IP Helper-Address

[jsalminen]

I have enabled this feature, but not yet have begun to use it. I enabled this on my fasteth 0 interface and I am also in the process of migrating this network to a new IP addressing scheme. To ensure low impact to production I set my current router IP address as SECONDARY address of the fasteth 0 interface.

Will the IP Helper-Address change the bcst address to the primary IP address of the fasteth 0 interface? If so, I do not believe my DHCP server will recognize which subnet this dhcp req packet originated from to select the appropriate DHCP IP Pool. Is this true?

[mcopelin]

Your primary address needs to be in the same subnet as your DHCP pool. Otherwise as you have indicated the DHCP server won't issue the addresses.

[mhussein · Accepted solution]

To enable DHCP relay on secondary subnets, use the global configuration command:

ip dhcp smart-relay

This will allow the router to try the all subnets during DHCP offer negotiations with the server.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_command_reference_chapter09186a00800ca694.html#1046084

HTH

Regards,

Mustafa