Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options that they do not recognize
and continue processing the rest of the message.
Including the source LLA option allows the receiver to record the
sender’s L2 address so that neighbor discovery can be avoided when
the receiver needs to send packets back to the sender (of the RtSolPr
message).
When a wildcard is used for a New Access Point LLA, no other New
Access Point LLA options must be present.
A Proxy Router Advertisement (PrRtAdv) message should be received by
the MN in response to a RtSolPr. If such a message is not received
in a timely manner (no less than twice the typical round trip time
(RTT) over the access link or 100 milliseconds if RTT is not known),
it SHOULD resend the RtSolPr message. Subsequent retransmissions can
be up to RTSOLPR_RETRIES, but MUST use an exponential backoff in
which the timeout period (i.e., 2xRTT or 100 milliseconds) is doubled
prior to each instance of retransmission. If Proxy Router
Advertisement is not received by the time the MN disconnects from the
PAR, the MN SHOULD send an FBU immediately after configuring a new
CoA.
When RtSolPr messages are sent more than once, they MUST be rate
limited with MAX_RTSOLPR_RATE per second. During each use of a
RtSolPr, exponential backoff is used for retransmissions.
6.1.2. Proxy Router Advertisement (PrRtAdv)
Access routers send Proxy Router Advertisement messages gratuitously
if the handover is network-initiated or as a response to a RtSolPr
message from an MN, 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 6.4.3.
IP Fields:
Source Address
MUST be the Link-Local Address assigned to the
interface from which this message is sent.
Destination Address
The Source Address of an invoking Router
Solicitation for a Proxy Advertisement or the
address of the node the Access Router is
instructing to handover.
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: Proxy Router Advertisement (PrRtAdv) Message
Hop Limit 255. See RFC 2461 [6].
Authentication Header
If a Security Association for the IP Authentication
Header exists between the sender and the
destination address, the sender SHOULD include this
header. See RFC 2402 [5].
ICMP Fields:
Type The Experimental Mobility Protocol Type. See RFC
4065 [4].
Code 0, 1, 2, 3 or 4. See below.
Checksum The ICMPv6 checksum.
Subtype 3
Reserved MUST be set to zero by the sender and ignored by
the receiver.
Identifier Copied from the Router Solicitation for Proxy
Advertisement or set to Zero if unsolicited.
Valid Options in the following order:
Source Link-Layer Address
When known, the Link-Layer Address of the sender
SHOULD be included using the Link-Layer Address
option. See the LLA option format below.
New Access Point Link-Layer Address
The Link-Layer Address or identification of the
access point is copied from the RtSolPr message.
This option MUST be present.
New Router’s Link-Layer Address
The Link-Layer Address of the Access Router for
which this message is proxied. 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.
Specifies the prefix of the Access Router for which
the message is proxied and is used for address
auto-configuration. This option MUST be included
when Code is 0 or 1. However, when this prefix is
the same as that used in the New Router’s IP
Address option (above), the Prefix Information
option need not be present.
New CoA Option
MAY be present when a PrRtAdv is sent unsolicited.
PAR MAY compute a new CoA using NAR’s prefix
information and the MN’s L2 address, or by any
other means.
Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognize and
continue processing the message.
Currently, Code values 0, 1, 2, 3 and 4 are defined.
A Proxy Router Advertisement with Code 0 means that the MN should use
the [AP-ID, AR-Info] tuple (present in the options above) for
movement detection and NCoA formulation. In this case, the Option-
Code field in the New Access Point LLA option is 1, reflecting the
LLA of the access point for which the rest of the options are
related. Multiple tuples may be present.
A Proxy Router Advertisement with Code 1 means that the message is
sent unsolicited. If a New CoA option is present following the New
Router Prefix Information option, 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; see Section
3.3. The Option-Code field in the New Access Point LLA option (see
below) 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. Each New Access Point LLA option contains an
Option-Code value (described below) that indicates a specific
outcome.
- When the Option-Code field in the New Access Point LLA option
is 5, handover to that access point does not require a change
of CoA. No other options are required in this case.
- When the Option-Code field in the New Access Point LLA option
is 6, the PAR is not aware of the Prefix Information requested.
The MN SHOULD attempt to send an FBU as soon as it regains
connectivity with the NAR. No other options are required in
this case.
- When the Option-Code field in the New Access Point LLA option
is 7, it means that the NAR does not support fast handover.
The MN MUST stop fast handover protocol operations. No other
options are required in this case.
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 field values (defined above including a value of 1)
distinguish different outcomes for individual access points.
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
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.
6.2. Inter-Access Router Messages
6.2.1. Handover Initiate (HI)
The Handover Initiate (HI) is an ICMPv6 message sent by an Access
Router (typically PAR) to another Access Router (typically NAR) to
initiate the process of a MN’s handover.
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 6: Handover Initiate (HI) Message
IP Fields:
Source Address
The IP address of the PAR.
Destination Address
The IP address of the NAR.
