Cisco High Availability and Internal DHCP Server Service with WLC Code 7.4.121.0

I have been implementing High Availability on Cisco 5508 Controllers. The deployment has been going well. However, some remote hospitals have a pair of 5508s that are serving up the DHCP Scope for their Guest Networks. I didn’t realize this was a problem until I attempted the implementation of the HA. The site in this example is called Site. It has two 5508 Wireless Controllers (WLC) that have 250 AP Licenses each. I had planned on decommissioning WLC2 so that it could be re-purposed at another site to replace the aging Cisco 4400 Wireless Controllers.  The redundancy plan would move from N+1 to HA. The HA unit is a special unit from Cisco that has to be paired to a WLC with active AP licenses. The HA unit, by itself can’t command and control Wireless Access Points until its paired unit is unavailable.

I implemented HA. During the HA procedure it will tell you that you have to disable your DHCP Scope. !Reference Needed

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Shows the status of the WLC HA. You can see it is in Active State and is the Primary Unit of the HA Pair (wlc1). The Secondary Unit is in Standby Hot State (wlc1-ha). Everything is running good. But we can see that the DHCP Scope is not enabled.

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Lets try to enable the Guest Network DHCP Scope.

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This doesn’t look good. Lets break the HA Pair so we can get the site back to its N+1 Redundancy.

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One of the problems, I ran into at this point was that I was reverting this work remotely. The Site is 1 hour drive away. When I rebooted the unit to disable the SSO (HA) mode, the wlc-ha unit thought that the wlc1 unit had failed. The wlc1-ha unit transitioned to the Active Unit. You will not have the ability to connect to wlc1 since the wlc1-ha has taken control of the Management IP Address.

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Notice the Unit is = to the Secondary – HA SKU. This is wlc1-ha.

So lets see what happens when we attempt to regain connectivity to the wlc1, by shutting the up links to the wlc-ha down.

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This is not looking good.

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Still not looking good. Luckily, I have a contact onsite who flipped the power switch for me. The wlc1-ha ports are still admin shut. So after the reboot of the wlc1 unit, I should regain connectivity.

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As you can see, I did regain connectivity and I was able to then proceed to enabling the DHCP Scope.

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Now both units wlc1 and wlc2 are functioning in N+1 redundancy. The wlc1-ha unit is waiting for its uplinks to be re-enabled. But first I have to figure out where to move the DHCP Server Services to.

I contacted Cisco and was informed that the DHCP Server Services will not work until 8.0 code release. In 8.0 code, the DHCP Database is synchronized across the HA pair. So the next step is to test this on 8.0 WLC code in my home lab.

Cisco….

Please be informed that the internal DHCP server does not function while using HA. Here is a document on HA :

http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-5/High_Availability_DG.html


Todd Smith
Wireless Network Engineer


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