One document matched: draft-ietf-mobileip-hmipv6-07.txt
Differences from draft-ietf-mobileip-hmipv6-06.txt
IETF Mobile IP Working Group Hesham Soliman, Ericsson
INTERNET-DRAFT Claude Castelluccia, INRIA
Karim El-Malki, Ericsson
Ludovic Bellier, INRIA
October, 2002
Hierarchical Mobile IPv6 mobility management (HMIPv6)
<draft-ietf-mobileip-hmipv6-07.txt>
Status of this memo
This document is a submission by the mobile-ip Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the MOBILE-IP@SUNROOF.ENG.SUN.COM mailing list.
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
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documents at any time. It is inappropriate to use Internet-Drafts
as reference material or cite them other than as "work in
progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/lid-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
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Abstract
This draft introduces extensions to Mobile IPv6 and IPv6 Neighbour
Discovery to allow for local mobility handling. Hierarchical mobility
management for Mobile IPv6 reduces the amount of signalling between
the Mobile Node, its Correspondent Nodes and its Home Agent. The
Mobility Anchor Point described in this document can also be used to
improve the performance of Mobile IPv6 in terms of handoff speed.
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TABLE OF CONTENTS
1. Terminology............................................ 3
2. Introduction and motivation............................ 4
3. Overview of HMIPv6..................................... 5
4. Mobile IPv6 extension û local Binding Update........... 7
5. Neighbour Discovery extension û MAP option message .... 8
6. Protocol operations ................................... 10
6.1 Mobile Node Operation.............................. 10
6.2 MAP operation...................................... 12
6.3 Home Agent operation............................... 13
6.4 Correspondent Node operation....................... 13
6.5 Local Mobility Management optimisation
within a MAP domain................................ 13
6.6 Location Privacy................................... 13
7. MAP Discovery.......................................... 14
7.1 Dynamic MAP Discovery..............à.............. 14
7.2 Using Router Renumbering for MAP Discovery........ 15
7.3 MN Operation...................................... 17
8. Updating previous Anchor Points......................... 18
9. Special optimisations for sending Binding Updates....... 18
10. Notes on MAP selection by the MN........................ 18
11. Detection and recovery from MAP failures................ 20
12. Security considerations................................. 21
13. Acknowledgements........................................ 23
14. Notice Regarding Intellectual Property Rights........... 23
15. References.............................................. 24
16. Authors' addresses...................................... 25
17. Appendix A: Fast Mobile IPv6 handovers and HMIPv6....... 26
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1. Terminology
This memo uses the terminology described in [1]. In addition, new
terms are defined below:
Access Router (AR) The Mobile NodesÆ default router. The AR
aggregates the outbound traffic of mobile
nodes.
Mobility Anchor Point A Mobility Anchor Point is a router located
(MAP) in a network visited by the mobile node.
The MAP is used by the MN as a local HA.
One or more MAPs can exist within a visited
network.
Regional Care-of An RCoA is an address obtained by the
Address (RCoA) mobile node from the visited network. An
RCoA is an address on the MAPÆs subnet. It
is auto-configured by the mobile node when
receiving the MAP option.
HMIPv6-aware An HMIPv6-aware mobile node is a mobile
Mobile Node node that can receive and process the MAP
option received from its default router.
An HMIPv6-aware Mobile Node must also be
able to send a local binding updates
(Binding Update with the M flag set).
On-link CoA (LCoA) The LCoA is the on-link CoA configured on
an mobile nodeÆs interface based on the
prefix advertised by its default router.
In [1] this is simply referred to as the
Care-of-address. However, in this memo LCoA
is used to distinguish it from the RCoA.
Local Binding Update The MN sends a Local Binding Update to the
MAP in order to establish a binding
between the RCoA and LCoA.
Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and
"MAY" that appear in this document are to be interpreted as described
in [KEYWORDS].
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2. Introduction and motivation
This draft introduces the concept of a Hierarchical Mobile IPv6
network, utilising a new node called the Mobility Anchor Point (MAP).
Mobile IPv6 [1] allows nodes to move within the Internet topology
while maintaining reachability and on-going connections between
mobile and correspondent nodes. To do this a mobile node sends
Binding Updates (BUs) to its Home Agent (HA) and all Correspondent
Nodes (CNs) it communicates with, every time it moves. Authenticating
binding updates requires approximately 1.5 round trip times between
the mobile node and each correspondent node (for the entire return
routability procedure in a best case scenario, i.e. no packet
losses). In addition, one round trip time is needed to update the
Home Agent, this can be done simultaneously while updating
correspondent nodes. The re-use of the home cookie (i.e. eliminating
HOTI/HOT) will not reduce the number of round trip times needed to
update correspondent nodes. These round trip delays will disrupt
active connections every time a handoff to a new AR is performed.
Eliminating this additional delay element from the time-critical
handover period will significantly improve the performance of Mobile
IPv6. Moreover, in the case of wireless links, such solution reduces
the number of messages sent over the air interface to all
correspondent nodes and the Home Agent. A local anchor point will
also allow Mobile IPv6 to benefit from reduced mobility signalling
with external networks.
For these reasons a new Mobile IPv6 node, called the Mobility Anchor
Point is used and can be located at any level in a hierarchical
network of routers, including the Access Router (AR). Unlike Foreign
Agents in IPv4, a MAP is not required on each subnet. The MAP will
limit the amount of Mobile IPv6 signalling outside the local domain.
The introduction of the MAP provides a solution to the issues
outlined earlier in the following way:
- The mobile node sends Binding Updates to the local MAP rather than
the HA that is typically further away and CNs
- Only one Binding Update message needs to be transmitted by the MN
before traffic from the HA and all CNs is re-routed to its new
location. This is independent of the number of CNs that the MN is
communicating with.
A MAP is essentially a local Home Agent. The aim of introducing the
hierarchical mobility management model in Mobile IPv6 is to enhance
the performance of Mobile IPv6 while minimising the impact on Mobile
IPv6 or other IPv6 protocols. It also supports Fast Mobile IPv6
Handovers to help Mobile Nodes in achieving seamless mobility (see
Appendix A). Furthermore, HMIPv6 allows mobile nodes to hide their
location from correspondent nodes and Home Agents while using Mobile
IPv6 route optimisation.
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3. Overview of HMIPv6
This Hierarchical Mobile IPv6 scheme introduces a new function, the
Mobility Anchor Point(MAP), and minor extensions to the mobile node
operation. The correspondent node and Home Agent operation will not
be affected.
Just like Mobile IPv6, this solution is independent of the underlying
access technology, allowing mobility (including fast mobility [12])
within or between different types of access networks. Furthermore, a
smooth architectural migration can be achieved from Hierarchical
MIPv4 networks, since a dual operation of IPv4 and IPv6 Hierarchies
will be possible making use of the similarity in architecture.
