setting a priority between redundant dhcp servers?

[Louis-David Mitterrand]

On Tue, Jun 03, 2008 at 07:50:32AM +0100, Simon Hobson wrote:
> Louis-David Mitterrand wrote:
>
>> Is there a way to set a priority between two dhcp servers operating on
>> the same LAN?
>>
>> I've noticed that my intended "secondary" answers more readily then the
>> (better spec'ed) "primary". Is there a reason why one server replies
>> faster than another identically-configured one?
>
> What other services are the servers running ? How much network traffic 
> are the handling ? Did you once run with one server only and then add the 
> second - if so, which way round ?
>
> Typically, clients will accept the first offer they receive, so all it 
> needs is a difference of probably only nanoseconds in response time to 
> deiced which response packet gets on the wire first. If one server is 
> also handling other traffic, then that will mean the DHCP packets will 
> have a slight delay before they get out.
>
> Also, if you ran one server for a while, then clients may well have  
> gained an affinity for it (they will normally try to renew with the  
> server that issued their lease). So if you "secondary" server was once 
> the only one, then clients will continue to use it in preference to the 
> newer one.

Indeed the primary is more busy than the secondary and that might
explain why the latter has become our LAN's favorite.

Thanks Simon for this detailed explanation of dhcp's inner, subtle
workings.