MIP4 Working Group Rajeev. Koodli
Internet-Draft Charles. Perkins
Intended status: Experimental Nokia Research Center
Expires: August 27, 2007 February 23, 2007
Mobile IPv4 Fast Handovers
draft-ietf-mip4-fmipv4-04.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
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.
This Internet-Draft will expire on August 27, 2007.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document adapts the Mobile IPv6 Fast Handovers to improve delay
and packet loss resulting from Mobile IPv4 handover operations.
Specifically, this document addresses movement detection, IP address
configuration and location update latencies during a handover. For
reducing the IP address configuration latency, the document proposes
that the new Care-of Address is always made to be the new access
router's IP address. Additional mechanisms may be defined in the
future versions of this document.
Koodli & Perkins Expires August 27, 2007 [Page 1]
Internet-Draft MIP4 Fast Handovers February 2007
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Factors Affecting Handover . . . . . . . . . . . . . . . . . . 4
4. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Operation . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Using Previous FA Notification Extension . . . . . . . . . . . 9
6. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Fast Binding Update (FBU) . . . . . . . . . . . . . . . . 9
6.2. Fast Binding Acknowledgment (FBAck) . . . . . . . . . . . 10
6.3. Router Solicitation for Proxy Advertisement (RtSolPr) . . 12
6.4. Proxy Router Advertisement (PrRtAdv) . . . . . . . . . . . 13
6.5. Inter-Access Router Messages . . . . . . . . . . . . . . . 16
6.5.1. Handover Initiate (HI) . . . . . . . . . . . . . . . . 16
6.5.2. Handover Acknowledge (HAck) . . . . . . . . . . . . . 17
7. Option Formats . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Link-Layer Address Option Format . . . . . . . . . . . . . 19
7.2. New IPv4 Address Option Format . . . . . . . . . . . . . . 20
7.3. New Router Prefix Information Option . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Normative References . . . . . . . . . . . . . . . . . . . 23
11.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
Intellectual Property and Copyright Statements . . . . . . . . . . 26
Koodli & Perkins Expires August 27, 2007 [Page 2]
Internet-Draft MIP4 Fast Handovers February 2007
1. Introduction
This document adapts the fast handover specification [rfc4068] to
IPv4 networks. The fast handover protocol specified in this document
is particularly interesting for operation over links such as IEEE 802
wireless links. Fast handovers are not typically needed for wired
media due to the relatively large delays attributable to establishing
new connections in today's wired networks. Mobile IPv4 [rfc3344]
registration messages are re-used (with new type numbers) in this
document to enable faster implementation using existing Mobile IPv4
software. This draft does not rely on link-layer triggers for
protocol operation, but performance will typically be enhanced by
using the appropriate triggers when they are available. This
document assumes that the reader is familiar with the basic operation
and terminology of Mobile IPv4 [rfc3344] and Fast Handovers for
Mobile IPv6 [rfc4068].
The active agents that enable continued packet delivery to a mobile
node (MN) are the access routers on the networks that the mobile node
connects to. Handover means that the mobile node changes its network
connection, and we consider the scenario in which this change means
change in access routers. The mobile node utilizes the access
routers as default routers in the normal sense, but also as partners
in mobility management. Thus, when the mobile node moves to a new
network, it processes handover-related signaling in order to identify
and develop a relationship with a new access router. In this
document, we call the previous access router PAR and the new access
router NAR, consistent with the terminology in [rfc4068]. Unless
otherwise mentioned, a PAR is also a Previous Foreign Agent (PFA) and
a NAR is also a New Foreign Agent (NFA).
On a particular network, a mobile node may obtain its IP address via
DHCP [rfc2131] (i.e., Co-located Care-of Address) or use the Foreign
Agent CoA. During a handover, the new CoA (NCoA) is always made to
be that of NAR. This allows a mobile node to receive and send
packets using its previous CoA (PCoA), so that delays resulting from
IP configuration (such as DHCP address acquisition delay) subsequent
to attaching to the new link are disengaged from affecting the
existing sessions.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Terminology
The terminology used in this document in based on [rfc4068] and
Koodli & Perkins Expires August 27, 2007 [Page 3]
Internet-Draft MIP4 Fast Handovers February 2007
[rfc3344]. We provide some definitions below for convenience.
