DHCP Relay

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Dec 29th, 2008
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I just want to know how ip helper-address work when we have multiple DHCP server for redundancy.

If we configure ip helper-address command twice with two different DHCP server, How does it going to relay the DHCP request message ? I appreciate if any one could explain me.


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Richard Burts Mon, 12/29/2008 - 20:52
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The behavior of ip helper-address is quite simple and straightforward. When the Cisco router configured with two ip helper-address received an eligible local broadcast (such as DHCP) it will forward a copy of the broadcast to each of the configured helper addresses. The result is that each server will receive a copy of the request. Note that this is exactly the same effect as if both servers were in the local LAN where they would both receive the DHCP request.

Part of what this means is that while you can easily have redundant servers it is difficult to have primary and backup servers.




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