5508 controller and changing windows dhcp server

[Stephen Rodriguez]

Under your interfaces on the WLC, did you go in and change the DHCP server to point to the new one?

HTH,
Steve

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[keithsauer507]

Hmm not on the Controller > Interfaces and each vlan.

Is this eqivalant to ip-helper like one would use on a cisco switch stack?

Think that is the problem?  If I make a change, how long is the wireless down?  A few seconds?  A few minutes?  I'd love to try it.

[Stephen Rodriguez]

when you make that change, the WLAN will blip, but it's only for a second or two.

And yes, if you have DHCP proxy enabled, and it is by default, this is like an ip helper

HTH,
Steve

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[keithsauer507]

Ok yup, Controller > Advanced > DHCP

Enable DHCP Proxy is checked.

I had my head buried in the WLAN side and also AAA side.  Because of moving from 2003 IAS to 2008 R2 NPS, I was racking my head on the new configuration with 2008 R2, the cerificates, etc...  The event log made it appear that they authenticated fine though.  Took a little longer than I wanted so I had to revert just to get people online.

Even if its a second or two blip, we may just make the change tomorrow morning and thoroughly test it before people arrive.

I didn't even think to check the lan side of the controller interfaces.  Didn't think it cared where the DHCP server was, thought it just passed traffic to the 3750 switch it has a lag group on.

Thanks for pointing this out for me.  I bet it will work when I try it. 

[Stephen Rodriguez · Accepted solution]

well if you disable proxy, than the interface 'bridges' the DHCP packet to the wire.  with proxy enabled it sends the request as a unicast to the server.

you could disable proxy as well, if you have the ip helper configured at L3.  The only time that proxy is required is if the WLC is acting as a DHCP server.

HTH,
Steve

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[keithsauer507]

Oh ok!  Thanks!

It sounds like in our configuration there's no reason for the WLC to proxy DHCP requests.  I'm more familior with ip-helper on the appropriate vlans on the 3750 switch stack that this connects to.  I'd rather manage it there to be honest.  The appropriate vlan's are already trunked over to the switch.

On the switch stack itself the WLC is connected to these ports

interface GigabitEthernet1/0/23, 25, 27, 29

description Trunk Port to Cisco WLC

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 1,5,172

switchport mode trunk

ip access-group acl1 in

channel-group 4 mode on

Example of vlans

interface Vlan1

ip address 10.1.0.254 255.255.0.0    //this is where the dhcp server lives

!

interface Vlan5

description wifi-private

ip address 10.5.1.254 255.255.0.0

ip helper-address 10.1.1.1

no ip redirects

no ip unreachables

no ip proxy-arp

!

interface Vlan172

description wifi-public

no ip address

ip helper-address 10.1.1.1

no ip redirects

no ip unreachables

no ip proxy-arp