Mobile Node (MN): A Mobile IPv6 host.
Access Point (AP): A Layer 2 device connected to an IP subnet that
offers wireless connectivity to an MN. An Access Point Identifier
(AP-ID) refers to the AP's L2 address. Sometimes, AP-ID is also
referred to as a Base Station Subsystem ID (BSSID).
Access Router (AR): The MN's default router.
Previous Access Router (PAR): The MN's default router prior to its
handover.
New Access Router (NAR): The MN's default router subsequent to its
handover.
Previous CoA (PCoA): The MN's Care of Address valid on PAR's
subnet.
New CoA (NCoA): The MN's Care of Address valid on NAR's subnet.
Handover: A process of terminating existing connectivity and
obtaining new IP connectivity.
(AP-ID, AR-Info) tuple: Contains an access router's L2 and IP
addresses, and the prefix valid on the interface to which the
Access Point (identified by AP-ID) is attached. The triplet
[Router's L2 address, Router's IP address, Prefix] is called "AR-
Info".
3. Factors Affecting Handover
Both the link-layer operations and IP layer procedures affect the
perceived handover performance. However, the overall performance is
also (always) a function of specific implementation of the technology
as well as the system configuration. This document only specifies IP
layer protocol operations. The purpose of this section is to provide
an illustration of events that affect handover performance, but it is
purely informative.
The IP layer handover delay and packet loss are influenced by
latencies due to movement detection, IP address configuration and
Mobile IP registration procedure. Movement detection latency comes
from the need to reliably detect movement to a new subnet. This is a
function of frequency of router advertisements as well as default
Koodli & Perkins Expires August 27, 2007 [Page 4]
Internet-Draft MIP4 Fast Handovers February 2007
agent reachability. IP address configuration latency depends on the
particular IP CoA being used. If co-located mode with DHCP is used,
the latency is quite likely going to be higher and unacceptable for
real-time applications such as Voice over IP. Finally, the Mobile IP
registration procedure needs a round-trip of delay between the Mobile
Node and its Home Agent over the Internet. This delay is incurred
after the mobile node performs movement detection and IP
configuration.
Underlying the IP operations are link-layer procedures. These are
clearly technology-specific. For instance in IEEE 802.11, the
handover operation typically involves scanning access points over all
available channels, selecting a suitable access point, and
associating with it. It may also involve performing access control
operations such as those specified in IEEE 802.1X [ieee-802.1x].
These delays contribute to the handover performance. Optimizations
are being proposed for standardization in IEEE, for instance see
[ieee-802.11r] and [ieee-802.21]. Together with appropriate
implementation techniques, these optimizations can provide the
required level of delay support at the link-layer for real-time
applications.
4. Protocol
4.1. Overview
The design of the protocol is the same as for Mobile IPv6 [rfc4068].
Readers should consult [rfc4068] for details, and here we provide a
summary.
The protocol avoids the delay due to movement detection and IP
configuration and disengages Mobile IP registration delay from the
time-critical path. The protocol provides the surrounding network
neighborhood information so that a mobile node can determine whether
it is moving to a new subnet even before the handover. The
information provided and the signaling exchanged between the local
mobility agents allows the mobile node to send and receive packets
immediately after handover. In order to disengage the Mobile IP
registration latency, the protocol provides routing support for the
continued use of a mobile node's previous CoA.
After a mobile node obtains its IPv4 care-of address, it builds a
neighborhood access point and subnet map using the Router
Solicitation for Proxy Advertisement (RtSolPr) and Proxy Router
Advertisement (PrRtAdv) messages. The mobile node may scan for
access points (APs) based on the configuration policy in operation
for its wireless network interface. If a scan results in a new AP
Koodli & Perkins Expires August 27, 2007 [Page 5]
Internet-Draft MIP4 Fast Handovers February 2007
discovery, the mobile node resolves the corresponding AP Identifier
to subnet information using the RtSolPr and PrRtAdv messages
mentioned above.
At some point, the mobile node decides to undergo handover. It sends
an FBU message to PAR from the previous link or from the new link.
FBU message enables creation of a binding between the mobile node's
previous CoA and the new CoA.
