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We have two DCHP servers on our 192.168.0.x LAN. One server gives out 192.168.0.100-169 and the other gives out 192.168.0.170-239.

The 2nd server only has 9 IP addresses left whereas the other has 40 left. Obviously, the 2nd server is responding faster to DHCP requests from clients.

My question is what happens when the 2nd server runs out? I assume it won't respond to DHCP client requests and therefore will let the 1st server pick up the slack?

Thanks, Rob.

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Which DHCP server software? –  Stemen Nov 16 '10 at 17:41

2 Answers 2

The second server should respond with 'can't provide', the client should then retry, the second server shouldn't respond as it already responded to that MAC very recently at which point the 1st server should respond successfully.

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Instead of having 2 DHCP servers delivering seperate ranges of IP's..

Why not have 2, delivering the same range by using failover in dhcpd?
Then its only one realm that needs to be managed...

failover peer "dhcp-failover" {
  primary; 
  address 192.168.0.1;
  port 647;
  peer address 192.168.0.2;
  peer port 847;
  max-response-delay 60;
  max-unacked-updates 10;
  load balance max seconds 3;
  mclt 3600;
  split 128;
}

I found a very simple "howto" for you too look over if your interested http://www.randombugs.com/linux/linux-isc-dhcp-server-failover-debian-ubuntu.html

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The "why not" is if it was setup that way for load balancing. If the reason you have two separate servers is because you have a massive number of DHCP requests, then you want the balancing. If you set it up how they did just because, then fail over would be pretty cool. –  Kyle__ Nov 16 '10 at 16:08
    
I cant imagine why Rob would need DHCP Load Balancing, unless he has 1000's of clients.. As far i can see, there is only 80-90 in this configuration –  Arenstar Nov 16 '10 at 16:16

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