A mobile node entering a MAP domain will receive Router
Advertisements containing information on one or more local MAPs. The
MN can bind its current location (on-link CoA) with an address on the
MAPÆs subnet (RCoA). Acting as a local HA, the MAP will receive all
packets on behalf of the mobile node it is serving and will
encapsulate and forward them directly to the mobile node's current
address. If the mobile node changes its current address within a
local MAP domain (LCoA), it only needs to register the new address
with the MAP. Hence, only the Regional CoA (RCoA) needs to be
registered with correspondent nodes and the HA. The RCoA does not
change as long as the MN moves within a MAP domain (see below for
definition). This makes the mobile node's mobility transparent to the
correspondent nodes it is communicating with.
A MAP domain's boundaries are defined by the Access Routers (ARs)
advertising the MAP information to the attached Mobile Nodes.
The detailed extensions to Mobile IPv6 and operations of the
different nodes will be explained later in this document.
It should be noted that the HMIPv6 concept is simply an extension to
the Mobile IPv6 protocol. An HMIPv6-aware mobile node with an
implementation of Mobile IPv6 SHOULD choose to use the MAP when
discovering such capability in a visited network. However, in some
cases the mobile node may prefer to simply use the standard Mobile
IPv6 implementation. For instance, the mobile node may be located in
a visited network within its home site. In this case, the HA is
located near the visited network and could be used instead of a MAP.
In this scenario, the mobile node would only update the HA whenever
it moves. The method to determine whether the HA is in the vicinity
of the MN (e.g. same site) is outside the scope of this document.
3.1 HMIPv6 Operation
The network architecture shown below illustrates an example of the
use of the MAP in a (visited) network.
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+-------+
| HA |
+-------+
|
| +----+
| | CN |
| +----+
+-----+ |
| |
| +---+
| |
+-------+
| MAP | RCoA
+-------+
| |
| +--------+
| |
| |
+-----+ +-----+
| AR1 | | AR2 |
+-----+ +-----+
+----+
| MN |
+----+ ------------>
Movement
Figure 1: Hierarchical Mobile IPv6 domain
In Figure 1, the MAP can help in providing seamless mobility for the
mobile node as it moves from Access Router 1 (AR1) to Access Router 2
(AR2), while communicating with the correspondent node. A multi-level
hierarchy is not required for a higher handover performance, hence,
it is sufficient to locate one or more MAPs (possibly covering the
same domain) at any position in the operatorÆs network.
Upon arrival in a visited network, the mobile node will discover the
global address of the MAP. This address is stored in the Access
Routers and communicated to the mobile node via Router Advertisements
(RAs). A new option for RAs is proposed later in this specification.
This is needed to inform mobile nodes about the presence of the MAP
(MAP discovery). The discovery phase will also inform the mobile node
of the distance of the MAP from the mobile node. For example, the MAP
function could be implemented as shown in Figure 1 and at the same
time also in AR1 and AR2. In this case the mobile node can choose the
first hop MAP or one further in the hierarchy of routers. The details
on how to choose a MAP are provided in section 10.
The process of MAP discovery continues as the mobile node moves from
one subnet to the next. As the mobile node roams within a MAP domain,
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ARs are configured to announce the same MAP address or addresses. If
a change in the advertised MAP's address is received, the mobile node
MUST act on the change by performing movement detection and sending
the necessary Binding Updates to its HA and correspondent nodes.
If the mobile node is not HMIPv6-aware then no MAP Discovery will be
performed, resulting in the mobile node using the Mobile IPv6 [1]
protocol for its mobility management. On the other hand, if the
mobile node is HMIPv6-aware it SHOULD choose to use its HMIPv6
implementation. If so, the mobile node will first need to register
with a MAP by sending it a BU containing its Home Address and on-link
address (LCoA). The Home address used in the BU is the RCoA. The MAP
MUST store this information in its Binding Cache to be able to
forward packets to their final destination when received from the
different correspondent nodes or HAs.
The mobile node will always need to know the original sender of any
received packets to determine if route optimisation is required. This
information will be available to the mobile node since the MAP does
not modify the contents of the original packet. Normal processing of
the received packets (as described in [1]) will give the mobile node
the necessary information.
To use the network bandwidth in a more efficient manner, a mobile
node may decide to register with more than one MAP simultaneously and
use each MAP address for a specific group of correspondent nodes. For
example, in Fig 1, if the correspondent node happens to exist on the
same link as the mobile node, it would be more efficient to use the
first hop MAP (in this case assume it is AR1) for communication
between them. This will avoid sending all packets via the "highest"
MAP in the hierarchy and hence result in a more efficient usage of
network bandwidth. The mobile node can also use its current on-link
address (LCoA) as a CoA as specified in [1].
If a router advertisement is used for MAP discovery, as described in
this document, all ARs belonging to the MAP domain MUST advertise the
MAP's IP address. A Router Renumbering [5] extension is also proposed
as an alternative for MAP discovery by ARs and MAPs. The same concept
(of advertising the MAPÆs presence within its domain) should be used
if other methods of MAP discovery are introduced in future.
4. Mobile IPv6 extension - Local Binding Update
This section outlines the extensions proposed to the BU used by the
mobile node in Mobile IPv6. A new flag is added: the M flag that
indicates MAP registration. When a mobile node registers with the
MAP, the M, D and A flags MUST be set to distinguish this
registration from a Home Registration or a BU being sent to a
correspondent node.
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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|S|D|L|M| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility Options .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Description of extensions to the binding update:
M If set indicates a MAP registration.
It should be noted that this Binding update uses the same Mobility
Header type specified in [1].
5. Neighbour Discovery extension - The MAP option message format
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 | Dist | Pref |R|I|P|V| Res |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Global IP Address for MAP +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type Message type. TBA.
Length 8-bit unsigned integer. The length of the
option (including the type and length fields)
in units of 8 octets. The value 0 is invalid.
Nodes MUST silently discard an ND packet that
contains an option with length zero.
Dist A 4 bit unsigned integer showing the distance
from the receiver of the advertisement. Its
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default value SHOULD be set to one if dynamic
MAP discovery is used. The Distance MUST be
set to one if the MAP is on the same link as
the mobile node. This field need not be
interpreted as the number of hops away from
the mobile node. The only requirement is that
the meaning of the Distance field is
consistently interpreted within one Domain. A
Distance value of Zero MUST NOT be used.
Pref The preference of a MAP. A 4 bit unsigned
integer. A decimal value of 15 indicates the
highest preference.
R When set indicates that the mobile node
MUST form an RCoA based on the prefix in the
MAP option.
I When set indicates that the mobile node MAY
use its RCoA as source address of its outgoing
packets
P When set indicates that the mobile node MUST
use its RCoA as source address of its outgoing
packets
V When set indicates that reverse tunnelling of
outbound traffic, to the MAP, is required if
RCoA is used as a source address in outgoing
packets.
Valid Lifetime The minimum value (in seconds) of both the
preferred and valid lifetimes of the prefix
assigned to the MAPÆs subnet. This value
indicates the validity of the MAPÆs address
and consequently the time for which the RCoA
is valid.