The coordination between the access routers is done by way of the
Handover Initiate (HI) and Handover Acknowledge (HAck) messages
defined in [rfc4068]. After these signals have been exchanged
between the previous and new access routers (PAR and NAR), data
arriving at PAR will be tunneled to NAR for delivery to the newly
arrived mobile node. The purpose of HI is to securely deliver the
routing parameters for establishing this tunnel. The tunnel is
created by the access routers in response to the delivery of the FBU
from the mobile node.
4.2. Operation
In response to a handover trigger or indication, the mobile node
sends a Fast Binding Update message to Previous Access Router (PAR)
(see Section Section 6.1). Depending on the Mobile IP mode of
operation, the PCoA is either the Home Address (in FA CoA mode) or
co-located CoA (in CCoA mode). The FBU message SHOULD be sent when
the mobile node is still connected to PAR. When sent in this
"predictive" mode, the fields in the FBU are used as follows:
"Home Address" field must be the PCoA (which can be either the
Home Address or the co-located CoA)
Home Agent field, even though redundant, must be set to PAR's IP
address
Care-of Address field must be the NAR's IP address discovered via
PrRtAdv message
Destination IP address must be PAR's IP address
Source IP address must be the PCoA (which can be either the Home
Address or the co-located CoA)
As a result of processing the FBU, PAR creates a binding between PCoA
and NAR's IP address in its routing table. The PAR sends an FBack
message (see Section Section 6.2) as a response to the mobile node.
Koodli & Perkins Expires August 27, 2007 [Page 6]
Internet-Draft MIP4 Fast Handovers February 2007
The timeline for the predictive mode of operation (adapted from
[rfc4068]) is shown in Figure Figure 1.
MN PAR NAR
| | |
|------RtSolPr------->| |
|<-----PrRtAdv--------| |
| | |
|------FBU----------->|--------HI--------->|
| |<------HAck---------|
| <--FBack---|--FBack---> |
| | |
disconnect forward |
| packets===============>|
| | |
| | |
connect | |
| | |
|--------- FBU --------------------------->|
|<=================================== deliver packets
| |<-----FBU-----------|
Figure 1: Predictive Fast Handover
The mobile node sends the FBU regardless of its previous transmission
when attachment to a new link is detected. This minimally allows NAR
to detect mobile node's attachment, but also the retransmission of
FBU when an FBack has not been received yet. When sent in this
"reactive" mode, the following fields in FBU are set differently
compared to the predictive mode:
Destination IP address must be NAR's IP address
Source IP address must be PCoA (either the Home Address or the co-
located CoA)
When NAR receives FBU, it may already have processed the HI message
and created a host route entry for the PCoA. In that case, NAR
should immediately forward arriving and buffered packets including
the FBAck message. In any case, NAR MUST forward the contents of
this message, starting from the Type field, to PAR, which means the
Source and Destination IP addresses in the new packet now contain the
IP addresses of NAR and PAR respectively.
Koodli & Perkins Expires August 27, 2007 [Page 7]
Internet-Draft MIP4 Fast Handovers February 2007
The reactive mode of operation (adapted from [rfc4068]) is
illustrated in Figure Figure 2.
MN PAR NAR
| | |
|------RtSolPr------->| |
|<-----PrRtAdv--------| |
| | |
disconnect | |
| | |
| | |
connect | |
|-----------FBU-------|------------------->|
| |<-----FBU-----------|
| |------FBack-------->|
| forward |
| packets===============>|
| | |
|<=================================== deliver packets
| |
Figure 2: Reactive Fast Handover
The Handover Initiate (HI) and Handover Acknowledge (HAck) messages
serve to establish a bidirectional tunnel between the routers to
support packet forwarding for PCoA. The tunnel itself is established
as a response to the FBU message. The PAR sends HI message with Code
= 0 when it receives FBU with source IP address set to PCoA. The PAR
sends HI with Code = 1 when it receives FBU with source IP address
not set to PCoA (i.e., when received from NAR). This allows NAR to
disambiguate HI message processing sent as a response to predictive
and reactive modes of operation. If NAR receives a HI message with
Code = 1, and it has already set up a host route entry and a reverse
tunnel for PCoA, it should silently discard the HI message.
