Client DHCP Failure on AP410c

[GGreen]

Hello,

I have recently started having any issue on my AP410c APs relating to clients receiving a DHCP address.

When a client makes the initial connection to the AP, it sends DHCP requests for its previously held IP. Looking at packet captures, I can track these requests to the DHCP server, and the DHCP server will then sent the DHCP ACK, which I can then trace up to the wired interface that the AP is plugged into.

The client will continue sending DHCP requests, and the DHCP server will continue to send DHCP ACKs, but the client never receives the ACK. Eventually, the client gives up requesting its previous IP and will start to send DHCP Discover packets. Once again, I can follow these back to the DHCP server, and then watch the DHCP server send an Offer. Same as the ACK, the client never receives the Offer, even though I can trace the packet all the way up to the APs wired interface.

Any idea what may be going on? This issue started after upgrading the APs to version 10.7.3.0, no other significant changes have been made.

[Robert_Fredette]

This issue is very similar to one we are experiencing on much older versions of the APs.  In our case it causes the same symptoms on 3935 and 3825 APs.  In our case it was not every client on the AP but usually a small subset (4 out of 25 for instance).  There was no commonality as to who it impacted, some were fine in some locations and not in others.

While I do not have a solution to the issue we do have a workaround in place that might help you.   At the advice of GTAC we lowered the value for each impacted WLAN for the "Post-Authenticated idle timeout (seconds)" setting.  This is located in the WLAN under the Advanced button.  Lowering this setting means that the clients authentication session is cleared much sooner which fixed our issue.  In our case we were only using a PSK so reauthentication was not a big deal.

The default value is 1800 or 30 minutes.  We lowered ours to 120 or 2 minutes.  Again is is a workaround rather than a solution and we are still working with GTAC on the solution part.  Still I work at a university and with Finals approaching we were glad to have anything that worked.