[Dnsmasq-discuss] Secondary/tertiary dns servers in dhcp offers?

[Al Hooton]

	Simon,

	Thank you for a very helpful response...

On Fri, 2004-11-12 at 20:50 +0000, Simon Kelley wrote:
> >
> So
> 
> dhcp-option=6,0.0.0.0,1.2.3.4,5.6.7.8
> 
> will use dnsmasq as the first nameserver, and the last two as backups.

	OK, I see, thanks!
> 
> Getting the backup servers from /etc/resolv.conf directly is not possible.
> 
> You should think fairly hard before doing this. Don't forget that the 
> upstream nameservers will not know about any names which dnsmasq is 
> getting from /etc/hosts or the DHCP system, so a query for those names 
> which gets sent direct to an upstream nameserver will fail mysteriously. 
> Worse, I don't think that the DHCP spec actually specifies that the DNS 
> servers are in priority order, so you might come across a client which 
> uses a different order and therefore has problems.

	Hmmm, this is a very good point.  OK, so it probably makes more sense
for me to have a backup/secondary dnsmasq machine on my local network to
deal with the times the primary is offline.  This brings up a few
questions:

dns replication #1
Can I get two (or more) dnsmasq machines to let each other know about
new A records they cache (including those spawned from dhcp leases), so
if the primary goes down I have a secondary that can take requests?  I
believe the "server=/domain/ip-addr" directive may do this, but I'm not
sure from the config file comments.

dns replication #2
I'm comfortable having an authoritative dns server on my local net
(behind a firewall that blocks incoming dns requests from the outside
anyway).  It seems that the best way to have a "primary" dnsmasq
machine, and a "secondary" dnsmasq machine would be to make the primary
one authoritative, yes?

dhcp secondary
I'm not sure how I would have a "secondary" dhcp server, that could pick
up if, and only if, the primary one were offline.  If I run dnsmasq on a
second machine on my local net, I would like to have it be both a backup
dns server and dhcp server, even though I know the leases would not be
shared between the machines (or is there a way to do that with
dnsmasq?).  I understand the problems that might cause, but I'm willing
to deal with them for the few times it might arise on my small net.


	Questions, questions...    8^)=   Thanks again for your assistance!

Regards,
Al