Cisco WLC Mobile-IP Clients and DHCP Requests

[alexisveras]

We have clients that roam from building to building on our campus, and these clients maintain their same IP address with Mobile-IP. In certain situations however, the client will no longer have its traffic tunneled, and it will come over the subnet of the building it is in. One instance we can see this on is when a client is rebooted. 

When the comes over the subnet of the new building and asks the DHCP server if it can continue using the IP address, the DHCP server responds with a not acknowledge (NAK - wrong network) letting the client know it can no longer use this IP address. The client proceeds to request a new IP address and it is given one from the subnet it is on.

This behavior is fine, as we want mobile-IP to work for active and roaming clients. However, I'm having trouble finding a good reading for how mobile-IP decides a client should no longer have its traffic tunneled. I have seen this document: https://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/mobile_ip/mobil_ip.html#wp1029661 and this discussion: https://community.cisco.com/t5/wireless-mobility-documents/mobile-ip/ta-p/3135863#toc-hId--85869350 which explain mobile IP very well, but I can't seem to find something that explains under which circumstances will a client no longer have its traffic tunneled (when it reaches session timeout? idle timeout? a certain period of time?).

It would be also helpful to know if there are any CLI commands that can be used to see the status of a client that is roaming with mobile-IP or see if there are any errors. Any experts around on this topic? Thanks for any info that can be provided. 

[Flavio Miranda]

Hi

 You may find this helpful:

"

2.4.2.1. Algorithm 1

The first method of move detection is based upon the Lifetime field within the main body of the ICMP Router Advertisement portion of the Agent Advertisement. A mobile node SHOULD record the Lifetime received in any Agent Advertisements, until that Lifetime expires. If the mobile node fails to receive another advertisement from the same agent within the specified Lifetime, it SHOULD assume that it has lost contact with that agent. If the mobile node has previously received an Agent Advertisement from another agent for which the Lifetime field has not yet expired, the mobile node MAY immediately attempt registration with that other agent. Otherwise, the mobile node SHOULD attempt to discover a new agent with which to register.

2.4.2.2. Algorithm 2

   The second method uses network prefixes.  The Prefix-Lengths
   Extension MAY be used in some cases by a mobile node to determine
   whether or not a newly received Agent Advertisement was received on
   the same subnet as the mobile node's current care-of address.  If the
   prefixes differ, the mobile node MAY assume that it has moved.  If a
   mobile node is currently using a foreign agent care-of address, the
   mobile node SHOULD NOT use this method of move detection unless both
   the current agent and the new agent include the Prefix-Lengths
   Extension in their respective Agent Advertisements; if this Extension
   is missing from one or both of the advertisements, this method of
   move detection SHOULD NOT be used.  Similarly, if a mobile node is
   using a co-located care-of address, it SHOULD not use this method of
   move detection unless the new agent includes the Prefix-Lengths
   Extension in its Advertisement and the mobile node knows the network
   prefix of its current co-located care-of address.  On the expiration
   of its current registration, if this method indicates that the mobile
   node has moved, rather than re-registering with its current care-of
   address, a mobile node MAY choose instead to register with a the
   foreign agent sending the new Advertisement with the different
   network prefix.  The Agent Advertisement on which the new
   registration is based MUST NOT have expired according to its Lifetime
   field."

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