ip helper statement for 7921 phones when DHCP is on the router

Rick Morris · ‎01-21-2009

I need to set-up a ip helpet statement in my WLC so the 7921 phones grab an IP address. The DHCP scope is on the router.

Where do I point the helper statement to?

sschmidt · ‎01-22-2009

Wherever you place the helper address it needs to point to the end point that is performing DHCP. The idea of the helper is to take a broadcast DHCP discover and unicast it to the destination because the routers in between do not forward broadcasts by default.

Rick Morris · ‎01-22-2009

If DHCP is on the router what do I point the helper statement to?

See config below...

ip dhcp pool VLAN60

network 10.125.60.0 255.255.252.0

dns-server 10.1.0.121 10.2.0.122

default-router 10.125.60.1

domain-name lzb.hq

option 150 ip 10.251.125.1

sschmidt · ‎01-22-2009

The helper address needs to be the address of the router interface that connects to or has a path to where the DHCP DISCOVER originates.

migilles · ‎01-26-2009

You only need an IP helper on a L3 interface if the DHCP server is not in that network.

http://www.cisco.com/en/US/docs/ios/12_3t/ip_addr/command/reference/ip1_i1gt.html#wp1169356

Other than that in the interface setup on the WLC, will have to configure the DHCP server addresses as the WLC serve as DHCP proxy.