WISM module and DHCP relay

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Dec 5th, 2007
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I'm in the process of testing wireless connectivity via a light weight WAP that communicates with the WISM module ( currently running However i've noticed that the wireless client doesn't pick up an IP via DHCP although the IP helper addresses, i.e. the DHCP servers are configured for the wireless VLAN. This is evidenced by not seeing a DHCP DISCOVER message in the DHCP logs for my MAC address.

From reading the config guide there is mention of the WISM acting as a DHCP relay agent, and the fact that this is tied to the virtual IP. Currently the IP is set to as per the config guide. Does this need to change? What can be done to address this issue?

Any suggestions welcome.



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sgonsalv Wed, 12/05/2007 - 21:57
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The Virtual IP being used is which doesn't appear anywhere on the network, and isn't tied to any VLAN configured on the network. So the IP is completely isolated.

From reading the config notes, it asks for a DNS gateway hostname. Here i've configured the DNS server used on the client machines.

But as explained above, the wireless client can't obtain an IP via DHCP for the Wireless VLAN

sgonsalv Wed, 12/05/2007 - 22:55
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When i manually set an IP for the clients, all IP connectivity is fine. So the only issue here is DHCP.

I've disabled the WISM from acting as a DHCP proxy, so that all DHCP info goes via the WISM untouched. But since there is no DISCOVER message seen, looks like the WISM isn't passing the SHCP info properly.

rmerritt Fri, 12/07/2007 - 19:04
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You probably know this but on your DHCP scope, have you set the advanced options for Cisco LWAPP?

pmccubbin Sat, 12/08/2007 - 05:38
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Hi Sheldon,

To add to what Ray mentioned, did you configure Option 43 on your DHCP server?

Take a look here:


If you don't have Option 43 configured on the subnet for your LWAPPs then they won't be able to receive an IP address. Your PC would be able to receive an IP but not the LWAPP.

Hope this helps and that you rate all posts which you find useful.




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