Can I make local Dnsmasq also resolve sub-hostnames (subdomains)?

Installing and Using OpenWrt Network and Wireless Configuration
1

Hello,

So, say I have a host dhcphostname.lan in my network, it changes it's IP address very often, the only part that won't change is it's hostname.

I can nslookup it's hostname to get it's IP. But it doesn't work if I'm trying to lookup it's subdomain, say test1.dhcphostname.lan or test2.dhcphostname.lan.

My question is, is there an option I can flip so OpenWrt knows to resolve *.dhcphostname.lan to the same IP address as dhcphostname.lan?

Thanks!

2
1 Like
3

Sorry, that wouldn't work as it requires to setup static resolves/records.

In my case, I need it to be done automatically, because it's not just one host needs to be configured. The host changes IP address, and the host comes and goes.

4

why should the host change IP?

2 Likes
5

Options:

  • Rely on mDNS or LLMNR.
  • Issue persistent IPv4 or IPv6 leases based on MAC or DUID.
  • Configure DNS with hotplug.
2 Likes
6

Thank you!

I've eventually settled down on writing a DNS proxy that transforms the query for a sub-hostname to the hostname itself before sending it back to Dnsmasq.

It goes like: Client (Sends query for xxx.host.dev.lan) -> Dnsmasq (Detects .dev.lan and forward to my proxy) -> My DNS Proxy (Sees xxx.host.dev.lan, strips xxx and dev.lan, so the domain becomes host. Then it sends host back to Dnsmasq) -> Dnsmasq (Sees host, found the result) -> My DNS Proxy (Receives the result, repack it as the result for xxx.host.dev.lan, and then reply to the previous Dnsmasq query) -> Dnsmasq (Receives the final result for xxx.host.dev.lan, reply to the client) -> Client (Receives the final result).

Yeah, I really wish Dnsmasq can add an option for this function. But now I'll just have to live without it.

Thanks again!

7 
mkdir -p /etc/hotplug.d/dhcp
cat << "EOF" > /etc/hotplug.d/dhcp/00-custom
if [ "${ACTION}" = "update" -a -z "${DNSMASQ_SUPPLIED_HOSTNAME}" ]
then exit 0
elif [ "${ACTION}" = "update" -o "${ACTION}" = "add" ]
then CMD="add"
elif [ "${ACTION}" = "remove" ]
then CMD="del"
fi
uci del_list dhcp.@dnsmasq[0].address="/${HOSTNAME}/${IPADDR}"
uci ${CMD}_list dhcp.@dnsmasq[0].address="/${HOSTNAME}/${IPADDR}"
/etc/init.d/dnsmasq reload
EOF

Updated the code to remove duplicates and looping.

3 Likes
8

Wait hold on ...

I was doing almost the same thing with no sucess. I think it's because instead of calling uci to modify /etc/config/dhcp like in your script, I was directly writing a new config file with content address="/${HOSTNAME}/${IPADDR}" to /tmp/dnsmasq.d.

Apparently your script is much clever!

I'll look a little bit deeper. Thanks a lot!

1 Like