Reverse-DNS

Connections to a MUSH server reveal (as part of the connection) the numeric IP address of the player's machine (or proxy).

A reverse-DNS query is initiated to turn this numeric IP address into a more human-friendly DNS name. For example, the name localhost corresponds to the numeric IPv4 address 127.0.0.1 and to the numeric IPv6 address ::1. A reverse-DNS query would then turn the '127.0.0.1' into the name 'localhost'.

Typically, these requests are made to the DNS servers which own the corresponding numeric IP range -- not to the player machine, but it is possible (particularly in a LAN environment) that the player's machine might receive these. If the player is connecting from home, the numeric IP range is typically owned by a player's ISP, and the ISP will arbitrarily assign names like pool-a-b-c-d.city.service.isp.net. If the player is connecting from a co-located box or from work, the names are usually different.

If the reverse-DNS lookup fails, and if the MUSH server is running on Windows, Windows itself will attempt to ask the player's machine for its machine name (also called a NETBIOS name) as part of trying to service the reverse-DNS lookup. The resulting name is not globally unique.

A good introduction to Reverse-DNS is available on http://en.wikipedia.org/wiki/Reverse_DNS_lookup.