The protocol provides an option for NAR to return NCoA for use by the
mobile node. When NAR can provide an NCoA for exclusive use of the
mobile node, the address is supplied in the HAck message. The PAR
includes this NCoA in FBack. Exactly how NAR manages the address
pool from which it supplies NCoA is not specified in this document.
Nevertheless, the MN should be prepared to use this address instead
of performing DHCP or similar operations to obtain an IPv4 address.
Even though the mobile node can obtain this NCoA from the NAR, it is
Koodli & Perkins Expires August 27, 2007 [Page 8]
Internet-Draft MIP4 Fast Handovers February 2007
unaware of the address at the time it sends an FBU. Hence, it binds
PCoA to NAR's IP address as before.
5. Using Previous FA Notification Extension
Sending FBU from the new link (i.e., reactive mode) is similar to
using the extension defined in [draft-mip4-ro]. However, with the
neighborhood information gathered using the proxy router messages
(see Section Section 6.3, Section Section 6.4), movement detection
and router discovery delays are avoided even in the reactive case.
The FBU and FBAck messages defined in this document can be naturally
used even when no neighborhood information is available.
6. Message Formats
6.1. Fast Binding Update (FBU)
The FBU format is bitwise identical to the Registration Request
format in [rfc3344]. The same destination port number, 434, is used,
but the FBU and FBAck messages in this specification have new message
type numbers.
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 |x|x|D|M|G|r|T|x| reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Agent |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
Figure 3: Fast Binding Update (FBU) Message
Koodli & Perkins Expires August 27, 2007 [Page 9]
Internet-Draft MIP4 Fast Handovers February 2007
Source address: The interface address from which the message is
sent. Either PCoA (co-located or Home Address), or NAR's IP
address (when forwarded from NAR to PAR).
Destination Address: The IP address of the Previous Access Router
or the New Access Router.
Source Port: variable
Destination port: 434
Type: To be assigned by IANA
Flags: See [rfc3344]. The 'S' and 'B' flags in [rfc3344] are
sent as zero, and ignored on reception.
reserved: Sent as zero, ignored on input
Lifetime: The number of seconds remaining before binding
expires. MUST NOT exceed 10 seconds.
Home Address: MUST be PCoA, which can either be the co-located
CoA or the Home Address
Home Agent: The Previous Access Router's global IP address
Care-of Address: The New Access Router's global IP address
Identification: a 64-bit number used for matching an FBU with
FBack. Identical to usage in [rfc3344]
Extensions: MUST contain the MN - PAR Authentication Extension
6.2. Fast Binding Acknowledgment (FBAck)
The FBAck format is bitwise identical to the Registration Reply
format in [rfc3344].
Koodli & Perkins Expires August 27, 2007 [Page 10]
Internet-Draft MIP4 Fast Handovers February 2007
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 | reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Agent |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
Figure 4: Fast Binding Acknowledgement (FBAck) Message
Source address: Typically copied from the destination address of
the FBU message
Destination Address: Copied from the Source IP address in FBU
message
Source Port: variable
Destination port: copied from the source port in FBU message
Type: To be assigned by IANA
Code: Indicates the result of processing FBU message. Code = 0
means Fast Binding Update accepted. Code = 1 means Fast
Binding Update accepted but NCoA is supplied as an extension.
reserved: Sent as zero, ignored on input
Lifetime: The granted number of seconds remaining before
binding expires.
Home Address: PCoA (i.e., either co-located CoA or Home
Address)
Home Agent: The Previous Access Router's global IP address
Koodli & Perkins Expires August 27, 2007 [Page 11]
Internet-Draft MIP4 Fast Handovers February 2007
Identification: a 64-bit number used for matching FBU. Copied
from the field in FBU for which this FBack is a reply.
Extensions: The PAR - MN Authentication extension MUST be
present. In addition, an NCoA option MUST be present when NAR
supplies the NCoA.
If the FBAck message indicates that the new care-of address is a
Foreign Agent care-of address [rfc3344], then the mobile node MUST
set the 'D' bit in its Registration Request message that it uses to
register the NCoA with its home agent.
6.3. Router Solicitation for Proxy Advertisement (RtSolPr)
Mobile Nodes send Router Solicitation for Proxy Advertisement in
order to prompt routers for Proxy Router Advertisements. All the
link-layer address options have the format defined in Section 7.1.