Global Address One of the MAP's global addresses.
The /64 prefix extracted from this address
MUST be configured in the MAP to be used for
RCoA construction by the mobile node.
Although not explicitly included in the MAP option, the prefix length
of the MAPÆs Global IP address MUST be 64. This prefix is the one
used by the mobile node to form an RCoA, by appending a 64-bit
identifier to the prefix. Hence the need for having a static prefix
length for the MAPÆs subnet.
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6. Protocol operation
This section describes the HMIPv6 protocol. In HMIPv6, the mobile
node has two addresses, an RCoA on the MAP's subnet and an on-link
CoA (LCoA). This RCoA is formed in a stateless manner by combining
the mobile nodeÆs interface identifier and the subnet prefix received
in the MAP option.
As illustrated in this section, this protocol requires special
treatment by the Mobile Nodes only. The HA is unchanged. The MAP
performs the function of a "local" HA that binds the mobile nodeÆs
RCoA to an LCoA.
6.1 Mobile node Operation
When a mobile node moves into a new MAP domain (i.e. its MAP
changes), it needs to configure two CoAs: an RCoA on the MAP's subnet
and an on-link CoA (LCoA). These addresses are formed in a stateless
manner. After forming the RCoA based on the prefix received in the
MAP option, the mobile node sends a local BU to the MAP with the A, M
and D flags set. The local BU is a BU defined in [1] which specifies
the MNÆs RCoA in the Home Address Option. No alternate-CoA option is
needed. The LCoA is used as the source address of the BU. This BU
will bind the mobile node's RCoA (similar to a Home Address) to its
LCoA. The MAP (acting as a HA) will then perform DAD for the mobile
node's RCoA on its link and return a Binding Acknowledgement to the
MN. This acknowledgement identifies the binding as successful or
contains the appropriate fault code. No new error codes need to be
supported by the MN for this operation. The MN MUST silently ignore
binding acknowledgements that do not contain a routing header type 2
which includes the mobile nodeÆs RCoA.
After registering with the MAP, the mobile node MUST register its new
RCoA with its HA by sending a BU that specifies the binding (RCoA,
Home Address) as in Mobile IPv6. The home address option is set to
the Home Address, the care-of address (RCoA) can be found in the
source address field or the alternate-CoA option. The MN may also
send a similar BU (i.e. that specifies the binding between the Home
Address and the RCoA) to its current correspondent nodes. If the I
flag is set in the MAP option, the mobile node MAY use its RCoA as a
source address for the BU. If the P flag is set in the MAP option,
the mobile node MUST use RCoA as a source address.
If the mobile node uses its RCoA as a source address, the alternate-
CoA option will not be required. If both the P and V flags are set,
the mobile node MUST use RCoA as a source address and tunnel all
outgoing packets to the MAP. The source address in the outer header
is the mobile nodeÆs LCoA and the destination address is the MAPÆs
address. This is done to allow for cases where a network
administrator wants mobile nodes to use RCoA as a source, while
keeping ingress filter configurations in the ARs unchanged.
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The mobile node SHOULD wait for the binding acknowledgement from the
MAP before registering with its HA. It should be noted that when
binding the RCoA with the HA and correspondent nodes, the binding
lifetime MUST NOT be larger than the mobile nodeÆs binding lifetime
with the MAP, received in the Binding Acknowledgement.
In order to speed up handoff between MAPs, a mobile node may send a
local BU to its previous MAP specifying its new LCoA. Packets in
transit that reach the previous MAP are then forwarded to the new
LCoA.
The MAP will receive packets addressed to the mobile node's RCoA
(from the HA or correspondent nodes). Packets will be tunnelled from
the MAP to the mobile node's LCoA. The mobile node will de-capsulate
the packets and process them in the normal manner.
When the mobile node moves locally (i.e. its MAP does not change), it
should only register its new LCoA with its MAP. In this case, the
RCoA stays unchanged.
Note that a mobile node may send a BU containing its LCoA (instead of
its RCoA) to correspondent nodes which are connected to its same
link. Packets will then be routed directly without going through the
MAP.
A network operator may prefer to hide the mobile nodeÆs LCoA from
nodes outside the MAP domain. To ensure this, a MAP option can be
sent with the P flag set. In this case, the mobile node MUST use its
RCoA as the source address of its BU (no alternate-CoA option is
needed) to its HA and correspondent nodes. It MUST also use its RCoA
as the source address for its outgoing packets.
On the other hand, a mobile node may prefer to hide its location from
the correspondent nodes it communicates with and the HA. To achieve
this, the mobile node should ensure that it does not provide both its
identity and location to any of the correspondent nodes. Since the
implied identity of the mobile node is included in every route-
optimised packet (a Home Address), the mobile node should ensure that
it does not provide its exact location to the correspondent nodes and
HA. Hence, the mobile node should use its RCoA as a source address
for all its outgoing packets. This can be done if the I or P flags
are set in the MAP option. Otherwise location privacy can not be
provided in this manner.
If the V flag is set (in addition to the P or I flags), the mobile
node MUST tunnel all outgoing packets to the MAP. This is needed to
allow for location privacy while keeping ingress filter configuration
in the ARs unchanged.
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6.1.1 Sending packets to correspondent nodes
The mobile node can communicate with a correspondent node through the
HA, or in a route-optimised manner, as described in [1}. When
communicating through the HA, the message formats in [1] can be re-
used. However, the mobile node MUST select the source address in
outgoing packets based on the content of the P, I and V flags in the
MAP option.
If the mobile node communicates directly with the correspondent node
(i.e. the CN has a binding cache entry for the mobile node), the
mobile node MUST use the same care-of address used to create a
binding cache entry in the correspondent node (RCoA) as a source
address. According to [1], the mobile node MUST also include a Home
Address option in outgoing packets. The Home address option must
contain the mobile nodeÆs home address.
Since RCoA is used as a source address for outgoing packets, the
mobile node must consider the content of the P, I and V flags to
decide whether packets should be sent directly with RCoA as a source,
or tunnel packets to the MAP. When tunnelling outgoing packets to the
MAP, the source address in the outer header is the mobile nodeÆs LCoA
and the destination address is the MAPÆs address.
6.2 MAP Operations
The MAP acts like a HA; it intercepts all packets addressed to
registered Mobile Nodes and tunnels them to the corresponding LCoA.
A MAP has no knowledge of the mobile node's Home address. The mobile
node will send a local BU to the MAP with the M, A and D flags set.
The aim of this BU is to inform the MAP that the mobile node has
formed an RCoA (contained in the BU as a Home address). If
successful, the MAP MUST return a binding acknowledgement to the
mobile node indicating a successful registration. Otherwise, the MAP
MUST return a binding acknowledgement with the appropriate fault
code. This is identical to the HA operation in [1]. If the operation
was successful, the MAP MUST respond with a binding acknowledgement
to the mobile node indicating a successful operation. Otherwise a
binding acknowledgement is sent with the appropriate error code. No
new error codes are introduced for HMIPv6. The binding
acknowledgement MUST include a routing header type 2 that contains
the mobile nodeÆs RCoA.
