompasses that home address responds. This approach is
traditionally used in fast changing configurations, for instance
if Mobile Nodes register and de-register very often.
- proactive: an information is pushed to all Home Agents with
the home address and the Mobile Network Prefixes each time a
primary binding entry is created for a new registration. This
approach is preferred for stable configurations, for instance if
Mobile IP is used as a tool to simplify the configuration and
reconfiguration of mostly stable networks.
- predictive: Ranges of Home Addresses and prefixes are assigned
to the Home Agents, following a rule that is commonly computed by
all Home Agents. Dynamic Home Agent Address Discovery (DHAAD)
returns only the address of one Home Agent, the one that is
pre-allocated for that Mobile Node. When the wrong Home Agent
intercepts packets, it can compute which is the right Home Agent
and forward packets to it at L2 if they are directly connected,
or via a HAHA tunnel which is established between Home Agents.
This is what we call 'Z' routing.
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CN --------> closest HA CN ----------> closest HA
/ |
/ |
/ |
/ |
/ |
Assigned / |
HA v V
----------> Mobile Node Mobile Node
Figure 4: Z routing vs dogleg
The Predictive Mode minimizes the control traffic, which may be
required for a large configuration. Some additional controls would
be necessary for the HAHA protocol to allow the negotiation and the
distribution of the shares of Home to be attributed to each Home
Agent.
One specific advantage of not relying on a Home Link for HAHA
communication is that for a large configuration, the Home Agents can
be organized hierarchically and distributed geographically, as a set
of local clusters linked together to form a global Home Network.
For instance, it is possible for a large ISP to partition the Home
Network for a given worldwide service, and assign a partition to a
cluster of Home Agents in each of the geographies. In predictive
mode, each Home Agent in the world would be able to compute the
best suited Home Agent in its local cluster (call this a Acting
Home Agent) and the best suited Home Agent worldwide (call this the
Assigned Home Agent) for each and any Home Address.
Any Home Agent processing a anycast DHAAD can predict the Assigned HA
and local Acting Home Agents for a Home Address if that information
is added to the DHAAD request. In the case of Mobile Routers, the
service must be arranged in such ways that, for a given registration,
all the Mobile Networks are assigned to a same Home Agent.
Possible flows:
In order to register, a Mobile Router uses DHAAD which returns one
Home Agent in the closest cluster. This can be a Acting HA if the
Mobile Node is roaming far from Home, but hopefully it is in general
the Assigned Home Agent for that Mobile Node. When this is a Acting
HA, it needs to register to the Assigned HA as proxy binding.
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+----------------------------------
| +-------------+ ^ ^
| | +-----+ | ^ | |
| | | MNP | | | | |
| | +-----+ | HA | | cluster |
| | +-----+ | share | | share |
| | | MNP | | | | |
| | +-----+ | v | |
| | +-----+ | ^ | |
| | | | | | | |
| | +-----+ | HA | | |
| | +-----+ | share | | |
| | | | | | | |
| | +-----+ | v | |
| | | | |
| | Local Home | | |
| | Network | v |
| +-------------+ |
| |
| +-------------+ |
| | | |
| | +-----+ | |
| | | | | global |
| | +-----+ | Home |
| | | Network |
| +-------------+ |
+--------------------------------- v
Figure 5: Distributed Hierarchical Home Network
When a packet destined to a given Home Address arrives at a Home
Agent from a Correspondent Node:
If the Home Agent is Assigned for that Home Address and it has a
direct registration (it is primary), the Home Agent forwards the
packet over its bi-directional tunnel established with the Mobile
Node/Router (the MRHA tunnel). If it has a proxy registration (it
is secondary), it forwards the packet to the primary Acting HA - or
directly to the Mobile Node/Router if that is practical for tunnel
setup and security reasons. Else it drops the packet.
Else If the Home Agent is Acting HA for that Home Address and it has
a direct registration (it is primary), the Home Agent forwards the
packet over its MRHA tunnel. If it has a proxy registration (it is
secondary), it forwards the packet to the primary Acting HA - or
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directly to the Mobile Node if that is practical for tunnel setup and
security reasons. Else, it forwards the packet to the Assigned HA.
CN ----------> Acting HA
/ closest to CN
/
/
/
Assigned /
HA V
"
"
"
"
"
" Acting HA primary
MN <----------- for that registration
(closest to MR)
Figure 6: Acting HA to Acting HA without Route Optimization
CN ----------> closest HA
| to CN
|
|
|
|
v Acting HA, primary
MN <--------- for that registration
(closest to MR)
Figure 7: Acting HA to Acting HA Route Optimization
Else (if the HA is the 'wrong Home Agent') the Home Agent tunnels
the packet to the best suited of the local Home Agents, be it the
Assigned Home Agent, or a local Acting Home Agent.
In the worst case, the packet may bounce from the receiving Home
Agent to the local Acting HA, then to the Assigned HA, and finally to
the Acting HA that has the registration. It is up to the Assigned
Home Agent to forward the proxy binding states to the Acting Home
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Agent on the receiving side in order to allow Acting HA to Acting HA
'Z' routing.
If the Home Agents are distributed geographically, it is expected
that, in general, the angles of the Z (the Home Agents) are close to
the Mobile Router and Correspondent Node respectively, relatively to
the distance between the Home Agents, which makes the cost of the
bouncing acceptable in terms of distance and hops.
When a packet from a registered Mobile Node arrives over the MRHA
tunnel to a Home Agent (one that it is registered to), the Home Agent
forwards the packet directly to the Correspondent Node. That Home
Agent is supposed to be close to the Mobile Node, making the MR-HA-CN
triangle as flat as possible and limiting the cost of the dogleg.
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Authors Addresses
Ryuji Wakikawa
Keio University and WIDE
5322 Endo Fujisawa Kanagawa
252-8520
Japan
Email: ryuji@sfc.wide.ad.jp
Vijay Devarapalli
Nokia Research Center
313 Fairchild Drive
Mountain View, CA 94043
USA
Email: vijay.devarapalli@nokia.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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