Aironet 1100 get no IP from DHCP

[n_westerberg]

When I connect an Aironet 1100 AP it doesn’t get a DHCP assigned IP adress. When connecting a PC to the same switch it gets an address from DHCP. The DHCP-server is on another subnet. I have tried with system version 12.2(13)JA4 and 12.3.2-JA. If I reset to factory default settings I get the default IP with IPSU, but when I apply DHCP the AP cannot be found with IPSU. Assigning a static IP works, but we need to use DHCP. Shouldn’t the AP at least get an IP from DHCP since the PC: s gets it? Where can the problem be?

Niclas

[dixho]

It depends. When the AP sends out a DHCP request, it is a broadcast in layer 2 and layer 3. (i.e. destination MAC address in ethernet header is ffff.ffff.fff and destination IP address is 255.255.255.255). If the AP is on a different subnet than the DHCP server, you need a router to route the DHCP server from the AP VLAN to the DHCP server VLAN

OR

the router is configured as a DHCP relay agent; so that it converts the DHCP broadcast into unicast.

Do you have a router between the two VLANs? If you do, do you configure DHCP relay agent (i.e. ip helper-address in IOS) or allow layer 3 broadcast?