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DHCP release from ISG


We have ISG on 7206 platform and external DHCP server. ISG relay DHCP information to this server.

When client power of PC, his session drops from ISG. But ISG don't send DHCP release to the dhcp server. IP freeing when lease time expires.

What can I do to release IP address when ISG drops the session?

Cisco Employee

DHCP release from ISG

Hi Vladimir,

In an scenario like the one described, since ISG is working as DHCP relay, the releasing of the IP address will have to be initiated by the client dy sending a DHCP release. ISG cannot do anything on it's own to trigger the release.

When the subscriber powers off the PC, does the PC DHCP client sends a DHCP release? If so, is the DHCP release relayed by ISG to the DHCP server? If the client doesn't send the release, then, as explained, I'm affraid there is not much ISG can do about it. You will have to handle that using the lease timer.

Best regards.

New Member

Hi You can still use some


You can still use some keepalive with ISG :


policy-map type service KEEP
  keepalive attempts 2 protocol ARP
policy-map type control TESTRAD
 class type control always event session-start
  5 service-policy type service name KEEP
  20 authorize aaa list ISG-AUTHOR identifier circuit-id


It's up to you to apply good keepalive parameters, but in a nutshell it does send ARP or ICMP keepalive in case of idle link. If there is no answer from client CPE, then the session is terminated.



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