Constant DHCP Discover/Offer for all wireless clients

[fgasimzade]

Hello,

We have noticed a high CPU/Memory usage for both vWLC version 8.1.111.0 and our MS DHCP Server

vWLC is configured with DHCP Proxy

When sniffing the traffic on DHCP server I noticed that WLC's Wireless Interfaces are constantly sending DHCP Discover for clients even if they already got IP address from DHCP.

So it looks like this:

DHCP Discover from WLC

DHCP Offer from DHCP

DHCP Request from WLC

DHCP ACK from WLC

And then the proccess starts over again for the same client (MAC) with Discover(WLC) - Offer(DHCP) messages. Sometimes I notice DHCP NAK messages for the client, which previously received an IP

Lease time is set to 1 hour.

This doesnt happen to wired clients.

MS DHCP server is clustered with another MS DHCP server acting as a secondary.

Do you have any thoughts on this?

Thank you

[patoberli]

You are running such an incredibly old version of WLC, I don't even think it's worth to troubleshoot this. Please first upgrade to the latest 8.2, or if your AP supports it, 8.5. Please note the upgrade paths in the release notes!

[fgasimzade]

Hello,

Thank you for your reply. We considered this option, but seems like there is no direct upgrade from 8.1 to 8.2 and 8.3 - the upgrade failed.

There is even no 8.1 in the release notes here:

https://www.cisco.com/c/en/us/support/wireless/wireless-lan-controller-software/products-release-notes-list.html

We are confused

[Grendizer]

8.1 is not included in that page because it is deferred, not recommended, end of life release, you can upgrade directly from 8.0 and 8.1 and 8.2 to 8.3, if your APs can handle 8.5 then it is the recommended release for older WLCs like 5508, 2504, 8510 if you have newer WLCs like 3504, 5520, 8540 then the recommended release is 8.10

All details in here: https://www.cisco.com/c/en/us/support/docs/wireless/wireless-lan-controller-software/200046-tac-recommended-aireos.html#anc16

[Grendizer]

as Patoberli said, you need to upgrade, but it’s worth to disable DHCP proxy from the WLC and configure the connected switch with ip helper command, and it’s good to extend the DHCP release time because 1 hour means the clients will have to check the ip address every 30 minutes (50% of the lease time) with the DHCP server and that’s unnecessary traffic/load unless you have to.

[fgasimzade]

Thank you for your reply. When we disable DHCP proxy we start seeing DHCP flooding all over the network, like a storm (some switches even timeout on pings)

I did increased the lease time, thank you

[Grendizer]

Yes, you need to disable that from the WLC and enable it from the connected switch so the switch will take that DHCP broadcast and unicast it to the DHCP server. With Cisco switches the config is ip helper-address x.x.x.x and if you have other switch vendor I'm sure they have similar command to enable that.