Superscope IP Helper

Only one ip helper command per DHCP server is required.

The DHCP relay agent will insert the PRIMAY IP address of the interface that the DHCP request was recived on. So the DHCP server configuration must take this into account when configuring the scope. You might want to think about moving to a new block where you can have two contigous blocks ...

Merv,

We will be moving to a contiguous block in the future. For now I need to implement this solution to keep us going.

You said "The DHCP relay agent will insert the PRIMAY IP address of the interfacethat the DHCP request was received on".

So if the DHCP request is received on interface is 10.1.2.1 and the secondary is 10.1.6.1 any requests received from the .6 subnet will cause the DHCP relay agent to be 10.1.2.1?

If my clients can use either subnet does this matter?

Does this happen without any configuration changes to the router (no IP helper)?

Thanks for your reply.

Joel

That is correct. The relay agent will insert 10.1.2.1 into the GI address field of the DHCP request. Your DHCP server uses this info to know what DHCP scope to allocate from.

So all the magic of using the second block must be configured on your DHCP server.

probably not.

no changes given that you already have an ip helper command configured on the router interface in question.

Thanks! I'll be implementing this tonight when our office closes @

Also see the "ip dhcp smart-relay" command. The router will start using secondary addresses as the giaddr after it stops receiving replies to requests sent with the primary address as giaddr. The subnet any random host ends up in is a lottery.