The message format and processing rules are identical to those
defined in [rfc4068].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype | Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 5: Router Solicitation for Proxy Advertisement (RtSolPr)
Message
IP Fields:
Source Address: An IP address assigned to the sending interface
Destination Address: The address of the Access Router or the
all routers multicast address.
Time-to-Live: At least 1. See [rfc1256].
Koodli & Perkins Expires August 27, 2007 [Page 12]
Internet-Draft MIP4 Fast Handovers February 2007
ICMP Fields:
Type: To be assigned by IANA
Code: 0
Checksum: The 16-bit one's complement of the one's complement
sum of the ICMP message, start ing with the ICMP Type. For
computing the checksum, the Checksum and the Reserved fields
are set to 0. See [rfc1256].
Subtype: To be assigned by IANA
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: MUST be set by the sender so that replies can be
matched to this Solicitation.
Valid Options:
New Access Point Link-layer Address: The link-layer address or
identification of the access point for which the MN requests
routing advertisement information. It MUST be included in all
RtSolPr messages. More than one such address or identifier can
be present. This field can also be a wildcard address (see
Section 7.1).
6.4. Proxy Router Advertisement (PrRtAdv)
Access routers send out Proxy Router Advertisement message
gratuitously if the handover is network-initiated or as a response to
RtSolPr message from a mobile node, providing the link-layer address,
IP address and subnet prefixes of neighboring routers. All the link-
layer address options have the format defined in Section 7.1.
The message format and processing rules are identical to those
defined in [rfc4068].
Koodli & Perkins Expires August 27, 2007 [Page 13]
Internet-Draft MIP4 Fast Handovers February 2007
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype | Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 6: Proxy Router Advertisement (PrRtAdv) Message
IP Fields:
Source Address: An IP address assigned to the sending interface
Destination Address: The Source Address of an invoking Router
Solicitation for Proxy Advertisement or the address of the node
the Access Router is instructing to handover.
Time-to-Live At least 1. See [rfc1256].
ICMP Fields:
Type: To be assigned by IANA
Code 0, 1, 2, 3 or 4. See below.
Checksum: The 16-bit one's complement of the one's complement
sum of the ICMP message, start- ing with the ICMP Type. For
computing the checksum, the Checksum and the Reserved fields
are set to 0. See [rfc1256].
Subtype: To be assigned by IANA.
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: Copied from Router Solicitation for Proxy
Advertisement or set to Zero if unsolicited.
Valid Options in the following order:
New Access Point Link-layer Address: The link-layer address or
identification of the access point is copied from RtSolPr
message. This option MUST be present.
Koodli & Perkins Expires August 27, 2007 [Page 14]
Internet-Draft MIP4 Fast Handovers February 2007
New Router's Link-layer Address: The link-layer address of the
Access Router for which this message is proxied for. This
option MUST be included when Code is 0 or 1.
New Router's IP Address: The IP address of NAR. This option
MUST be included when Code is 0 or 1.
New Router Prefix Information Option: The number of leading
bits that define the network number of the corresponding
Router's IP Address option (see above).
New CoA Option: MAY be present when PrRtAdv is sent
unsolicited. PAR MAY compute new CoA using NAR's prefix
information and the MN's L2 address, or by any other means. In
any case, the MN should be prepared to use this address instead
of performing DHCP or similar operations to obtain an IPv4
address.
A PrRtAdv with Code 0 means that the MN should use the [AP-ID, AR-
Info] tuple present in the options above. In this case, the Option-
Code field (see Section 7.1) in the New AP LLA option is 1,
reflecting the LLA of the access point for which the rest of the
options are related, and the Option-Code for the New Router's LLA
option is 3. Multiple tuples may be present.
A PrRtAdv with Code 1 means that the message is sent unsolicited. If
a New IPv4 option (see Figure 10) is present following the New Router
Prefix Information option (see Section 7.3), the MN SHOULD use the
supplied NCoA and send the FBU immediately or else stand to lose
service. This message acts as a network-initiated handover trigger.
The Option-Code field (see Section 7.1) in the New AP LLA option in
this case is 1 reflecting the LLA of the access point for which the
rest of the options are related.
