11-06-2020 06:38 AM - edited 07-05-2021 12:45 PM
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
11-09-2020 08:55 AM
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!
11-11-2020 10:21 PM
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:
We are confused
11-12-2020 07:05 AM
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
11-11-2020 06:45 AM
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.
11-11-2020 10:24 PM
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
11-12-2020 06:47 AM
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