The MAP MUST be able to accept packets tunnelled from the mobile
node, with the mobile node being the tunnel entry point and the MAP
being the tunnel exit point. This is required independently of the
settings of the P, I, or V flags.
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The MAP then acts as a HA for the RCoA. Packets addressed to the RCOA
are intercepted by the MAP, using proxy Neighbour Advertisement,
encapsulated and routed to the mobile nodeÆs LCoA.
6.3 Home Agent Operations
The support of HMIPv6 is completely transparent to the HAÆs
operation. Packets addressed to a mobile nodeÆs Home Address will be
forwarded by the HA to its RCoA as described in [1].
6.4 Correspondent node Operations
HMIPv6 is completely transparent to correspondent nodes.
6.5 Local Mobility Management optimisation within a MAP domain
In [1], it is stated that for short-term communication, particularly
communication that may easily be retried upon failure, the mobile
node MAY choose to directly use one of its care-of addresses as the
source of the packet, thus not requiring the use of a Home Address
option in the packet. Such use of the CoA will reduce the overhead of
sending each packet due to the absence of additional options. In
addition, it will provide an optimal route between the mobile node
and correspondent node.
In HMIPv6, if the I or P flags are set in the MAP option, a mobile
node can use its RCoA as the source of its packets without using a
Home Address option. It may also use the RCoA as source address for
the local BU to register the binding between its LCoA and RCoA with
the local MAP. As a result the mobile node is seen by the
correspondent node as a fixed node while moving within a MAP domain.
This use of the RCoA can be useful as it does not have the cost
of Mobile IPv6 (i.e. no bindings or home address options are sent
over the Internet) but still provides some local mobility management
to the mobile nodes. Although, such use of RCoA does not provide
global mobility (i.e. communication is broken when a mobile host
moves to a new MAP), it would be useful for several applications
communicating with other nodes for some period of time depending on
the size of a MAP domain and the speed of the mobile node.
Furthermore, since the support for BU processing in correspondent
nodes is not mandated in [1], this mechanism can provide a way of
obtaining route optimisation without sending BUs to the correspondent
nodes.
6.6 Location Privacy
In HMIPv6, a mobile node MAY choose to hide its LCoA from its
corresponding nodes and its home agent by using its RCoA in the
source field of the packets that it sends. As a result, the location
tracking of a mobile node by its corresponding nodes or its home
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agent is difficult since they only know its RCoA and not its LCoA.
The MN may achieve such location privacy as described in section 6.1.
7. MAP discovery
This section describes how a mobile node obtains the MAP address and
subnet prefix and how ARs in a domain discover MAPs. Two different
methods for MAP discovery are defined below.
Dynamic MAP Discovery is based on propagating the MAP option in
Router Advertisements from the MAP to the mobile node through certain
(configured) router interfaces within the hierarchy of routers. This
would require manual configuration of the MAP and the routers
receiving the MAP option to allow them to propagate the option on
certain interfaces. To ensure a secure communication between routers,
router advertisements that are sent between routers for Dynamic MAP
discovery SHOULD be authenticated by AH or ESP. In the case where
this authentication is not possible (e.g. third party routers between
the MAP and ARs), a network operator may prefer to manually configure
all the ARs to send the MAP option or use the router renumbering
mechanism for MAP discovery, as shown in this document.
Another method based on Router Renumbering [5] is also described in
section 7.2. In this method, no manual configuration is required for
routers within the domain. The MAP option is sent directly from a
central node to all ARs within a MAP domain. This method is best
suited to large networks where manually configuring all routers
within a hierarchy can be a significantly tedious operation. On the
other hand, when using this method, any subsequent changes in the MAP
optionÆs parameters (e.g. preference) would require manual
intervention.
Manual configuration of the MAP option information in ARs and other
MAPs in the same domain is the default mechanism. It should also be
possible to configure ARs and MAPs to enable either dynamic or Router
Renumbering mechanisms for MAP Discovery.
7.1 Dynamic MAP Discovery
The process of MAP discovery can be performed in many different ways.
Router advertisements are used for dynamic MAP discovery by
introducing a new option. The access router is required to send the
MAP option in its router advertisements. This option includes the
distance vector from the mobile node which may not imply the real
distance in terms of the number of hops, the preference for this
particular MAP, the MAP's global IP address and the MAP's subnet
prefix. In addition, the option contains some flags showing the MAPÆs
mode of operation and other information.
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7.1.2 Router Operation for Dynamic MAP Discovery
The ARs within a MAP domain may be configured dynamically with the
information related to the MAP options. ARs may obtain this
information by listening for RAs with MAP options. Each MAP in the
network needs to be configured with a default preference, the right
interfaces to send this option on and the IP address to be sent. The
initial value of the "Distance" field MAY be set to a default value
of one. Routers in the MAP domain should be configured to re-send the
MAP option on certain interfaces
Upon reception of a router advertisement with the MAP option, the
receiving router MUST copy the option and re-send it after
incrementing the Distance field by one. If the receiving router was
also a MAP, it MUST send its own option together with the received
option in the same advertisement. If a router receives more than one
MAP option for the same MAP (i.e. the same IP address in the MAP
option), from two different interfaces, it MUST choose the option
with the smaller distance field.
In this manner, information about a MAP at a certain level in a
hierarchy can be dynamically passed to a mobile node. Furthermore, by
performing the discovery phase in this way, different MAP nodes are
able to change their preferences dynamically based on the local
policies, node overload or other load sharing protocols being used.
7.1.3 MAP Operation for Dynamic MAP Discovery
A MAP will be configured to send its option or relay MAP options
belonging to other MAPs onto certain interfaces. The choice of
interfaces is done by the network administrator (i.e. manual
configuration) and depends on the network topology. A default
preference value of 10 may be assigned to each MAP. It should be
noted that a MAP can change its preference value at any time due to
various reasons (e.g. node overload or load sharing). A preference
value of zero means that the MAP SHOULD NOT be chosen by new mobile
nodes. This value could be reached in cases of node overload or
partial node failures.
The MAP option is propagated down the hierarchy. Each router along
the path to the access router will increment the Distance field by
one. If a router that is also a MAP receives advertisements from
other MAPs, it MUST add its own MAP option and propagate both options
to the next level in the hierarchy.
7.2 Using Router Renumbering for MAP discovery
The Router Renumbering (RR) mechanism described in [2] defines a set
of messages that can be used to renumber certain interfaces on a
router without manual configuration of such router. RR messages are
authenticated and protected against replay attacks. The same concept
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can be used to configure a router to propagate the MAP option on
certain interfaces. A new PCO command, PROPAGATE, is defined below.
This command is part of the Prefix Code Operation (PCO) and is
included in the Match Prefix part of the message. A PCO message sent
to a router with the PROPAGATE command MUST contain one or more MAP
options in the Use Prefix part of the message.