A Proxy Router Advertisement with Code 2 means that no new router
information is present. The LLA option contains an Option-Code value
that indicates a specific reason (see Section 7.1).
A Proxy Router Advertisement with Code 3 means that new router
information is only present for a subset of access points requested.
The Option-Code values in the LLA option distinguish different
outcomes (see Section 7.1).
A Proxy Router Advertisement with Code 4 means that the subnet
information regarding neighboring access points is sent unsolicited,
but the message is not a handover trigger, unlike when the message is
Koodli & Perkins Expires August 27, 2007 [Page 15]
Internet-Draft MIP4 Fast Handovers February 2007
sent with Code 1. Multiple tuples may be present.
When a wildcard AP identifier is supplied in the RtSolPr message, the
PrRtAdv message should include any 'n' [Access Point Identifier,
Link-Layer Address option, Prefix Information Option] tuples
corresponding to the PAR's neighborhood.
6.5. Inter-Access Router Messages
6.5.1. Handover Initiate (HI)
The Handover Initiate (HI) is an ICMP message sent by an Access
Router (typically PAR) to another Access Router (typically NAR) to
initiate the process of a mobile node's handover.
The message format and processing rules are identical to those
defined in [rfc4068].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype |S|U| Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 7: Handover Initiate (HI) Message
IP Fields:
Source Address: The IP address of the PAR
Destination Address: The IP address of the NAR
Time-to-Live: At least 1. See [rfc1256].
ICMP Fields:
Type: To be assigned by IANA
Code: 0 or 1. See below
Koodli & Perkins Expires August 27, 2007 [Page 16]
Internet-Draft MIP4 Fast Handovers February 2007
Checksum: The 16-bit one's complement of the one's complement
sum of the ICMP message, start- ing with the ICMP Type. For
computing the checksum, the Checksum and the Reserved fields
are set to 0. See [rfc1256].
Subtype: To be assigned by IANA
S: Assigned address configuration flag. When set, this message
requests a new CoA to be returned by the destination. May be
set when Code = 0. MUST be 0 when Code = 1.
U: Buffer flag. When set, the destination SHOULD buffer any
packets towards the node indicated in the options of this
message. Used when Code = 0, SHOULD be set to 0 when Code = 1.
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: MUST be set by the sender so replies can be matched
to this message.
Valid Options:
Link-layer address of MN: The link-layer address of the MN that
is undergoing handover to the destination (i.e., NAR). This
option MUST be included so that the destination can recognize
the MN.
Previous Care of Address: The IP address used by the MN while
attached to the originating router. This option MUST be
included so that a host route can be established on the NAR.
New Care of Address: This option MAY be present when the MN
wishes to use a new IP address when connected to the
destination. When the 'S' bit is set, NAR MAY provide this
address in HAck, in which case t he MN should be prepared to
use this address instead of performing DHCP or similar
operations to obtain an IPv4 address.
6.5.2. Handover Acknowledge (HAck)
The Handover Acknowledgment message is a new ICMP message that MUST
be sent (typically by NAR to PAR) as a reply to the Handover Initiate
(HI) (see Section Section 6.5.1) message.
The message format and processing rules are identical to those
defined in [rfc4068].
Koodli & Perkins Expires August 27, 2007 [Page 17]
Internet-Draft MIP4 Fast Handovers February 2007
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype | Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 8: Handover Acknowledge (HAck) Message
IP Fields:
Source Address: Copied from the destination address of the
Handover Initiate Message to which this message is a response.
Destination Address: Copied from the source address of the
Handover Initiate Message to which this message is a response.
Time-to-Live: At least 1. See [rfc1256].
ICMP Fields:
Type: To be assigned by IANA
Code:
0: Handover Accepted
1: Handover Accepted, NCoA not valid
2: Handover Accepted, NCoA in use
3: Handover Accepted, NCoA assigned (used in Assigned
addressing)
4: Handover Accepted, NCoA not assigned
128: Handover Not Accepted, reason unspecified
129: Administratively prohibited
130: Insufficient resources
Checksum: The 16-bit one's complement of the one's complement
sum of the ICMP message, start- ing with the ICMP Type. For
computing the checksum, the Checksum and the Reserved fields
are set to 0. See [rfc1256].
