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In what circumstances should you configure multiple DHCP servers on the same subnet?

My understanding of using more than one DHCP server is that your clients will use the nearest DHCP which could be unpredictable.

However I have read a suggestion of using 2 dhcp servers where one provides 80% of the addresses and the other 20% but I don't see what the advantages of doing this.

Simon Foster
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  • The clients don't use the "nearest", they use whichever responds first. And 2012 makes big improvements here in terms of HA and the whole 80/20 old idea: http://blogs.technet.com/b/teamdhcp/archive/2012/06/28/ensuring-high-availability-of-dhcp-using-windows-server-2012-dhcp-failover.aspx – TheCleaner Mar 03 '14 at 17:07
  • `My understanding of using more than one DHCP server is that your clients will use the nearest DHCP which could be unpredictable` - Unpredictable how? – joeqwerty Mar 03 '14 at 17:08

2 Answers2

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In what circumstances should you configure multiple DHCP servers on the same subnet?

You want more than crappy uptime.

My understanding of using more than one DHCP server is that your clients will use the nearest DHCP which could be unpredictable.

This is probably why DHCP in Windows has the ability to work in a failover scenario with synchronized access? You can couple 2 servers (more exactl: address areas) and have them synchronize between two servers, which nicely means you have none of the issues you seem to have ;)

but I don't see what the advantages of doing this.

Uptime. Maybe in your world hardware never fails, in mine it does. Pretty crappy when the only DHCP server fails, especialyl with IPv4 where machienes will not pick up a IP when the server goes back online. HAve fun getting everyone to restart his machine in a larger company. Note that with IPv6 that changes as machines get dynamic notifications when the assigned networks change.

TomTom
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The configuration you're talking about is known as "split-scope," and the advantage it provides is redundancy - if one DHCP server goes down, the other can take over, instead of having your clients simply unable to receive a DHCP address. Of course, the reundancy comes with a management overhead, but it can be worthwhile.

And since you're doing Windows, it might be worthwhile to look into the failover and hot-standy DHCP modes, with offer the redundancy of split-scope, without the drawbacks (for the most part).

HopelessN00b
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