Access Point preferring the DHCP address over static IP configuration

[usamaaboodi]

I got cople of APs I configured them with static IP add, they are joined to the WLC fine but they got DHCP IP add, is there any idea to fix ?

thanks

[Flavio Miranda]

Hi,

 If you go to the WIRELESS Tab, then select the required AP and check it as static IP Address saving the configuration, it should remain with static IP address. This after AP has joined to the WLC.

  By configuring static IP before AP join may  the config does not survive considering the  AP will get firmware and config from WLC during the join process.

[athan1234]

Hi @Flavio Miranda 

I experienced the same issue, and in my case, it was related to FlexConnect. Just to share — there was a DHCP pool configured at Layer 3 by another provider, which was serving addresses within that range.I noticed that the access point was rebooting and obtaining an IP address via DHCP. Even if I assign a static IP to the AP, as long as there’s a DHCP server available in that subnet, the AP might still request and obtain an IP address via DHCP instead of retaining the static one. This behavior has been observed on the 9800 controller.

The first step is to perform an ARP request. However, there are two challenges: I don’t have control over the switch that handles this VLAN (it’s managed by another company), and I also don’t have access to the DHCP pool — although I’m certain a DHCP server exists for this range.

[Scott Fella]

@athan1234 What you need to understand is that if an access point has a static ip address, that works, but if the ap is not able to communicate with the controller, then the ap goes into discover mode.  That means the ap will reboot and then will try again to join a controller and if not, the ap will fall back to using dhcp.  This is something you can't control.

If you don't manage the dhcp, then allow the ap to use dhcp, that way there is no dhcp conflict from you setting up a static address and their dhcp server handing out that ip address.  Maybe this is what is happening and due to the duplicate ip address, your ap no longer can communicate with the controller and thus rebooting and going through the discovery process using dhcp.  If you don't control the dhcp scope, then you should not be using static address unless they have approved that.

[Saikat Nandy]

This is an expected behaviour in 'certain scenarios'.

By design, APs can fall back from static IP mode to DHCP mode when they are not able to associate with a controller. This helps APs to retain and new IP address from DHCP and continue to work. Also to note, the AP will retain this DHCP ip address until those are rebooted. In a network where the APs are assigned with static IPs, the DHCP IP addresses prevent the APs from being monitored. To bypass this issue, you can choose to retain the static IP addresses for APs by disabling the fallback to DHCP option.

If you are using AireOS the command is - config ap static-ip failover <enable/disable> <ap name/all>

Historically, we had issues and a bit of confusion with the way the command was designed and the how it should work. As a result a bunch of defects were also raised.. here are couple which are handy with me - 
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvs94125
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvy06837

So long story short, the behaviour is expected. However, you have option to manipulate it with command - 
If you do not want AP to failover to dhcp then 'config ap static-ip failover disable <..>'. Hope this helps.

[athan1234]

@Saikat Nandy 

Thank you for your support and for the command   'config ap static-ip failover disable — it's very inteesting.

Could you please let me know if there's any bug related to what you previously pointed out?"

AP1852E-E-K9

Primary Software Version

17.3.3.26

Predownloaded Status

N/A

Predownloaded Version

N/A

Next Retry Time

N/A

Boot Version

1.1.2.4

IOS Version

17.3.3.26

Mini IOS Version

0.0.0.0

[Saikat Nandy]

At this point there is no such bug specific to this issue as far as I can think off.

[Scott Fella]

two challenges: I don’t have control over the switch that handles this VLAN (it’s managed by another company), and I also don’t have access to the DHCP pool — although I’m certain a DHCP server exists for this range.

Why not just ask whom owns the dhcp scope to provide you with a mac reservation.  Configuring a static address in a subnet in which dhcp is enabled is not good for devices on that subnet. Also, what is wrong with getting a dhcp address, at least you will keep that address as long as your AP is connected to the network. Are you connecting a rouge AP to a network you don't own?