Subtype: To be assigned by IANA.
Koodli & Perkins Expires August 27, 2007 [Page 18]
Internet-Draft MIP4 Fast Handovers February 2007
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: Copied from the corresponding field in the Handover
Initiate message this message is in response to.
Valid Options:
New Care of Address: If the 'S' flag in the HI message is set,
this option MUST be used to provide NCoA the MN should use when
connected to this router. This option MAY be included even
when 'S' bit is not set, e.g., Code 2 above. The MN should be
prepared to use this address instead of performing DHCP or
similar operations to obtain an IPv4 address.
The Code 0 is the expected average case of a handover being accepted
and the routing support provided for the use of PCoA. The rest of
the Code values pertain to the use of NCoA (which is common in
[rfc4068]). Code values 1 and 2 are for cases when the MN proposes
an NCoA and the NAR provides a response. Code 3 is when the NAR
provides NCoA (which could be the same as that proposed by the MN).
Code 4 is when the NAR does not provide NCoA, but instead provides
routing support for PCoA.
7. Option Formats
The options in this section are specified as extensions for the HI
and HAck messages, as well as for the PrRtSol and PrRtAdv messages.
7.1. Link-Layer Address Option 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 | Option-Code | LLA ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Link Layer Address Option Format
Fields:
Type: To be assigned by IANA
Koodli & Perkins Expires August 27, 2007 [Page 19]
Internet-Draft MIP4 Fast Handovers February 2007
Option-Code:
0: wildcard requesting resolution for all nearby access
points
1: Link-Layer Address of the New Access Point
2: Link-Layer Address of the MN
3: Link-Layer Address of the NAR
4: Link-Layer Address of the source of the RtSolPr or
PrRtAdv message
5: The access point identified by the LLA belongs to the
current interface of the router
6: No prefix information available for the access point
identified by the LLA
7: No fast handovers support available for the access point
identified by the LLA
Length: The length of the option (including the Type, Length
and Option-Code fields) in units of 8 octets.
Link-Layer Address: The variable length link-layer address.
The content and format of this field (including byte and bit
ordering) depends on the specific link-layer in use.
Depending on the size of the individual LLA option, appropriate
padding MUST be used to ensure that the entire option size is a
multiple of 8 octets.
7.2. New IPv4 Address Option Format
This option is used to provide the new router's IPv4 address or the
NCoA in PrRtAdv, as well as PCoA and NCoA in HI and HAck messages.
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 | Option-Code | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: New IPv4 Address Option Format
Koodli & Perkins Expires August 27, 2007 [Page 20]
Internet-Draft MIP4 Fast Handovers February 2007
Fields:
Type: To be assigned by IANA
Length: The length of the option (including the Type, Length
and Option-Code fields) in units of 8 octets.
Option-Code:
1: Previous CoA
2: New CoA
3: NAR's IP Address
Reserved: Set to zero.
New IPv4 Address: NAR's IPv4 address or the NCoA assigned by
NAR.
7.3. New Router Prefix Information Option
This option is used in the PrRtAdv message.
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 | Option-Code | Prefix-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: New Router Prefix Information Option Format
Fields:
Type: To be assigned by IANA
Length: The length of the option (including the Type, Length
and Option-Code fields) in units of 8 octets.
Option-Code: 0
Prefix-Length The number of leading bits that define the
network number of the corresponding Router's IP Address option.
Koodli & Perkins Expires August 27, 2007 [Page 21]
Internet-Draft MIP4 Fast Handovers February 2007
Reserved: Set to zero.
8. Security Considerations
As outlined in [rfc4068], the following vulnerabilities are
identified and the solutions mentioned.
Insecure FBU:
Failure to protect the FBU message could result in packets meant for
an address being stolen or redirected to some unsuspecting node.
This concern is similar to that in Mobile Node and Home Agent
relationship.
Hence, the FBU and FBack messages MUST be protected using a security
association shared between a mobile node and its access router. In
particular, the MN - PAR Authentication Extension MUST be present in
each of these messages. This document does not specify how the
security association is established between a MN and the AR/FA.
