[Dnsmasq-discuss] setting up dynamic DNS?

Simon Kelley simon at thekelleys.org.uk
Sun Sep 9 16:02:18 BST 2007

Adam Hardy wrote:
> Hi DNSmasq List
> I have a small network with a slightly different setup for the internet 
> broadband from usual. I'm having problems working out how to set up a DHCP 
> service with dnsmasq to provide workstations with permanent host names.
> Instead of the usual router providing DHCP and DNS services, I just have a 
> simple DSL modem attached to eth2 on my gateway server (isengard). Using 
> dhclient3, isengard grabs itself a public ip for eth2 via DHCP on the modem.
> isengard also runs dnsmasq on eth1 for the internal network, and I run iptables 
> as my firewall to protect it. I gave eth1 the IP
> I have 2 more linux boxes, a windows machine and a mac, and the potential for 
> other random laptops to come and go. What I want to do is set it up so that I 
> can refer to boxes by their hostname at least in linux wherever I am on the 
> network, since I do alot of ftp'ing and ssh'ing and I want to set up a samba 
> share for backups and cups for printing.
> I've reached the point where dnsmasq tells every client to use as 
> the nameserver. These clients run dhclient3 (and windows and the mac are happy too)
> But this naive approach obviously doesn't cut the mustard. Can I instruct 
> dnsmasq to be nameserver of all my hosts for each other?
> Thanks and regards
> Adam Hardy
> PS this is the hosts and resolv.conf from one client:
> adam at gondor:~$ cat /etc/hosts
>       localhost gondor.localdomain.net gondor
> adam at gondor:~$ cat /etc/resolv.conf
> search localdomain.net
> nameserver
> and /etc/dhcp3/dhclient.conf:
> send dhcp-lease-time 3600;
> supersede domain-name "localdomain.net";
> request subnet-mask, broadcast-address, time-offset, routers,
>          domain-name, domain-name-servers, host-name,
>          netbios-name-servers, netbios-scope, interface-mtu;
> send fqdn.fqdn "gondor.localdomain.net";
> send fqdn.encoded on;
> send fqdn.server-update off;
> isengard /etc/dnsmasq.conf:
> domain-needed
> bogus-priv
> filterwin2k
> dhcp-range=,,12h

All your hosts are using dnsmasq as their nameserver, so once it knows 
the hostnames associated with particular DHCP leases, everything will 
just work.

Broadly, there's two ways to do this. The first is to add names to the 
dnsmasq configuration, associating MAC addresses with names using 
dhcp-host configuration directives or in /etc/ethers. The second, and 
more common, is for the host to know its hostname, and send it to the 
DHCP server when it requests a lease: Windows (and, I'm fairly certain, 
Macs) do this always. dhclient3 needs to be told to do it with something 

send host-name "myname"

in /etc/dhcp3/dhclient.conf. Some distros are clever and configure this 
automatically: most (still) don't. Sigh.

STOP PRESS. Looking again, I see you're ahead of me, and sending the 
fqdn instead of the hostname. That should be fine, but you need to tell 
dnsmasq that "localdomain.net" is a valid network for it to accept for 
local hosts. Adding


to /etc/dnsmasq.conf will do the trick.



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