DNS server

tcp        0      0 0.0.0.0:53              0.0.0.0:*               LISTEN
udp        0      0 127.0.0.1:53            0.0.0.0:*                      
udp        0      0 209.217.69.50:53        0.0.0.0:*                         
udp        0      0 130.47.10.251:53        0.0.0.0:*                          
udp        0      0 0.0.0.0:53              0.0.0.0:*

The DNS server opens a UDP port for each network interface. It also listens for requests over TCP connections. TCP connections are only used if the response will not fit into a single, unfragmented UDP packet. See section 7.7