DHCP Relay vs Local DHCP

leepeiwai · ‎11-23-2011

Hi,

Would DHCP client receives respond from a local DHCP server or from the DHCP server configured as IP Helper?

Cheers,

Pei

Jon Marshall · ‎11-23-2011

Pei

If for example the client was in vlan 10 and vlan 10 had a local DHCP server and an ip helper-address configured on the L3 vlan 10 interface pointing to a remote DHCP server then the client would receive a response from both DHCP servers.

Usually the client uses the first offer it gets which is likely to be the local DHCP server but it would still get an offer from the remote DHCP server so you need to make sure the 2 DHCP servers are not handing out the same IPs.

If there is a local DHCP server you generally don't use an ip helper-address on the L3 vlan interface as well.

Jon

leepeiwai · ‎11-23-2011

Thanks Jon for your quick reply!

We are migrating our local DHCP scope to another server at another site, it will be nice if we can pre config the IP helper first. I will exclude the DHCP range already allocated from the scope, at the new site. That way, 2 DHCP servers won't handout the same IPs

Cheers,

hannah