Upon reception of this message, a router will propagate the MAP
option on the designated interface. This mechanism can be used to
configure ARs to advertise one or more MAP options. This is best
suited to large networks or for cases where third party networks may
exist between the MAP and ARs. Furthermore, unlike the Dynamic MAP
discovery mechanism described earlier, this method does not require
each router in the MAP domain to understand the MAP option.
7.2.1 Extension to the Match Prefix Part of RR
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OpCode | OpLength | Ordinal | MatchLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MinLen | MaxLen | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ MatchPrefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Extended Fields:
OpCode An unsigned 8-bit field specifying the operation to be
performed when the associated MatchPrefix matches an
interface's prefix or address. Values are:
1 the ADD operation
2 the CHANGE operation
3 the SET-GLOBAL operation
4 the PROPAGATE operation (new code).
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7.3 Mobile node Operation
When an HMIPv6-aware mobile node receives a router advertisement, it
should search for the MAP option. One or more options may be found
for different IP addresses or subnet prefixes.
A mobile node SHOULD register with the MAP having the highest
preference value. A MAP with a preference value of zero SHOULD NOT be
used for new local BUs (i.e. the mobile node can refresh existing
bindings but cannot create new ones). A mobile node MAY however
choose to register with one MAP over another depending on the value
received in the Distance field, provided that the preference value is
above zero.
A MAP option containing a valid lifetime value of zero means that
this MAP MUST NOT be selected by the MN. A valid lifetime of zero
indicates a MAP failure. When this option is received, a mobile node
MUST choose another MAP and create new bindings. Any existing
bindings with this MAP can be assumed to be lost.
If a multihomed mobile node has access to several ARs simultaneously
(on different interfaces), it SHOULD use an LCoA on the link defined
by the AR that advertises its current MAP.
A mobile node MUST store the received option(s) and choose at least
one MAP to register with. Storing the options is essential as they
will be compared to other options received later for the purpose of
the move detection algorithm.
If no MAP options are found in the router advertisement, the mobile
node MUST use the Mobile IPv6 protocol as specified in [1].
If the R flag is set, the mobile node MUST use its RCoA as the Home
Address when performing the MAP registration. RCoA is then bound to
the LCoA in the MAPÆs Binding Cache.
If the I flag is set the mobile node MAY choose to use RCoA as a
source address in its outgoing packets depending on whether location
privacy (with respect to the correspondent nodes and HA) is required
by the mobile node or user. This choice can be made by default
policies in the mobile node or configurable options by the user.
If the P flag is set, the mobile node MUST use RCoA as a source
address. This can be due to the network operatorÆs requirements of
not exposing certain prefixes to the external Internet.
The V flag indicates that the mobile node MUST tunnel its outbound
traffic to the MAP if its RCoA is used as a source address in
outbound packets. This flag is only useful if the P or I flags are
set. The aim of this flag is to avoid any potential ingress filtering
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problems in the ARs (in cases where the ingress filter cannot be
manually configured to allow an RCoA prefix).
A mobile node MAY choose to register with more than one MAP
simultaneously or use both MAP address and its own address as CoAs
simultaneously with different correspondent nodes provided the
setting of the P and I flags allow such choices.
8. Updating previous Anchor Points
When a mobile host moves into a new MAP domain, the mobile node may
send a BU to the previous MAP requesting to forward packets addressed
to the mobile nodeÆs new CoA.
9. Special optimisations for sending Binding Updates
In some link layers that require some L2 acquisition time before
sending each frame, it maybe useful for mobile nodes to encapsulate
the IP packet including a BU sent to the HA inside the IP packet
including a BU sent to the MAP. The decision on whether this
optimisation should be used or not is left to the mobile node
implementation, depending on the type of underlying L2 used for
transmission.
It should be noted however, that the use of such encapsulation may
cause extra signalling in case the Home registration was rejected by
the HA or MAP (e.g. if DAD failed and the mobile node is required to
provide a new Home address or if the MAP rejected the BU, forcing the
mobile node to re-register with the HA). Furthermore, the mobile node
might receive a binding acknowledgement from the MAP that contains a
lower lifetime than that received from the Home Agent. Hence, mobile
nodes should be careful when utilising this optimisation.
Therefore by default the MN SHOULD only send a BU containing its RCoA
to the HA and CNs after having received a positive local BU
acknowledgement from the MAP. This may be changed if it is proven
that the change will not impact the protocol behaviour.
10. Notes on MAP selection by the mobile node
HMIPv6 provides a flexible mechanism for local mobility management
within a visited network. As explained earlier a MAP can exist on any
level in a hierarchy including the AR. Several MAPs can be located
within a hierarchy independently of each other. In addition,
overlapping MAP domains are also allowed and recommended.
Both static and dynamic hierarchies are supported.
When the mobile node receives a router Advertisement including a MAP
option, it should perform actions according to the following movement
detection mechanisms. In a Hierarchical Mobile IP network such as the
one described in this draft, the mobile node SHOULD be:
Soliman, Castelluccia, El-Malki, Bellier [Page 18]
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- "Eager" to perform new bindings
- "Lazy" in releasing existing bindings
The above means that the mobile node should register with any "new"
MAP advertised by the AR (Eager). The method by which the mobile node
determines whether the MAP is a "new" MAP is described in section 5.
The mobile node should not release existing bindings until it no
longer receives the MAP option (or receives it with a lifetime of
zero) or the lifetime of its existing binding expires (Lazy). This
Eager-Lazy approach described above will assist in providing a
fallback mechanism in case of the failure of one of the MAP routers,
as it would reduce the time it takes for a mobile node to inform its
correspondent nodes and HA about its new COA.
10.1 MAP selection in a distributed-MAPs environment
The MN needs to consider several factors to optimally select one or
more MAPs, where several MAPs are available in the same domain.
There are no benefits foreseen in selecting more than one MAP and
forcing packets to be sent from the higher MAP down through a
hierarchy of MAPs. This approach may add forwarding delays and
eliminate the robustness of IP routing between the highest MAP and
the mobile node. Hence, allowing more than one MAP (ôaboveö the AR)
within a network should not imply that the mobile node forces packets
to be routed down the hierarchy of MAPs. However, placing more than
one MAP ôaboveö the AR can be used for redundancy and as an
optimisation for the different mobility scenarios experienced by
mobile nodes. The MAPs are used independently from each other by the
MN (e.g. each MAP is used for communication to a certain set of CNs).
In terms of the Distance based selection in a network with several
MAPs, a mobile node may choose to register with the furthest MAP to
avoid frequent re-registrations. This is particularly important for
fast mobile nodes that will perform frequent handoffs. In this
scenario, the choice of a further MAP would reduce the probability of
having to change a MAP and informing all correspondent nodes and the
HA. This specification does not provide an algorithm for the
distance-based MAP selection. However, such algorithm may be
introduced in future extensions utilising information about the speed
of mobility from lower layers.
