> Mobile-IP and Proxy-MIP Timer Considerations
> This appendix is intended to provide a brief explanation of the considerations for lifetime, idle, and absolute timer settings that must be understood when setting up a system in a Mobile-IP or Proxy-MIP environment. The focus of the document is to understand the call flow and understand the timer values that must be applied to make the system function in the most efficient manner.
> Call Flow SummaryCall Flow SummaryCall Flow Summary
> Important: Commands used in the examples in this section provide base functionality to the extent that the most common or likely commands and/or keyword options are presented. In many cases, other optional commands and/or keyword options are available. Refer to the Command Line Interface Reference for complete information regarding all commands.
> The following steps describe the call flow as regards the timers that affect a call initiated by the Mobile Node (MN).

> 1. | The call arrives at the system and A11 (or L2TP, for Closed RP interfaces) (or L2TP, for Closed RP interfaces) is processed successfully. The call arrives at the system and R6 isThe call arrives at the system and R6 is processed successfully.The GGSN receives a Create PDP Context Request Message

> 2. | PPP negotiation is started. At this point,PPP negotiation is started. At this point, since authentication is not performed the system does not have a username or password. So during the PPP phase, the system selects the default subscriber in the source context for a subscriber template (DNS, and timer settings can be configured in the default subscriber template). Once PPP is successfully established the system understands that the call is a Mobile IP call. since authentication is not performed the system does not have a username or password. So during the PPP phase, the system selects the default subscriber in the source context for a subscriber template (DNS, and timer settings can be configured in the default subscriber template). Once PPP is successfully established the system understands that the call is a Mobile IP call.The system determines the propertiesThe system determines the properties

> 3. | The new RRQ is accepted by the FA and sent to the HA. The HA authenticates the user and compares the requested lifetime to the configured MIP lifetime in the HA-service and the subscriber idle and absolute timeouts. If the MIP lifetime is lower it is be sent back to the mobile; if the MIP lifetime is higher the system sends back an RRQ accept with the lifetime set to 5 seconds less than the lower of the idle or absolute timeout for the user.

> The following CLI command sequence is used to configure the Mobile IP reg-lifetime in the HA service:
> configure
> context <host_name>
> ha-service <ha_service_name>
> reg-lifetime <value>
> end
> Timer Values and RecommendationsTimer Values and RecommendationsTimer Values and Recommendations
> The following table shows values that would be populated under a number of different configured scenarios.
> Sample Call Flow Timer Scenarios

> Scenario | 1 | 2 | 3 | 4 | 5 | 6 | 7
> Mobile Sub. MIP Lifetime | 600 | 600 | 600 | 600 | 600 | 600 | 600
> Source Context Default Sub-Source Context Default Sub-Absolute | 300 | 300 | 300 | 300 | 300 | 300 | 300
> Source Context Default Sub-Source Context Default Sub-Idle | 300 | 300 | 300 | 300 | 300 | 300 | 300
> FA-Service Advertise Reg-Lifetime | 400 | 400 | 400 | 400 | 400 | 400 | 400
> Mobile Sub. Profile AAA Context Timeout idle | 500 | 500 | 500 | 500 | 500 | 500 | 500
> HA-Service MIP Lifetime | 400 | 400 | 400 | 400 | 400 | 400 | 400
> Agent Advertisement Reg-Lifetime | 295 | 295 | 295 | 295 | 295 | 295 | 295
> Mobile Sub. MIP RRQ requested lifetime | 295 | 295 | 295 | 295 | 295 | 295 | 295
> FA MIP RRP Lifetime | 295 | 295 | 295 | 295 | 295 | 295 | 295
> FA MIP RRP | success | success | success | success | success | success | Lifetime too long

> ‌
> Based on the table above, the recommended guidelines are as follows:

> • | If you are going to use timeout idle settings for subscribers, it is recommended that you configure the timeout idle parameter in the source context default subscriber to a value that is less than or equal to the lowest timeout idle for any subscriber.

> • | If you are going to use timeout absolute settings for subscribers, it is recommended that you configure the timeout absolute in the source context default subscriber to a value that is less than or equal to the lowest timeout idle for any subscriber.

