Multiple IP Helper Address on a single interface

[bhatmaker]

We have two DHCP servers. I have put two IP helper address on the interface. Does the route send broadcasts to both servers at the same time? How does it determine which server to use?

[Richard Burts]

Yes if there are two helper addresses configured, the router will forward two copies of the DHCP request.

It is likely that two responses will be returned to the end station that generated the request. The router will forward both responses. It is up to the end station to choose which DHCP response to use. Typically the end station will choose the first response that it receives.

HTH

Rick

[bhatmaker]

Thanks for your insite. I did not know how the interface that sent the request to both servers would choose between them. We have some stations registering on the second IP Helper Address server instead of the first server listed.

[Richard Burts]

This is normal behavior. The DHCP will be forwarded to both servers and both servers will respond. Depending on some factors (such as load on the server) the first response may come from the first server or from the second server. The choice of which server to register with is entirely the decision of the end station and the router has no role in that.

HTH

Rick

[Kevin Dorrell]

What Rick says is correct: it sends to both servers. But to add a subtle point to the answer, if the helper addresses are unicast addresses (as opposed to directed broadcasts) it sends a unicast to each server, not broadcasts.

Kevin Dorrell

Luxembourg