Muliple servers

Simon Hobson dhcp1 at
Tue May 6 08:46:40 UTC 2008

Eustace, Glen wrote:

>We currently have 4 DHCP servers, 1 at each site + a 2nd at the main 
>site.  Each site peers with the second server at the main site. 
>This provides 2 servers for each network.
>In terms of increasing availablilty, is there anyway of having 
>multiple peers ? If not, which I believe is the case, what is 
>considered to be best practice for improving availability ? 
>Clustering ? sub-dividing sites into more zones each with their own 
>servers ?
>Any comments appreciated.

I think you have about the optimum setup there. You can only have two 
peers in a failover relationship, so it's not really practical to add 
additional servers. To completely lose DHCP service then you'd have 
to lose both a site-local server AND the WAN link - at which point 
you probably more to worry about than just the DHCP.

As long as you have reasonably reliable servers, and a reasonably 
reliable network, then I personally wouldn't be too concerned.

Of course, the other factor is having plans (as part of your business 
continuity process) so you know what to do if you do have a failure - 
that is far better than lots of redundant servers etc and everyone 
running round like headless chickens when a failure still happens ;-)

You could have a 'warm spare' DHCP server fairly easily - just 
configure it ready to take over from a live server but with an empty 
leases file. Should a server fail, then shut it down and start up 
it's replacement, then wait while it copies the leases database over 
from the peer. You'll obviously need a WAN link for this to work, but 
IMHO a backup (even a 64k ISDN channel or VPN over ADSL) is so easy 
and cheap to have that if you are talking about increasing 
availability from what you have then you'll already have a redundant 
network anyway.

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