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DHCP & HSRP both ???

If I need a redundant dhcp server on standby router, is there a possibility to configure two routers (in standby) with two dhcp servers to serve a unique segment of lan?

4 REPLIES
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Re: DHCP & HSRP both ???

I don’t understand what you are trying to describe. Can you clarify and I'll try and help?

Community Member

Re: DHCP & HSRP both ???

I think u canot have 2 DCP servers with same scope on a single segment..For router redundancy u can have HSRP for the same segment.

Community Member

Re: DHCP & HSRP both ???

There are a ton of ways you can do this..... I will go with the one I think you are trying to accomplish.

For automatic failover:

Put the DHCP Servers on the same subnet as each other and use a subnet directed broadcast IP helper statement on the DHCP Client's gateway (IP HELPER 10.10.10.255), both DHCP Servers will received the Discover packet from the cleint, both will try and answer, the client picks the server he wants to use.

For manual failover:

Just change the IP Helper to be host specific (IP HELPER 10.10.10.10)

Both scenerios are for 24bit subnetmasks.

**One thing to know about HSRP & DHCP. Just because an interface is in stanby mode doesn't mean it will not forward the DHCP broadcast. In fact, if a HSRP interface has an IP HELPER statement on it, it will always forward the packets.

Community Member

Re: DHCP & HSRP both ???

I think you'll run in to a problem keepingthe DHCP databases synced. For example, if a workstaion pulls an address lease from DHCP server 'A' for 8 hours, how does DHCP server 'B' know that the IP address is taken? If server 'A' fails, server 'B' will become the only responder and there is a high probability that the same IP address will be leased again. Unless you have a method of keeping the DHCP databases in sync. the effort involved in developing the redundancy is somewhat wasted.

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