In a scenario where several MAPs are discovered by the mobile node in
one domain, the mobile node may need some sophisticated algorithms to
be able to select the appropriate MAP. These algorithms would have
the mobile node speed as an input (for distance based selection)
combined with the preference field in the MAP option. However, this
specification proposes that the mobile node uses the following
algorithm as a default one, where other optimised algorithms may not
be available. The following algorithm is simply based on selecting
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the furthest possible MAP, provided that its preference value did not
reach the maximum value of 15. The mobile node operation is shown
below:
1. Receive and parse all MAP options
2. Arrange MAPs in a descending order, starting with the furthest MAP
(i.e. MAP option having largest Dist field)
3. Select first MAP in list
4. If the Preference value or the valid lifetime are set to zero,
select the following MAP in the list.
5. Repeat step (4) while new MAP options still exist.
Implementing the steps above would result in mobile nodes selecting
by default the most distant or ôhighestö available MAP by default.
This will continue to take place, until the preference value reduces
to zero. Following this, mobile nodes will start selecting another
MAP.
10.2 MAP selection in a flat mobility management architecture
Network operators may choose a flat architecture in some cases where
a Mobile IPv6 handover may be considered a rare event. In these
scenarios operators may choose to include the MAP function in ARs
only. The inclusion of the MAP function in ARs can still be useful to
reduce the time required to update all correspondent nodes and the
HA. In this scenario, a mobile node may choose a MAP (in the AR) as
an anchor point when performing a handoff. This kind of dynamic
hierarchy (or anchoring) is only recommended for cases where inter-AR
movement is not frequent.
11. Detection and recovery from MAP failures
This specification introduces a MAP which can be seen as a local Home
Agent in a visited network. A MAP, like a Home Agent, is a single
point of failure. If a MAP fails, its binding cache content will be
lost, resulting in loss of communication between mobile and
correspondent nodes. This situation may be avoided with the use of
more than one MAP on the same link and utilising some form of context
transfer protocol between them. Alternatively, future versions of the
Virtual Router Redundancy Protocol [10] may allow networks to recover
from MAP failures.
In cases where such protocols are not supported, the mobile node
would need to detect MAP failures. The mobile node can detect this
situation when it receives a router advertisement containing a MAP
option with a lifetime of zero. The mobile node should start the MAP
discovery process and attempt to register with another MAP. It will
also need to inform correspondent nodes and the Home Agent if its
RCoA has changed. Note that a new MAP may be able to provide the same
RCoA to the mobile node, e.g. if both MAPs advertise the same prefix
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in the MAP option. This would save the mobile node from updating
correspondent nodes and the Home Agent.
Access routers can be triggered to advertise a MAP option with a
lifetime of zero (indicating MAP failure) in different ways:
- By manual intervention.
- In a dynamic manner.
Dynamic detection of MAP failure can be done by simply pinging the
MAP regularly (e.g. every ten seconds). If no response is received
an AR may try to aggressively ping the MAP for a short period of time
(e.g. once every 5 seconds for 15 seconds); if no reply is received,
a MAP option may be sent with a valid lifetime value of zero.
This specification does not mandate a particular recovery mechanism.
However, any similar mechanism between the MAP and an AR MUST be
secured to allow for message authentication, integrity protection and
protection against replay attacks.
12. Security considerations
This specification introduces a new concept to Mobile IPv6, namely, a
Mobility Anchor Point that acts as a local Home Agent. It is crucial
that the security relationship between the mobile node and the MAP is
of strong nature; it MUST involve mutual authentication, integrity
protection and protection against replay attacks. Confidentiality may
be needed for payload traffic but is not required for binding updates
to the MAP. The absence of any of these protections may lead to
malicious mobile nodes impersonating other legitimate ones,
impersonating a MAP. Any of these attacks will undoubtedly cause
undesirable impacts to the mobile nodeÆs communication with all
correspondent nodes having knowledge of the mobile nodeÆs RCoA.
Three different relationships (related to securing binding updates)
need to be considered:
1) The mobile node û MAP
2) The mobile node û Home Agent
3) The mobile node - correspondent node
12.1 Mobile node û MAP security
HMIPv6 uses an additional registration between the mobile node and
its current MAP. As explained in this document, when a mobile node
moves into a new domain (i.e. served by a new MAP), it obtains an
RCoA, a LCoA and registers the binding between this two addresses
with the new MAP. The MAP then verifies whether the RCoA has not been
registered yet and if not creates a BCE with the RCoA and LCoA.
Whenever the mobile node gets a new LCoA, it needs to send a new
binding update that specifies the binding between RCoA and its new
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LCoA. This binding update needs to be authenticated otherwise any
host could send a BU for the mobile node's RCoA and hijack the mobile
node's packets. However since the RCoA is temporary and is not bound
to a particular node, a mobile node does not have to prove that it
owns its RCoA (as in Mobile IPv6) when it establishes a Security
Association with its MAP. A MAP only needs to make sure that when it
receives a BU for a RCoA, this BU was issued by the same mobile node
that established the Security Association.
The MAP does not need to know the identity of the mobile node nor its
Home Address. As a result the SA between the mobile node and the MAP
can be simply established using any key establishment protocols such
as IKE. A return routability test is not necessary.
The MAP needs to set the SA for the RCoA (not the LCoA). This can be
performed with IKE [6]. The mobile node uses its LCoA as source
address but specifies that the RCoA should be used in the SA. This is
achieved by using the RCoA as the client identity in IKE Phase 2
negotiation (Quick mode).
If a binding cache entry exists for a given RCoA, the MAP's IKE
policy check MUST point to the SA used to install the entry. If the
existing SA does not match the new SA which the MN is trying to
establish, then a MAP MUST reject the new SA establishment request
for such RCoA with an INVALID-ID-INFORMATION notification [6]. This
is to prevent two different mobile nodes from registering
(intentionally or not) the same RCoA. Upon receiving this
notification, the mobile node should generate a new RCoA and restart
the IKE negotiation.
Binding updates between the MAP and the mobile node MUST be protected
with either AH or ESP [7,8] in transport mode. When ESP is used, a
non-null authentication algorithm must be used.
12.2 Mobile node û correspondent node security
Mobile IPv6 [1] defines a return routability procedure that allows
mobile and correspondent nodes to authenticate binding updates and
acknowledgements. This specification does not impact the return
routability test defined in [1]. However, it is important to note
that mobile node implementers need to be careful when selecting the
source address of the HOTI and COTI messages defined in [1]. The
source address used in HOTI messages MUST be the mobile nodeÆs RCoA.
When sending this message, the mobile node need to be aware that the
message may need to be tunnelled to the MAP, which will de-capsulate
it and send it to the Home Agent (the destination address in the
tunnelled HOTI message). The decision about whether such message
should be tunnelled to the MAP or not, depends on the contents of the
V, P and I flags included in the MAP option. If either the P or I
flag is set, and the V flag is set, the mobile node must tunnel all
outgoing packets to the MAP. For the HOTI message, this would mean
Soliman, Castelluccia, El-Malki, Bellier [Page 22]
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that the message is tunnelled twice, once to the Home Agent, then
tunnelled again to the MAP.
