DNS

DNS typically runs on UDP port 53, though TCP/53 is used for AXFR queries, overlarge transfers, and (since RFC 5966) pretty much anything else it wants to. Both IPv4 and IPv6 are handled by the "IN" internet record class. mDNS, based on two well-known Ethernet multicast addresses, usually runs on port 5353.

FQDNs

A fully-qualified domain name ends with a period ('.'). See "Trailing Dots in Domain Names" by Stuart Cheshire. Most DNS searchpaths have an implicit trailing '.'.