DHCP Requests Starts Failing

[scottsassin]

I have a school with 550 iPads.  We are using two 5508 WLCs sharing the number of APs.  The DHCP server and the default gateway for the network are on the firewall.  The clients are able to get a DCHP.  After some time, maybe about longer than a month, the clients are no longer able to get DCHP addresses.  A reboot of both controllers takes care of this.  Presently we are runing 7.2.110 OS.  I am going to upgrade to the latest 7.4.100, and reload tonight. 

Any insight you could give me for this effort, would be great.

[David Watkins]

Do you know the DHCP bridging mode configuration of your WLC?  Is Proxy enabled?  From the GUI.  CONTROLLER > Advanced > DHCP

If you do not have any "internal" DHCP scopes configured on the WLC, I would suggest removing the DHCP Proxy feature.  This will simply bridge your client's DHCP traffic on to the wire as is, which will hit your gateway that is acting as the DHCP server, per your description.

If DHCP Proxy is not checked, and you have your client(s) in this state, can you debug the client so we can see what's happening from the WLC's perspective?  It may require a capture on your WLC (depending on what debug reveals) to verify the bootp traffic is leaving the WLC properly.

>debug client

[gokulkrishnan]

I would like to know if you were able to find a solution to this problem. At Present I am facing a similar situation with 2 WLC 4404 running 7.0.235.2 - reboot of controllers fixes the DHCP problem for some time but again the problem arises.

Any assistance appriciated.

Regards

Gokul Krishnan

[maldehne]

disable DHCP proxy and see how it goes.

FWs may not offer any DHCP ip in case of receiving a request from relay agent.

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Please make sure to rate correct answers

[gokulkrishnan]

Thanks will try that option. Please tell me how to clear the ARP cache as it was causing last time.

[maldehne]

WLC > clear arp all

or

for specific ip

WLC>clear arp

[gokulkrishnan]

Thanks. I am gettings these arp errors

*DHCP Proxy DTL Recv Task: Sep 19 17:44:24.507: %DTL-3-ARP_CLIENT_IP_DUPLICATED: dtl_arp.c:1806 ARP entry overwrite, conflict detected via ARP Request from client with MAC-ID  ac:3c:0b:07:15:d1 and IP Address  172.18.1.156, Old client MAC-ID was 84:29:99:

*DHCP Proxy DTL Recv Task: Sep 19 17:44:23.998: %DTL-3-ARP_CLIENT_IP_DUPLICATED: dtl_arp.c:1806 ARP entry overwrite, conflict detected via ARP Request from client with MAC-ID  8c:70:5a:74:86:cc and IP Address  172.18.5.76, Old client MAC-ID was 00:23:14:7

*apfReceiveTask: Sep 19 17:44:22.794: %RRM-3-RRM_LOGMSG: rrmChanUtils.c:290 RRM LOG: Airewave Director: Could not find valid channel lists for 802.11bg

*DHCP Proxy DTL Recv Task: Sep 19 17:44:22.540: %DTL-3-ARP_CLIENT_IP_DUPLICATED: dtl_arp.c:1806 ARP entry overwrite, conflict detected via ARP Request from client with MAC-ID  ac:3c:0b:09:b6:b8 and IP Address  172.18.1.31, Old client MAC-ID was 84:29:99:1

*DHCP Proxy DTL Recv Task: Sep 19 17:44:22.534: %DTL-3-ARP_CLIENT_IP_DUPLICATED: dtl_arp.c:1806 ARP entry overwrite, conflict detected via ARP Request from client with MAC-ID  3c:e0:72:cd:19:a0 and IP Address  172.18.0.135, Old client MAC-ID was 84:29:99:

Any idea how to clear them.I have restarted Windows DHCP server

[maldehne]

check if there is another DHCP server with duplicate scope that is giving similar addresses.

[gokulkrishnan]

There is only one DHCP server but I guess it has leased out these IPs to clients - and had a different ARP entry in it's database. I am having to reconcile the windows DHCP server several times to make it consistant. Will observe for some time.

Thanks again for your continued assistance