How to Force Client's DHCP Renew on Mobility Event?

[azlatkin]

Hi All,

I have a (single) client (it is a cisco IOS router) behind a wireless workgroup bridge (cisco1242).

The client's IP address is obtained via DHCP from the wired network.

Now, when roaming occurs, the Client will never have knowledge about this event,

and hence will not renew its IP address until lease expiers.

This is not a problem of course when Layer 2 roam occurs, but with Layer 3

roam it will interrupt the traffic.

The cisco's IP Mobile implementation does have this issue addressed in DCCoA

scenario: the WGB is configured to send an SNMP trap on its dotradio state change;

the cisco mobile router is configured with snmp-server manager to process this trap

and start DHCP renew on the Down/Up event. Unfortunately, this works in Mobile IP

scenario only because I cannot make it work without the mobile router registered

with a home agent.

I wonder if someone could come up with an idea on how to force DHCP renew

on a client (cisco IOS router) in such a situation - event scripting, SLA,  or ...?

alex

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[daviwatk]

You could turn "DHCP Required" on for the WLAN that the bridge is connecting to, but this may or may not address your issue depending upon how the controller learns the client address during the mobility exchange.  Maybe worth a shot.

[azlatkin]

Thank you for your comment, David, but no -- setting DHCP required on WLC will not

force a client to renew its IP; it'll simply block its traffic until the DHCPREQUEST is heard.

And it won't be heard until lease expiers.

Actually, I have found (and have successfully tested) the way to solve the task.

I did it through EEM (cisco ios event manager) configured to listen to snmp traps

sent by the wireless workgroup bridge, and to renew IP on getting VirtDotRadio "UP" event.

cheers,

alex

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[spannala6177]

Hi Alex,

If the MAR interface is dynamically changing its IP address, how will SNMP traps reach MAR-WMIC interface.

Thanks

Srikanth

[George Stefanick]

Alex,

Have you looked at static addressing (dynamic anchoring) with the new M1 code?

I blogged about it a bit ago ..

http://www.my80211.com/home/2011/5/16/wlc-configuring-dynamic-anchoring-for-clients-with-static-ip.html

Im curiuos. Let me know if this works for you ...

[azlatkin]

Yes, George, I've looked at this.

The problem with dynamic anchoring with static IP address is how

the (new) WLC detects the IP address of the client. Remember that

my client is cisco router with network(s) behind it. Snooping the

ARP request will not work since ARP timeout in IOS is 4 hours.

Orphan packet handling (I understand it is intercepting the IP

packet from client without reply(?)) will most probably give erroneous

result as this packet can be a packet from a network behind the router.

alex

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