DNS Blacklists, DNS Monitoring and Related Links

Querying for DNS Glue Records (using dig)

On a project I’m working on, I need to establish if a domain has IPv6 glue records or not. If I had to do it on a once off, a whois lookup would answer that nicely:

$ /usr/bin/whois opensolutions.ie
nserver:     dns1.dns.opensolutions.ie 2a01:268:4::40
nserver:     dns2.dns.opensolutions.ie 2a01:268:4::41
nserver:     dns3.dns.opensolutions.ie 2a01:268:3002::61

However, in this case, I will need to do it many times on many domains and do not need to have to worry about whois servers limiting the queries or parsing the output from different whois servers.

After some digging, it looks like the nameservers of TLDs return glue records in the additional section. Let’s look by example on opensolutions.ie. First, find the TLD servers for .ie:

$ dig NS ie
ie.                     172800  IN      NS      gns1.domainregistry.ie.
ie.                     172800  IN      NS      uucp-gw-1.pa.dec.com.
ie.                     172800  IN      NS      uucp-gw-2.pa.dec.com.
ie.                     172800  IN      NS      ns3.ns.esat.net.
ie.                     172800  IN      NS      banba.domainregistry.ie.
ie.                     172800  IN      NS      ice.netsource.ie.
ie.                     172800  IN      NS      gns2.domainregistry.ie.
ie.                     172800  IN      NS      ns-ie.nic.fr.
ie.                     172800  IN      NS      b.iedr.ie.

Now query one of these for the nameservers for opensolutions.ie:

$ dig NS opensolutions.ie @banba.domainregistry.ie.
opensolutions.ie.       172800  IN      NS      dns3.dns.opensolutions.ie.
opensolutions.ie.       172800  IN      NS      dns2.dns.opensolutions.ie.
opensolutions.ie.       172800  IN      NS      dns1.dns.opensolutions.ie.

dns1.dns.opensolutions.ie. 172800 IN    A
dns1.dns.opensolutions.ie. 172800 IN    AAAA    2a01:268:4::40
dns2.dns.opensolutions.ie. 172800 IN    A
dns2.dns.opensolutions.ie. 172800 IN    AAAA    2a01:268:4::41
dns3.dns.opensolutions.ie. 172800 IN    A
dns3.dns.opensolutions.ie. 172800 IN    AAAA    2a01:268:3002::61

As you can see, the authority section contains the nameservers for opensolutions.ie which are all on the opensolutions.ie domain. We then find the glue records for these nameservers in the additional section.