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New Member

WLC2106 DHCP problem.

Hi, all

I have a problem with DHCP IP distrbution.

My wireless environment is WLC2106 + 6 LAPs(1131AG).

The symptom is that WLC sometimes distributes duplicated IP addresses to clients, so WLC have wrong ARP tables.

Eventually, some clients which have duplicated IP addresses can't communicate with WLC and others as well.

Does anybody know how to solve this problem? (I think it's one of WLC bugs)

If so, please let me know.

Oh, I also have a log message relevant to this problem.

I attache the log message below

firmware version "[WARNING] dtl_arp.c 1656: Unable to delete ARP mapping."

firmware version "%DTL-4-ARPMAP_DEL_FAILED: dtl_arp.c:1818 00:40:ffffff96:ffffffae:38:fffffffe Unable to delete ARP mappingIP belongs to 00:40:96:ae:49:18"

P.S : all of my clients use Cisco wireless interface card(CB21AB) and also use ADU(Aironet Desktop Utility).

I use only internal WCL DHCP server on this subnet, so there is nothing to affect it working wrong.


Hall of Fame Super Gold

Re: WLC2106 DHCP problem.

Are you sure you don't have two (or more) DHCP servers dishing out the same IP Subnet range?

Disable the DHCP details from your WLC and see if duplicate IP Address is still ongoing.

New Member

Re: WLC2106 DHCP problem.

I'm sure that I don't have any DHCP server on the WCL subnet expect for WLC internal DHCP server.

When this problem happend, I rebooted all my wireless devices(WLC, 6APs) while client already associated to APs.

When the devices perfectly came up, I found that some clients have duplicate IP address. so I removed the wireless interface card which belong to duplicate ip client and insert it again.

from that piont, the client got a new IP again from WLC DHCP server.

I assume that ADU(Aironet Desktop Utility) have some special mechanism like retaining IP address for ramdom time

If this kind of the mechanism exsist, this problem makes sence because when WCL finish a rebooting process and it comes up, All WLC DHCP table(such as lease time table) is cleared.

So it could be possible WLC gives clients duplicate IP Because the WLC doesn't have any infomation about which IPs are already given.

What do you think about it?

Hall of Fame Super Gold

Re: WLC2106 DHCP problem.

I'm using CB21AB card and I don't experience this problem.

New Member

Re: WLC2106 DHCP problem.

you also use ADU ?

Hall of Fame Super Gold

Re: WLC2106 DHCP problem.

Yes. I am also using ADU v4.4.

Re: WLC2106 DHCP problem.

Im curious what is your lease times?

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
New Member

Re: WLC2106 DHCP problem.

Lease time is default value 24hours.


It's really hard to find the cause.

Cisco Employee

Re: WLC2106 DHCP problem.

After a quick look it looks like this is a known issue with the internal DHCP server. After a WLC reboot, the internal server clears it's lease history which may result in duplicates being given out.

So, I would say either use an external DHCP server, or open a TAC case.

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