Secure FBU, malicious or inadvertent redirection:
Even if the MN - PAR authentication extension is present in an FBU, a
MN may indevertently or maliciously attempt to bind its PCoA to an
unintended address on NAR's link, and cause traffic flooding to an
unsuspecting node.
This vulnerability is avoided by always binding the PCoA to the NAR's
IP address, even when the NAR supplies an NCoA to use for the MN. It
is still possible to jam NAR's buffer with redirected traffic.
However, the handover state corresponding to the MN's PCoA has a
finite lifetime, and can be configured to be a few multiples of the
anticipated handover latency. Hence, the extent of this
vulnerability is small.
Communication between the access routers:
The access routers communicate using HI and HAck messages in order to
establish a temporary routing path for the MN undergoing handover.
This message exchange needs to be secured to ensure routing updates
take place as intended.
The HI and HAck messages need to be secured using a pre-existing
security association between the access routers to ensure at least
message integrity and authentication, and should also include
Koodli & Perkins Expires August 27, 2007 [Page 22]
Internet-Draft MIP4 Fast Handovers February 2007
encryption.
9. IANA Considerations
All the messages and the option formats specified in this document
require Type assignment from IANA. Specifically, the Types, Sub-
types and the Codes need assignment from ICMP, Mobile IP and
Experimental Mobility Type [rfc4065] registries.
10. Acknowledgement
Thanks to all those who expressed interest in having a Fast Handovers
for Mobile IPv4 protocol along the lines of [rfc4068]. Thanks to
Vijay Devarapalli, Keng Leung for their review and input. Kumar
Viswanath and Uday Mohan implemented an early version of this
protocol. Many thanks to Alex Petrescu for his thorough review that
improved this document.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[rfc1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991.
[rfc3344] Perkins (Editor), C., "IP Mobility Support for IPv4",
RFC 3344, August 2002.
[rfc4065] Kempf, J., "Instructions for Seamoby and Experimental
Mobility Protocol IANA Allocations", RFC 4065, July 2005.
[rfc4068] Koodli (Editor), R., "Fast Handovers for Mobile IPv6",
RFC 4068, July 2005.
11.2. Informative References
[draft-mip4-ro]
Perkins, C. and D. Johnson, "Route Optimization in Mobile
IP (work in progress). Internet Draft, Internet
Engineering Task Force", February 2000.
[ieee-802.11r]
Koodli & Perkins Expires August 27, 2007 [Page 23]
Internet-Draft MIP4 Fast Handovers February 2007
"IEEE Standard forLocal and Metropolitan Area Networks:
Fast Roaming/Fast BSS Transition, the IEEE Task Group TGr.
Technical report, IEEE.".
[ieee-802.1x]
"IEEE Standard for Local and Metropolitan Area Networks:
Port-Based Network Access Control. Technical report,
IEEE.".
[ieee-802.21]
"The IEEE 802.21 group. http://www.ieee802.org/21.".
[rfc2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
Appendix A. Change Log
Addressed the following Last Call and subsequent reviews:
Provided all the Code values in PrRtAdv message to cover various
cases involving neighborhood discovery. Harmonized the option
formats with [rfc4068].
Added the Terminology Section
Added text regarding FBU message flags 'S' and 'B'
Revised text in Security Considerations
Clarified text in different places based on ML comments (including
"forwarding", MN's use of assigned addresses in lieu of DHCP, and
so on.)
Clarified using ICMPv4 checksum for RtSolPr, PrRtAdv, HI and HAck
Added Figures illustrating predictive and reactive handovers
Added references to IEEE 802.21 and IEEE 802.11r
All id nits (attempt to move from LaTex to xml turned out to be
quite a task, sigh..)
Koodli & Perkins Expires August 27, 2007 [Page 24]
Internet-Draft MIP4 Fast Handovers February 2007
Authors' Addresses
Rajeev Koodli
Nokia Research Center
975 Page Mill Road, 200
Palo Alto, CA 94304
USA
Email: rajeev.koodli@nokia.com
Charles Perkins
Nokia Research Center
975 Page Mill Road, 200
Palo Alto, CA 94304
USA
Email: charles.perkins@nokia.com
Koodli & Perkins Expires August 27, 2007 [Page 25]
Internet-Draft MIP4 Fast Handovers February 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Koodli & Perkins Expires August 27, 2007 [Page 26]