If either the P or I flag is set, and the V flag is not set, the
mobile node does not need to tunnel these packets to the MAP. The
same conditions apply to the COTI message.
If neither the P or I flag is set in the MAP option, the mobile node
is not required to tunnel packets to the MAP. However, the HOTI and
COTI messages MUST be tunnelled through the MAP. This is needed to
avoid cases where ingress filtering in the AR is not configured to
support the use of RCoA as a source address. The MAP is required to
accept tunnelled packets from the mobile node independently of the
settings of the P, I and V flags.
12.3 Mobile node û Home Agent security
The security relationship between the mobile node and its Home Agent
is not impacted by this specification. The tunnel end point for the
Home Agent is the mobile nodeÆs RCOA. If either the P or I flag is
set, and the V flag is set, the mobile node must encapsulate packets
to the MAP. When applying this to the tunnel interface to the Home
Agent, it would mean that double encapsulation is necessary for both:
outgoing and incoming packets.
13. Acknowledgements
The authors would like to thank Conny Larsson (Ericsson) and Mattias
Pettersson (Ericsson) for their valuable input to this draft.
The authors would also like to thank the members of the French RNRT
MobiSecV6 project (BULL, France Telecom and INRIA) for testing the
first implementation and for their valuable feedback. The INRIA
HMIPv6 project is partially funded by the French Government.
In addition, the authors would like to thank the following members of
the working group in alphabetical order: Samita Chakrabarti (Sun),
Greg Daley (Monash University), Francis Dupont (Ernst-Bretagne),
Gopal Dommety (Cisco), Eva Gustaffson (Ericsson), Dave Johnson (Rice
University), Annika Jonsson (Ericsson), James Kempf (Docomo labs),
Martti Kuparinen (Ericsson) Fergal Ladley, Erik Nordmark (Sun),
Basavaraj Patil (Nokia) and Alper Yegin (Docomo labs) for their
comments on the draft.
14. Notice Regarding Intellectual Property Rights
see http://www.ietf.org/ietf/IPR/ERICSSON-hmipv6.txt
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15. References
Normative
[1] D. Johnson, C. Perkins and J. Arkko, "Mobility Support in
IPv6", draft-ietf-mobileip-ipv6-19.txt, November 2002.
[2] M. Crawford ôRouter Renumbering for IPv6ö. RFC 2984.
[3] S. Thomson and T. Narten "IPv6 Stateless Address
Autoconfiguration". RFC 2462.
[4] T. Narten, E. Nordmark and W. Simpson ô Neighbour Discovery for
IP version 6 ô. RFC 2461.
[5] S. Deering and B. Hinden, ôInternet Protocol version 6 (IPv6)
specificationö. RFC 2460
[6] D. Harkins and D. Carrel, ôThe Internet Key Exchange (IKE)ö.
RFC 2409.
[7] S. Kent and R. Atkinson, ôIP Authentication Headerö. RFC 2402
[8] S. Kent and R. Atkinson, ôIP Encapsulating Security Payloadö.
RFC 2406
[9] S. Kent and R. Atkinson, ôSecurity Architecture for the
Internetö. RFC 2401
[10] A. Conta and S. Deering, ôGeneric Packet Tunneling in IPv6
Specificationö RFC 2473.
[11] S. Bradner, ôKeywords to use in RFCs to Indicate Requirement
Levelsö. RFC2119
Non-Normative
[10] S. Knight, et al, ôVirtual Router Redundancy Protocolö.
RFC 2338.
[11] K. ElMalki, Editor, et al, "Low latency Handoffs in Mobile
IPv4". draft-ietf-mobileip-lowlatency-handoffs-v4-00. work
in progress.
[12] R. Koodli, Editor, et al,"Fast Handovers for Mobile IPv6",
draft-ietf-mobileip-fast-mipv6-05.txt. Work in progress.
[13] K. ElMalki and H. Soliman, ôSimultaneous Bindings for Mobile
IPv6 Fast Handoffsö. draft-elmalki-mobileip-bicasting-v6-
01. Work in progress.
Soliman, Castelluccia, El-Malki, Bellier [Page 24]
INTERNET-DRAFT HMIPv6 October,2002
[14] P. Ferguson and D. Senie, ôNetwork Ingress Filtering: Defeating
Denial of Service Attacks which employ IP Source Address
Spoofingö. RFC2267
16. Authors' Addresses
The working group can be contacted via the current chairs:
Basavaraj Patil Phil Roberts
Nokia Corporation Megisto Systems,Inc
6000 Connection Drive 20251 Century Blvd
Irving, TX 75039 Germantown, MD 20874
USA USA
Phone: +1 972-894-6709 Phone: +1 301-444-1700
EMail: Raj.Patil@nokia.com EMail: proberts@megisto.com
Fax : +1 972-894-5349 Fax: +1 301-515-3675
Questions about this memo can also be directed to:
Hesham Soliman
Ericsson Radio Systems AB
Torshamnsgatan 23,
Kista, Stockholm 16480
SWEDEN
Phone: +46 8 4046619
Fax: +46 8 4047020
E-mail: Hesham.Soliman@era.ericsson.se
Claude Castelluccia
INRIA Rhone-Alpes
655 avenue de l'Europe
38330 Montbonnot Saint-Martin
France
email: claude.castelluccia@inria.fr
phone: +33 4 76 61 52 15
fax: +33 4 76 61 52 52
Karim El Malki
Ericsson Radio Systems AB
LM Ericssons Vag. 8
126 25 Stockholm
SWEDEN
Phone: +46 8 7195803
Fax: +46 8 7190170
E-mail: Karim.El-Malki@era.ericsson.se
Soliman, Castelluccia, El-Malki, Bellier [Page 25]
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Ludovic Bellier
INRIA Rhone-Alpes
655 avenue de l'Europe
38330 Montbonnot Saint-Martin
France
email: ludovic.bellier@inria.fr
phone: +33 4 76 61 52 15
fax: +33 4 76 61 52 52
17. Appendix A û Fast Mobile IPv6 Handovers and HMIPv6
Fast Handovers are required to ensure that the layer 3 (Mobile IP)
handover delay is minimised, thus also minimising and possibly
eliminating the period of service disruption which normally occurs
when a mobile node moves between two ARs. This period of service
disruption usually occurs due to the time required by the mobile node
to update its HA using Binding Updates after it moves between ARs.
During this time period the mobile node cannot resume or continue
communications. The mechanism to achieve Fast Handovers with Mobile
IPv6 is described in [12] and is briefly summarised here. This
mechanism allows the anticipation of the layer 3 handover such that
data traffic can be redirected to the mobile nodeÆs new location
before it moves there.
