2 dhcpd Instances on Same Platform? Take 2

Martin McCormick martin at dc.cis.okstate.edu
Wed Feb 21 20:16:01 UTC 2007


Subject: 2 dhcpd Instances on Same Platform?


	Last Fall, our organization ran DHCP failover for a while
and had to go back to a less robust non-failover mode because
some wireless net authentication devices we presently have can be
set to use only one DHCP server so traffic between the second
server and any client got lost.

	The only other problem we had was the MCLT factor since
our DHCP environment consists of a little over 8,000 static bootp
clients and almost as many, if not more, dynamic clients.  On any
given day, we have to add or delete several static bootp
addresses and the HA pair doesn't usually settle back down until
twice the MCLT value unless one gets very lucky in which case one
of the two would come right back up.  This would get things back
to full normality in 1 MCLT time period.

	I have been asked to research commercial solutions for
dhcp, some of which claim not to have this problem.  I do wonder,
however, if one could be able to run 2 instances of dhcpd from
the same platform, using two separate configurations, of course.

	One dhcpd would have not a single dynamic range defined
for it and would only contain static bootp hosts.  The second
instance of dhcpd would only have dynamic pools which would mean
that one would only need to stop and restart it when the network
configuration changed.

	We are presently running dhcpd on a remote campus that is
very small compared to our main campus and they go for weeks
without changing their static data base.  The failover has worked
flawlessly to the point that we had one dhcpd server die for some
reason and our phones never rang once.

	When we had failover running here, we also had no trouble
with it except for the amount of time it takes for both systems
to sync with each other after a kill/restart cycle.

	We are wanting to get failover back again for our
campus because we should be getting rid of the authentication
devices that kept both DHCP servers from seeing requests from the
wireless networks.

	We don't have the luxury of being able to dedicate
subnets to static bootp hosts and others to dynamic hosts.  If we
did, I wouldn't need to be asking this question.  Most of our
subnets have a DHCP range defined and everything else is static.

	Any ideas are welcome.  I have been managing our ISC DHCP
servers since 1993 and I am not looking forward to the GUI's and
various other whizzbangs that adorn many commercial products.
One can manage ISC-dhcpd from anywhere that will support command-line
communications.  That's a valuable feature in itself.

Martin McCormick WB5AGZ  Stillwater, OK 
Systems Engineer
OSU Information Technology Department Network Operations Group


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