Clients not getting DHCP from external server

[jonathan]

Hi,

I have a 4402 (version 7.0.235) working with 10 units of 1121 APs connected to it. The WLC is not configured to work in LAG mode. Physical portt #1 is connected to the Main Switch (trunk). I have 3 WLAN mapped to 3 Different VLAN and Everything (security and internal, external DHCP) is working swell...

Now- I have connected Physical port #2 directly to an ADSL Router (giga port), Configured Port 2 as untaggedwith the proper IP details.

I have configured this interface to receive DHCP from the ADSL Router and for some reason, Clients are not getting addresses.

When I assign a Static address to my laptop I get internet access and all is nice. I tried configuring The WLC internal DHCP server (instead of the ADSL router) and that didn't help. It seems like a DHCP problem but I dont understand the source of the problem of think of the solution.

When turning off the proxy settings I noticed that it helped. Is there anything to do with that? The problem was that after a while the other WLANs starting causing DHCP issues as well.

What is supposed to be configured? Any Expert is the House?

I attached a crappy drawing..

[Scott Fella]

Well your ADSL might not like the fact that thw WLC is proxying the dhcp request.  It's the same for an ASA.  Disabling dhcp proxy is the only way it works.  DHCP Proxy however is required if you have the WLC providing DHCP also.

Thanks,

Scott

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[jonathan]

Hi Scott,

Thanks for your answer.

So what you are basicly saying is that I have 2 choices: 1 - disable the Proxy option on the WLC and work with external DHCP servers (internal will not work when this is enabled). 2 - Enable the Proxy option and only work with the WLC internal DHCP.

I have installed many WLCs this way, having Different DHCP Servers (external and internal)  for multiple WLANs.

What do you think may be different this time? The router that I am using isn't the most expencive but it is providing DHCP to other clients (wired client) with no problems.

Thanks!!!

[Scott Fella]

Doing both works in most installs. The issue you are running into is that the external device that is doing dhcp does not want the dhcp request to be proxied.

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[George Stefanick]

Remember if you remove dhcp proxy this is a global setting. A ip helper is REQUIRED on the svi interface for all dynamic interfaces requiring dhcp services.

Also I noticed you made that interface native. Do you have other any other native vlan on the wlc like the management or is that tagged. You should only have 1 native on the wlc .

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[jonathan]

I think the system limits you to have only 1 untagged interface. In any case, the Interface that I am talking about is the only untagged interface and Why do I need IP helper if the SVI and the ADSL Router are on the same subnet (layer 2)

Thanks!! 

[Scott Fella]

The reason is that your adsl router doesn't like dhcp requests being proxied. You already determined thus by disabling dhcp proxy on the WLC.

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[George Stefanick]

No the wlc allows you to untag more than one interface, but you shouldn't.

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