APs fallback to DHCP

[PetriSignal]

Hi,

all our APs are with static IPs. Now and then APs fallback to DHCP mode and I can't figure out why. Can I disable the IP fallback feature?

Regards,

Petri

[Stephen Rodriguez · Accepted solution]

no this can't be disabled. This feature is in place to keep the wireless network up and running. If an AP can't communicate with the static address that it has, it falls back to using DHCP to try and communicate.

IMHO, you are better served with having the AP be dhcp vs. static, as the AP is managed via the WLC instead of individually

Sent from Cisco Technical Support iPad App

[PetriSignal]

Okay, thank you for the quick reply.

-Petri

[jason crockett]

While I get Cisco's logic behind this feature I don't agree that we are better served with the APs being DHCP vs Static. This feature causes issues with monitoring. You can't successfully monitor the APs with a 3rd party application if you are using a DHCP address since the IP would change frequently. Further complicating the issue is the controller based APs don't use SNMP so you can't base the monitoring off of the DNS name.

[Rich R]

@jason crockett The whole point of controller based wireless networks is that all your configuration and monitoring is done at and from the controller so you're coming at this from completely the wrong approach - you shouldn't be trying to monitor the AP directly - that is literally the cause of your problem.  Why would Cisco change the whole design concept because you've chosen an inferior monitoring product that isn't able to monitor AP status from the WLC like all the reputable tools do?  It works just fine that way for thousands of other customers, not only of Cisco kit, but also other vendors' controllers too.

The AP falls back to DHCP when it loses connectivity to the WLC so maybe you should be looking at the root cause of the loss of connectivity rather than complaining at Cisco for their APs working as designed.  The vast majority of us use DHCP with option 43 which makes installing and managing the APs so much easier.

[jason crockett]

Hey Rich. Like the vast majority, we also use DHCP with option 43 when we initially add a new site to our Cisco controllers. Once the APs have joined via DHCP they are statically assigned an IP address. Our "inferior" monitoring product works as intended. It monitors up/down based off an IP address and SNMP. Or in some cases, ICMP only. We are a large enterprise and our Service Desk is responsible for monitoring tens of thousands of nodes. We prefer that they can monitor all systems from a centralized monitoring system. Imagine the complexity created if we asked them to monitor each system we deployed from that exact application rather than a centralized monitoring system.

As I mentioned, I understand the logic behind this feature and that it's required so that the AP can continue to try to communicate. But, once it has re-established communication it should be able to roll back to the static IP without manual intervention. 

We also know the root cause of this issue is that some of our links can become congested, causing round trip times between the AP and controller to exceed 300ms. 

Maybe instead of complaining that every customer of Cisco should use the Cisco application for monitoring you should understand that not every enterprise is the same.

[Rich R]

> "every customer of Cisco should use the Cisco application for monitoring"
@jason crockett did I ever say that? 
There are 3rd party applications capable of monitoring AP status via WLC and we in fact use one such system (not from Cisco) to monitor in excess of 23,000 APs across 20 WLCs (as well as all the other routers, switches etc in the network).  All those APs use DHCP with option 43.

I also specifically mentioned other vendors which use the same architecture so this is not unique to Cisco in any way.

If you want Cisco to change the way their APs work you can raise an enhancement request through your Cisco SE and account team.  Cisco will usually only progress that type of enhancement with a suitable business case and/or if enough big customers are asking for it.

[Infra AM Network]

Hey Jason,

How do you roll back to your static IP from the Fallback IP? 

[chris.thomas]

The labor intensive work around I have to use is change the switch port from trunk mode to access mode with "switchport access vlan X", where X is appropriate management vlan.  Then shut/no shut the port.  Then wait for the AP to register with static address.  Then change port back to trunk mode after the AP registers with static address.