> Failure to follow these recommendations could result in lifetime too long failures when the FA processes the subscriber profileAPN template and finds an idle timeout that is less than the proposed MIP lifetime in the mobile RRQ.
> Controlling the Mobile IP Lifetime on a Per-Domain BasisControlling the Mobile IP Lifetime on a Per-Domain BasisControlling the Mobile IP Lifetime on a Per-Domain Basis
> The system does not support the configuration of the MIP lifetime timer on per- domain (context) basis. However, a domain-wide lifetime timer can be achieved by configuring the idle-timeout attribute for the default subscriber for each domain.
> Important: Mobile IP lifetime settings can be controlled on a per-domain basis only in deployments for which the idle timeout attribute for individual subscriber profiles is not used during operation.
> In this configuration, the value of the registration lifetime sent by the system in Agent Advertisements is selected by comparing the configured FA Agent Advertisement lifetime setting, and the idle and/or absolute timeout settings configured for the domain’s default subscriber. If the value of the idle and/or absolute timeout parameter is less than the Agent Advertisement lifetime, then the system provides a registration lifetime equal to 5 seconds less than the lowest timer value.
> If the idle timeout attribute is configured in individual subscriber profiles, per-domain lifetime control is not possible. In this case, the registration lifetime configured for the FA must be the lower of the two values.
> Important: Commands used in the examples in this section provide base functionality to the extent that the most common or likely commands and/or keyword options are presented. In many cases, other optional commands and/or keyword options are available. Refer to the Command Line Interface Reference for complete information regarding all commands.
> The following is an example CLI command sequence used to configure the Mobile IP lifetime on a per-domain basis.
> configure
> context <aaa_context_name>
> subscriber default
> ip context-name <abc>
> exit
> subscriber name <ptt.bigco.com>
> timeout idle <3605>
> ip context-name <abc>
> exit
> subscriber name <bigco.com>
> timeout idle <7205>
> ip context-name <abc>
> exit
> domain <ptt.bigco.com> default subscriber <ptt.bigco.com>
> domain <bigco.com> default subscriber <bigco.com>
> end
> configure
> context <ha_context_name>
> subscriber default
> exit ha-service <ha>
> idle-timeout-mode normal reg-lifetime <7200>
> end
> configure
> context <fa_context_name>
> fa-service <fa>
> advertise reg-lifetime <7200>
> end
> In the example above, two domains (ptt.bigco.com and bigco.com) are configured. The default subscribers are defined for the two domains respectively. The desired operation requires a Mobile IP lifetime of 1 hour (3600 secs) for the ptt.bigco.com domain, and a lifetime of 2 hours (7200 secs) for the bigco.com domain.
> Whenever a subscriber session belonging to the ptt.bigco.com domain arrives, the system uses a Mobile IP lifetime timer value equal to 5 seconds less than the idle timeout configured for the default subscriber because the configured value is less than the registration lifetime value configured for the Agent Advertisement. 5 seconds less than the configured value of 3605 seconds equals 3600 seconds which meets the desired operation.
> Whenever a subscriber session belonging to the bigco.com domain arrives, the system uses the configured registration lifetime value as the Mobile IP lifetime in Agent Advertisements because it is less than the configured idle timeout in the default subscriber’s profile.
> As a general rule, the registration lifetime value on the agent must be configured as the highest Mobile IP lifetime that is desired for a subscriber. (In the above example, it would be the subscriber bigco.com.)
> Another important factor to consider is that the idle timeout value should be reset on receipt of a renewal request. To support this operation, the system provides the idle-timeout-mode configurable in the HA service. The following modes are supported:

> • | normal: Resets the idle timeout value on receipt of Mobile IP user data and control signaling

> • | aggressive: Resets the idle timeout value on receipt of Mobile IP user data only (this is the default behavior)

> • | handoff: Resets the idle timeout value on receipt of Mobile IP user dataand upon inter-AGW handoff

> The following optional modifier is also supported:

> • | upstream-only: Only upstream user data (data from the mobile node) resets the idle timer for the session. This is disabled by default.

Cisco Systems Inc.
Tel: 408-526-4000
Fax: 408-527-0883