config help - scaling problem

David W. Hankins dhankins at
Thu Mar 4 23:30:40 UTC 2010

On Tue, Mar 02, 2010 at 09:40:17AM -0600, Marc Perea wrote:
> Since all of our environment comes from the .conf and not the .leases,
> does anyone see any reason why we shouldn't have 1 or more other servers
> also performing active dhcp servicing (as was recommended)? If I were to
> point my relays to several DHCP servers, it seems I'd have more
> redundancy and failover without having to use any protocol, which is a
> benefit in my mind. Any flaws in that thinking?

Make sure the servers don't serve overlapping address space.  They
can get into a nasty infinite loop packet storm situation otherwise.
Just put half the address space on each system and that should be fine
(but it doesn't exactly win you true redundancy).

> We try to keep up to date on the software, but also don't upgrade
> from a stable release unless there's something in the patch notes of
> worth to us - as such we're currently on 3.1.1. It appeared to me
> that the major difference between selecting 3.1.0 and 4.x was whether
> or not we wanted IPv6 support.

4.0.x is just where we added DHCPv6 support.  I appreciate to do that
we touched a lot of code, and that makes for some timidity in upgrading
to a 4.* release, but we actually touched more code more invasively in
4.2 than we did in 4.0 (3.1 had a lot of the option cache changes we
needed for DHCPv6 that are common code to DHCPv4 and DHCPv6, as
preparation for the DHCPv6 work - we only had to rework them a little
for 4.0 while mainly writing the body of new code for DHCPv6 protocol

DHCP 3 is the past, DHCP 4 is the present, and DHCP in BIND 10 is the

The further you are in the past, the harder it is for us to tell you
what you're going to experience.  Unfortunately, no one gets to live
in the future.

But I do get postcards sometimes.

> in environments like mine. It sounds like I would like to use both the
> delayed fsync() and host option matching - is there a release that
> supports both of these?

Not currently, we still need to put delayed-fsync back in 4.2.0.  I
hope to have it in 4.2.0b1.  At the same time I doubt in your scenario
that you would use both at once (delayed-fsync works with dynamic
leases, those "range" statements, host records with fixed-address
statements are entirely stateless by design).

Did you know ISC provides support contracts for DHCP?
Support ISC and we'll support you.
David W. Hankins	BIND 10 needs more DHCP voices.
Software Engineer		There just aren't enough in our heads.
Internet Systems Consortium, Inc.
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