While the mobile node is connected to its old Access Router (oAR) and
is about to move to a new Access Router (nAR), the Fast Handovers in
Mobile IPv6 requires in sequence:
1) the mobile node to obtain a new care-of address at the nAR while
connected to the oAR
2) New CoA to be used at nAR case: the mobile node to send a F-BU
(Fast BU) to its old anchor point (i.e. oAR) to update its binding
cache with the mobile nodeÆs new CoA while still attached to oAR
3) The old anchor point (i.e. oAR) to start forwarding packets
destined for the mobile node to the mobile nodeÆs new CoA at nAR
(or old CoA tunnelled to nAR if new CoA is not applicable).
4) Old CoA to be used at nAR case: the mobile node to send a F-BU
(Fast BU) to its old anchor point (i.e. oAR), after it has moved
and attached to nAR, in order to update its binding cache with the
mobile nodeÆs new CoA.
The mobile node or oAR may initiate the Fast Handover procedure by
using wireless link-layer information or link-layer ôtriggersö which
inform that the mobile node will soon be handed off between two
wireless access points respectively attached to oAR and nAR. If the
ôtriggerö is received at the mobile node, the mobile node will
initiate the layer-3 handover process by sending a Proxy Router
Solicitation message to oAR. Instead if the ôtriggerö is received at
oAR then it will transmit a Proxy Router Advertisement to the
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appropriate mobile node, without the need for solicitations. The
basic Fast Handover message exchanges are illustrated in Figure A.1.
+-----------+ 1a. HI +-----+
| | ---------------->| nAR |
| oAR | 1b. HAck | |
+-----------+ <--------------- +-----+
^ | ^
(2a. RtSolPr) | | 2b |
| | Pr | 3. Fast BU (F-BU)
| | RtAdv | 4. Fast BA (F-BACK)
| v v
+------------+
| MN |
+------------+ - - - - - ->
Movement
Figure A.1 û Fast Mobile IPv6 Handover Protocol
The mobile node obtains a new care-of address while connected to oAR
by means of router advertisements containing information from the nAR
(Proxy Router Advertisement which may be sent due to a Proxy Router
Solicitation). The oAR will validate the mobile nodeÆs new CoA by
sending a Handover Initiate (HI) message to the nAR. The new CoA sent
in the HI message is formed by appending the mobile nodeÆs ôcurrentö
interface identifier to the nARÆs prefix. Based on the response
generated in the Handover Acknowledge (HAck) message, the oAR will
either generate a tunnel to the mobile nodeÆs new CoA (if the address
was valid) or generate a tunnel to the nARÆs address (if the address
was already in use on the new subnet). If the address was already in
use on the new subnet it is assumed that there will be no time to
perform another attempt to configure the mobile node with a CoA on
the new link, so the nAR will generate a host route for the mobile
node using its old CoA. Note that message 1a may precede message 2b
or occur at the same time.
In [12], the ARs act as local Home Agents which hold binding caches
for the mobile nodes and receive Binding Updates. This makes these
ARs function like the MAP specified in this document. Also, it is
quite possible that the ARs are not directly connected, but
communicate through an aggregation router. Such an aggregation router
is therefore also an ideal position for the MAP functionality. These
are two ways of integrating the HMIPv6 and Fast Handover mechanisms.
The first involves placing MAPs in place of the ARs which is a
natural step. The second scenario involves placing the MAP in an
aggregation router ôaboveö the ARs. In this case, [12] specifies
forwarding of packets between oAR and nAR. This could be inefficient
in terms of delay, bandwidth efficiency since packets will traverse
the MAP-oAR link twice and packets arriving out of order at the
mobile node. Using the MAP in the aggregation router would improve
Soliman, Castelluccia, El-Malki, Bellier [Page 27]
INTERNET-DRAFT HMIPv6 October,2002
the efficiency of Fast Handovers which could make use of the MAP to
redirect traffic, thus saving delay and bandwidth between the
aggregation router and the oAR.
+---------+
| MAP |
+-------------->| |
| +---------+
| | ^
| 1a. HI | |
| | |
| | | 1b. HAck
| v |
+---------+ | +---------+
| | | | nAR |
| oAR | | | |
+---------+ | +---------+
^ | |
(2a. RtSolPr) | | 2b |
| | Pr | 3. Fast BU (F-BU) from mobile node to
| | MAP
| | RtAdv | 4. Fast BA (F-BACK) from MAP to
| | | mobile node
| v v
+------------+
| MN | Movement
+------------+ - - - - - ->
Figure A.2 û Fast Mobile IPv6 Handover Protocol using HMIPv6
In Figure A.2, the HI/HAck messages now occur between the MAP and nAR
to check the validity of the newly requested care-of address and to
establish a temporary tunnel should the new care-of address not be
valid. Therefore the same functionality of the Fast Handover
procedure is kept but the anchor point is moved from the oAR to the
MAP.
As in the previous Fast Handover procedure, in the network-determined
case the layer-2 ôtriggersö at the oAR will cause the oAR to send a
Proxy Router Advertisement to the mobile node with the MAP option. In
the mobile-determined case this is preceded by a Proxy Router
Solicitation from the mobile node. The same layer-2 ôtriggerö at oAR
in the network-determined case could be used to independently
initiate Context Transfer (e.g. QoS) between oAR and nAR. In the
mobile-determined case the trigger at oAR could be replaced by the
reception of a Proxy Router Solicitation or F-BU. Context Transfer is
being worked on in the IETF Seamoby WG.
The combination of Fast Handover and HMIPv6 allows the anticipation
of the layer 3 handoff such that data traffic can be efficiently
redirected to the mobile nodeÆs new location before it moves there.
Soliman, Castelluccia, El-Malki, Bellier [Page 28]
INTERNET-DRAFT HMIPv6 October,2002
However it is not easy to determine the correct time to start
forwarding traffic from the MAP to the mobile nodeÆs new location,
which has an impact on how smooth the handoff will be. The same
issues arises in [12] with respect to when to start forwarding
between oAR and nAR. Packet loss will occur if this is performed too
late or too early with respect to the time in which the mobile node
detaches from oAR and attaches to nAR. Such packet loss is likely to
occur if the MAP updates its binding cache upon receiving the
ôanticipatedö F-BU, since it is not known when exactly the mobile
node will perform or complete the layer-2 handover to nAR relative to
when the mobile node transmits the F-BU. Also, some measure is needed
to support the case in which the mobile nodeÆs layer-2 handover
unexpectedly fails (after Fast Handover has been initiated) or when
the mobile node moves quickly back-and-forth between ARs (ping-pong).
Simultaneous bindings [13] provides a solution to these issues. In
[13] a new Simultaneous Bindings Flag is added to the Fast Binding
Update (F-BU) message and a new Simultaneous Bindings suboption is
defined for Fast Binding Acknowledgement (F-BAck) message. Using this
enhanced mechanism, upon layer-3 handover, traffic for the mobile
node will be sent from the MAP to both oAR and nAR for a certain
period thus isolating the mobile node from layer-2 effects such as
handover timing, ping-pong or handover failure and providing the
mobile node with uninterrupted layer-3 connectivity.
Soliman, Castelluccia, El-Malki, Bellier [Page 29]
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