Dnsmasq

For some application, it is useful to have a DNS server running locally on your maching. I use dnsmasq for this. However, ubuntu configures dnsmasq for use on a gateway per default, which is not what I want it for. I want the following things changed:

• dnsmasq should use as upstream DNS server whatever resolvoncf resp. dhclient determine to be my DNS server.
• all my local programs should however ask only dnsmasq to resolve names.
• dnsmasq shall work locally only, not act as a DNS server for others in the network
• dnsmasq shall not act as a DHCP server.

So, here's the setup for /etc/dnsmasq.conf:

# Never forward plain names (without a dot or domain part)
domain-needed
# Never forward addresses in the non-routed address spaces.
bogus-priv
 
# use the resolv.conf generated by resolvoncf for upstream resolution.
# /etc/resolv.conf will initially be a symlink to that file. we will change that later, see below.
resolv-file=/etc/resolvconf/run/resolv.conf

# try upstream servers strictly in order
# useful if you want to override the upsteam DNS server you get from DHCP in the resolvconf config.
strict-order

# only work locally
interface=lo
listen-address=127.0.0.1

# NOTE: the bind-interfaces is rejected by dnsmasq on my machione, even though it's present in the example config. odd.
# but the restrictions above should be sufficient anyway.
# bind-interfaces=lo

# no DHCP (since we only listen to loopback, we only need to exclude loopback)
no-dhcp-interface=lo

If you have a stupid ISP that uses wildcard A records to grab requests for unknown domains, you can filter them out like this:

# filter bogus A records
bogus-nxdomain=62.157.140.133
bogus-nxdomain=80.156.86.78

If you want to serve SRV records for special services (in this case, Jabber multi user chat):

# The fields are <name>,<target>,<port>,<priority>,<weight>
srv-host=_xmpp-server._tcp.conference.yourbox,yourbox,5269

Then restart dnsmasq:

> sudo /etc/init.d/dnsmasq restart

Now we only have to tell all programs on the local system to use dnsmasq to resolve domains. The DNS server used to resolve domains is configured in /etc/resolv.conf, which resolvonf turns into a symlink to the file it generates, which (on ubuntu) is /etc/resolvconf/run/resolv.conf. Since we want dnsmasq to act as an intermediarry, we remove the symlink and replace it by a file containg a single nameserver entry:

# check that /etc/resolv.conf actually is a symlink
> ls -l /etc/resolv.conf
lrwxrwxrwx 1 root root 31 2009-02-11 22:37 /etc/resolv.conf -> /etc/resolvconf/run/resolv.conf

# if so, remove it, then create a fresh one:
> sudo rm /etc/resolv.conf
> sudo vim /etc/resolv.conf

The new file should contain the following:

# NOTE: dnsmasq is running on this system. It uses the upstream servers defined in
# /etc/resolvconf/run/resolv.conf wich is automatically (re-)generated by resolvconf.
# For temporary overrides, edit /etc/resolvconf/run/resolv.conf
# For permanent overrides, edit /etc/resolvconf/resolv.conf.d/head

nameserver 127.0.0.1

Don't forget to make it readable by all:

> sudo chmod 644 /etc/resolv.conf

now, try it out by typing:

> host loclhost
localhost has address 127.0.0.1

This should work for any hostname you specify in /etc/hosts. If you get no response, or some other address, somethign went wrong.

Note that resolvconf will complain if /etc/resolv.conf is no longer a symlink. According to the man page, this can be fixed by adding to following to /etc/default/resolvconf:

REPORT_ABSENT_SYMLINK=no

However, this doesn't work for me. resolvconf still complains.