Mobile IPv4 Registration Revocation

Basic Mobile IP resource revocation is an IS-835-C initiative that defines the methods by which a
mobility agent (one that provides Mobile IP services to a mobile node) can notify the other mobility
agent of the termination of a registration due to administrative reasons or MIP handoff.

This feature is similar to the Cisco MobileIP Bind Update feature. When a mobile changes its point of
attachment (FA), or needs to terminate the session administratively, the HA sends a registration
revocation message to the old FA. The old FA tears down the session and sends a registration revocation
acknowledgement message to the HA. Additionally, if the PDSN/FA needs to terminate the session
administratively, the FA sends a registration revocation message to the HA. The HA deletes the binding
for the mobile, and sends a registration revocation acknowledgement to FA.
An HA configured to support registration revocation in Mobile IPv4 includes a revocation support
extension in all MIP RRP for the associated MIP RRQ from the PDSN that contained a valid registration
revocation extension. A registration for which the HA received a revocation support extension, and
responded with a subsequent revocation support extension, is considered revocable by the HA.
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The following sample call flow illustrates Mobile IP Resource Revocation (Registration phase):
Step 1 The MS originates a call and PPP session is up.
Step 2 The PDSN/FA has been configured to advertise MIPv4 registration revocation support. The PDSN/FA
sends advertisement with MIPv4 Registration revocation support bit “X” set.
Step 3 The PDSN/FA receives MIP RRQ from MN, includes STC attribute set to 2 in access-request during
FA-CHAP. While forwarding the RRQ to the HA, the revocation support extension is appended after the
MHAE. The I-bit in the revocation support extension will be set to 1 indicating that the MS would get
an explicit notification on revocation of the binding whenever necessary.
Step 4 The HA, upon receiving the MIP RRQ containing a revocation extension, will send back the MIP RRP
including a revocation support extension and setting the I-bit equal to the value received in the MIP
RRQ. In case of HA-CHAP (MN-AAA authentication), the STC attribute, with a value of 2, will be
included in the access-request sent to AAA.
Step 5 The PDSN receives the MIP RRP containing a revocation support extension, and the data flow is
considered to be revocable.
The following sample call flow illustrates Mobile IP Resource Revocation (HA initiated):
Step 1 Mobile starts a mobile IP data session with PDSN/FA (1).
Step 2 PDSN/FA (1) appends a registration revocation support extension to the mobile registration request and
forwards it to the HA.
Step 3 In response, the HA appends the registration revocation support extension to a registration reply, and
send it to PDSN/FA (1).
Step 4 PDSN-to-PDSN handoff occurs, and the Mobile re-starts a mobile IP data session with PDSN/FA (2).
Step 5 PDSN/FA(2) sends a registration request to the HA.
Step 6 The HA sends a registration response to PDSN/FA (2).
Step 7 The HA sends a Mobile IP resource revocation message to the PDSN/FA (1).
Step 8 PDSN/FA (1) sends a Mobile IP resource revocation acknowledgement to the HA, and terminates the
mobile IP data session for the mobile.
The following sample call flow illustrates a Mobile IP Resource Revocation (FA initiated revocation):
Step 1 The Mobile starts a mobile IP data session with the PDSN/FA.
Step 2 The PDSN/FA appends the registration revocation support extension to the mobile registration request,
and forwards it to the HA.
Step 3 In response, the HA appends the registration revocation support extension to a registration reply, and
sends it to the PDSN/FA.
Step 4 Some event occurs in the PDSN/FA, and the PDSN/FA decides to close the session.
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Step 5 The PDSN/FA sends a Mobile IP resource revocation message to the HA.
Step 6 The HA sends a Mobile IP resource revocation acknowledgement to the HA. The HA clears the binding
and the PDSN/FA clears the session.
I-bit Support
During the registration revocation phase, the I (Inform) bit notifies the mobile node (MN) of the revoked
data service in cases where the mobile node has more than one MobileIP flow. If, during the registration
phase, this bit is set to 1 by a mobility agent in the revocation support extension in the RRQ/RRP, it
indicates that the agent supports the use of the “I” bit in revocation messages.
In the current implementation, if MobileIP RRQ is received with I bit set in the revocation support
extension, then the HA also sets the I-bit to 1, and the I-bit can be used during the revocation phase.
When the HA initiates revocation (and if the I bit was negotiated), it sets the I bit to 1 in the Revocation
message if a binding is administratively released, and sets it to 0 if a inter- PDSN handoff is detected by
the HA. When revocation is initiated by the PDSN, and the revocation message has I-bit set to 1, then
the HA also sets the I-bit to 1 in the revocation ACK message.


Configuring MIPv4 Registration Revocation
To enable MIPv4 Registration Revocation feature on HA, perform the following tasks in global
configuration mode:
The following example illustrates the ip mobile home-agent revocation command:
Router(config)# ip mobile home-agent revoc timeout ?
<1-100> Wait time (default 3 secs)
Router(config)# ip mobile home-agent revoc retransmit ?
<0-100> Number of retries for a transaction (default 3)



Mobile IPv4 Resource Revocation Restrictions
The following list identifies the restrictions for Mobile IPv4 Resource Revocation feature for the current
release:
• The STC attribute received in access-accept during HA-CHAP (MN-AAA authentication) is
ignored, and the feature configuration on the Home Agent will take precedence.
• The Revocation message, Revocation ACK message, and Revocation support extension (not
protected by either FHAE or IPSec) will not be discarded, but will be processed. We recommend
that you configure an FA-HA security association on the Home Agent, or that an IPSec tunnel exists
between the FA and the HA.
Command Purpose
Step 1 Router(config)# ip mobile home-agent revocation Enables support for MIPv4 Registration Revocation
on the HA.
Step 2 Router(config)# ip mobile home-agent revocation
timeout 5 retransmit 6
(Optional) Sets the retransmit count and timeout
value for revocation messages.
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• Resource Revocation and Bind Update cannot be enabled simultaneously. Both are mutually
exclusive of each other.
• The Home Agent MIB is not updated with the Registration revocation information.
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Simultaneous Bindings
The Home Agent does not support simultaneous bindings for the following reason:
• When multiple flows are established for the same NAI, a different IP address is assigned to each
flow. Therefore, simultaneous binding is not required because its function is to maintain more than
one flow to the same IP address.