Hop Limit 255. See RFC 2461 [6].
Authentication Header
The authentication header MUST be used when this
message is sent. See RFC 2402 [5].
ICMP Fields:
Type The Experimental Mobility Protocol Type. See RFC
4065 [4].
Code 0 or 1. See below
Checksum The ICMPv6 checksum.
Subtype 4
S flag 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 flag Buffer flag. When set, the destination SHOULD
buffer any packets moving toward 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 SHOULD be included
so that a host route can be established if
necessary.
New Care of Address
The IP address the MN wishes to use when connected
to the destination. When the `S’ bit is set, the
NAR MAY assign this address.
The PAR uses a Code value of 0 when it processes an FBU with PCoA as
a source IP address. The PAR uses a Code value of 1 when it
processes an FBU whose source IP address is not PCoA.
If a Handover Acknowledge (HAck) message is not received as a
response in a short time period (no less than twice the typical RTT
between source and destination, or 100 milliseconds if RTT is not
known), the Handover Initiate SHOULD be resent. Subsequent
retransmissions can be up to HI_RETRIES, but MUST use exponential
backoff in which the timeout period (i.e., 2xRTT or 100 milliseconds)
is doubled during each instance of retransmission.
6.2.2. Handover Acknowledge (HAck)
The Handover Acknowledgment message is a new ICMPv6 message that MUST
be sent (typically by NAR to PAR) as a reply to the Handover Initiate
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype | Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 7: 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.
Hop Limit 255. See RFC 2461 [6].
Authentication Header
The authentication header MUST be used when this
message is sent. See RFC 2402 [5].
ICMP Fields:
Type The Experimental Mobility Protocol Type. See RFC
4065 [4].
Code
0: Handover Accepted, NCoA valid
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
(used in Assigned addressing)
128: Handover Not Accepted, reason unspecified
129: Administratively prohibited
130: Insufficient resources
Checksum The ICMPv6 checksum.
Subtype 5
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 to which this message is a
response.
Valid Options:
New Care of Address
If the S flag in the Handover Initiate 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 the `S’ bit is
not set, e.g., Code 2 above.
Upon receiving an HI message, the NAR MUST respond with a Handover
Acknowledge message. If the `S’ flag is set in the HI message, the
NAR SHOULD include the New Care of Address option and a Code 3.
The NAR MAY provide support for PCoA (instead of accepting or
assigning NCoA), establish a host route entry for PCoA, and set up a
tunnel to the PAR to forward MN’s packets sent with PCoA as a source
IP address. This host route entry SHOULD be used to forward packets
once the NAR detects that the particular MN is attached to its link.
When responding to an HI message containing a Code value 1, the Code
values 1, 2, and 4 in the HAck message are not relevant.
Finally, the new access router can always refuse handover, in which
case it should indicate the reason in one of the available Code
values.
6.3. New Mobility Header Messages
Mobile IPv6 uses a new IPv6 header type called Mobility Header [3].
The Fast Binding Update, Fast Binding Acknowledgment, and Fast
Neighbor Advertisement messages use the Mobility Header.
6.3.1. Fast Binding Update (FBU)
The Fast Binding Update message is identical to the Mobile IPv6
Binding Update (BU) message. However, the processing rules are
slightly different.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Fast Binding Update (FBU) Message
IP fields:
Source Address
The PCoA or NCoA
Destination Address
The IP address of the Previous Access Router
A flag MUST be set to one to request that PAR send a Fast
Binding Acknowledgment message.
H flag MUST be set to one. See RFC 3775 [3].
L flag See RFC 3775 [3].
K flag See RFC 3775 [3].
Reserved This field is unused. MUST be set zero.
Sequence Number
See RFC 3775 [3].
Lifetime See RFC 3775 [3].
Mobility Options
MUST contain an alternate CoA option set to the
NCoA when an FBU is sent from PAR’s link.
The MN sends an FBU message any time after receiving a PrRtAdv
message. If the MN moves prior to receiving a PrRtAdv message, it
SHOULD send an FBU to the PAR after configuring NCoA on the NAR
according to Neighbor Discovery and IPv6 Address Configuration
protocols.
The source IP address is PCoA when the FBU is sent from PAR’s link,
and the source IP address is NCoA when sent from NAR’s link. When
the FBU is sent from NAR’s link, it SHOULD be encapsulated within an
FNA.
The FBU MUST also include the Home Address Option, and the Home
Address is PCoA. An FBU message MUST be protected so that PAR is
able to determine that the FBU message is sent by a genuine MN.
6.3.2. Fast Binding Acknowledgment (FBack)
The Fast Binding Acknowledgment message is sent by the PAR to
acknowledge receipt of a Fast Binding Update message in which the ’A’
bit is set. The Fast Binding Acknowledgment message SHOULD NOT be
sent to the MN before the PAR receives a HAck message from the NAR.
The Fast Binding Acknowledgment MAY also be sent to the MN on the old
link.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |K| Reserved |