Why a DNS server on an ATA?

Question

I was portscanning this home network from the outside and found three open ports: telnet(!), http and domain. I quickly realized that those ports were belonging to an Eltek R7121-L1 ATA that is connected before the router. Http and telnet are obviously for administration, but what is the DNS-server used for?

Answer 1

When I looked up the specs of this device they say it supports DNS SRV under RFC:2782. You can find the specs here

You can find additional information about DNS SRV at RFC2782. Here is some good information using DNS SRV with a SIP implementation: