CNAME aliases with dnsmasq
Tom Anderson
I'd like to set up a hostname alias in an office network which uses
dnsmasq for DNS and DHCP. We have a machine called server-01 (well, not
exactly, but YKWIM) which gets its address through DHCP. I would like to
arrange it so that the hostname 'cvs' (or 'cvs.ouroffice.local' in full)
refers to this machine - and that it's still findable as server-01.
Preliminary question: is there any way i can get dnsmasq to pick up
changes to dnsmasq.conf without restarting it? I believe SIGHUP doesn't do
it - the man page states:
SIGHUP does NOT re-read the configuration file.
Restarting is fairly quick, so it's not fatal if there isn't.
Main question: how do i set up an alias? From reading the man page, notes
in dnsmasq.conf, and some stuff on the web, it seems like i should just be
able to add a line like this:
cname=cvs,server-01
to my dnsmasq.conf, and it should all just work. However, it doesn't. As
far as i can tell, it has no effect at all. I've restarted dnsmasq, i've
released and re-acquired the DHCP lease on server-01 (and seen the
timestamp on the entry in dnsmasq.leases change), and i still can't see a
machine called cvs.
What am i doing wrong?
Cheers,
tom
--
COUGH UP THE BENJAMINS FOR THE CYCLE-HELMETED PIMP DADDY! -- tNToEP
Chris Davies
> I'd like to set up a hostname alias in an office network which uses
> dnsmasq for DNS and DHCP. We have a machine called server-01 (well, not
> exactly, but YKWIM) which gets its address through DHCP. I would like to
> arrange it so that the hostname 'cvs' (or 'cvs.ouroffice.local' in full)
> refers to this machine - and that it's still findable as server-01.
> cname=cvs,server-01
This looks correct, provided that dnsmasq already knows about
server-01. At least, it worked for me when I tried it on a sample setup
just now.
Chris
Tom Anderson
Thanks for trying it. Any theories on why it wouldn't work for me?
I wondered if it was because the client wasn't using dnsmasq as a DNS
server, but it sees server-01 fine, so it must be. I wondered if it was
because server-01 wasn't getting its address via DHCP, but i tried a
couple of machines, saw the entry in the lease file, etc.
It's probably time to check the logs.
tom
--
Give the future a chance!
Chris Davies
> Thanks for trying it. Any theories on why it wouldn't work for me?
Sorry, none. (I don't really use dnsmasq, here.)
Chris
Tom Anderson
Thanks anyway.
On the bright side, i have discovered what the problem was, and fixed it.
To recap, i have a line like:
cname=cvs,server-01
In my dnsmasq.conf.
Problem one was the way i was testing that the alias had been set up. I'd
been doing:
ping cvs
And occasionally:
getent hosts cvs
What i hadn't tried is:
dig @dnsmasq-server cvs
As soon as i did that, i got a hit, a very palpable hit:
;; ANSWER SECTION:
cvs. 0 IN CNAME server-01.
server-01. 0 IN A 192.168.1.86
So, dnsmasq is serving that CNAME perfectly well. The problem is with my
local resolver. Have you guessed what the problem is yet?
Something else i tried, through inaccurate copy-paste, was:
ping cvs.
And that *worked*. Now, as any fule kno, the dot at the end of a domain
name indicates that it is the end of the domain name - there are no more
name segments to come. Whereas without a dot, it's a local name, which is
interpreted relative to the current domain. Which according to my
/etc/resolv.conf:
# Generated by NetworkManager
domain tom.office
search tom.office
nameserver 192.168.1.250
is tom.office. So, when i try to get to cvs, i'm really trying to get to
cvs.tom.office.
Now, my dnsmasq.conf contains a line:
domain=tom.office
Which got sent by dnsmasq in the DHCP lease to my local machine, where
NetworkManager duly wrote it down in resolv.conf. But it seems that
dnsmasq does *not* append that suffix to cnames. That's fair, i suppose;
if i want to alias www.vatican.va to a server of my own, then adding my
domain to that would be inappropriate. I would suggest that it would be
more useful if it applied the same heuristic as name lookup, ie add the
domain if there's no dot in the name, but i imagine Mr Kelley would
disagree.
Anyway, if i change the line in dnsmasq.conf to:
cname=cvs.tom.office,server-01
Then this:
ping cvs
works. Solved!
Oh, and there was nothing of any use at all in the logs, by the way.
tom
--
But in the week its like Urbino under the wise rule of Count Federico,
only with a better football team and the nations most pleb-infested
Waitrose. And shops selling size 12 stilettos. -- Jelb, on Holloway
Tom Anderson
> To recap, i have a line like:
>
> cname=cvs,server-01
>
> In my dnsmasq.conf.
>
> [...]
>
> Now, my dnsmasq.conf contains a line:
>
> domain=tom.office
Addendum: even if i set expand-hosts, this combination doesn't create an
entry for cvs.tom.office. I have to write the domain out longhand in the
cname entry.
Chris Davies
> On the bright side, i have discovered what the problem was, and fixed it.
[excellent summary deleted]
Very good point. I'd started with the (Debian?) example dnsmasq.conf,
and chopped it to fit. This left me with four lines:
# dnsmasq -d -k -p 60053 # dig -p 60053 ...
domain-needed
expand-hosts
domain=tom.office
cname=bertand.tom.office,smartboard # smartboard is in /etc/hosts
Originally, the last line had been an unqualified name, but for some
reason that I can't fathom, cnames aren't handled with the expand-hosts
directive:
cname=bertand,smartboard # broken
Pleased to hear you've found the issue.
Regards,
Chris
fren...@gmail.com
Thanks a bunch!