Can configuring HSRP disrupt LWAPP Tunnel and stop DHCP?

Unanswered Question
Mar 13th, 2009
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A colleague has been moving SVI from one switch to another, including the SVI of the mgmt vlan my AP are using.

Thw whole process involved creating a new AP mgmt SVI on the 'new' switch and then modifying DHCP settings to give the AP a default gateway of the 'new' SVI.

We then waited for all AP to renew their IP and obtain the 'new' default gateway and then when all AP have moved over, we shut the SVI on the 'old' switch.

All AP mgmt was now on the new SVI on the new switch. All this happened without affecting user traffic on the wireless netowrk.

He then configured HSRP on the 'new' SVI using the original AP default gateway and then made a change to DHCP so that the AP would gradually get the new gateway when renewing their IP.

Once this had happened, the second HSRP interface was brought up.

Everything happened without affecting users, until the final HSRP interface beig brought up, when although the AP were visible from WCS, users were unable to get an IP address for any of the SSID offered.

This issue only affect AP connected back to the switch that had the HSRP work done on it and eventually it was cured by rebooting all 88 AP, although this was not ideal, as we try to be as non-disruptive as possible.

Does anyone know whether there is some form of mapping retained in the AP that would cause user vlan traffic to be trying to route back to the 'old' gateway MAC address rather than the new one?

If not...any suggestions as to what happened?

Any hints/answers/suggestions?

thank you

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dennischolmes Fri, 03/13/2009 - 04:35
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Do us a favor and keep us in the loop as to whether or not this occurs again. There were some early issues with ARP tables in the controllers. Like version 3.0 and 3.1 of the code. I would like to see if they are recurring with HSRP although I have never really ran into this before. Another issue to look at is how the dhcp request is passed to the dhcp server. The client makes the request to the AP which forwards it to the controller in the LWAPP tunnel. The controller proxies the request using the virtual interface to the dhcp server. SO, your dhcp server must support dhcp by proxy and all routes there must be stable. This could be causing you a problem. If it is, try the cli command "config dhcp proxy disable" as this might solve that particular problem.


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