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DHCP failover/hot standby

Posted on 2016-08-03
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Last Modified: 2016-10-08
I'm configuring another DHCP server 2012r2 as a Standby server in case my primary DHCP server fails. On my CISCO routers, I have the IP helper pointing to my primary DHCP server. Will I need to add another IP helper address to all my routers pointing to the failover DHCP server in the case my primary goes down? Or will it just sense there is no heartbeat on the primary DHCP server and start pulling from the Failover DHCP server? Please advise... Thx!
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Question by:idocinfo
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Schnell Solutions earned 500 total points
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Hello.

Like you stated at first, if you are adding an standby DHCP server you need to add the RFC 1542 (called IPHELPER for Cisco) in all your networks, therefore your routers or L3 switches. Therefore, at the end both IPs are going to be added in your routers, and anyone of your DHCP servers will responds the DHCP requests received.
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by:Schnell Solutions
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By the way, when you add two IPs to the IPHelper, the request that the router receives is forwarded to each IP Added. It means that both DHCP servers will receive the request, but just the active one is going to answer the request (Assuming that it is an Active/Passive scenario).

If you are using an Active/Active scenario the request is received by both servers, then both servers will answer back to the router, but the client will receive the answer that arrives first, and the second one will be discarded.
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by:idocinfo
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Perfect...thank you!
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by:Schnell Solutions
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You are welcome.
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