Controller Based WLANs

Question : How to troubleshoot when RAP is not getting an IP from L2tp pool?

Resolution :

Please check if 4500 traffic is hitting the controller.
If 4500 traffic is hitting the controller and the traffic and the return traffic is properly synced in the datapath session table. Then check if ISAKMP SA is formed.

If ISAKMP SA has not formed then follow the below steps:
1) Ensure L2tp pool is properly configured and has free IP addreses available by executing the command:
#show vpdn l2tp local pool
2) Ensure RAP is defined in the RAP whitelist db  by Executing the below command
#show whitelist-db-rap
3) Ensure there are no changes done in the default-via-profile or default server group
4) If a different server is mapped in the default server group or the server group is changed to some other server group from default, then RAP would not form any entries in the ISAKMP SA and RAP will not get IP from L2tp pool.

If ISAKMP SA is formed but the entry does not have an Inner IP from L2tp pool follow the below steps:
1) Ensure L2tp pool is properly configured and has free IP addreses available by executing the command:
#show vpdn l2tp local pool
2) Ensure RAP is defined in the RAP whitelist db 
3) Also ensure that controller is running the minimum supported OS version for the RAP
4) For instance if we try to bring up a RAP3 or RAP1xx in 6.1.3.x, we would encouter this issue.