The ONC RPC portmapper — ask it which port a given RPC program is on, and it tells you.
rpcbind (formerly portmap) maps ONC RPC program numbers to the ports their servers actually listen on, per RFC 1833. NFS, mountd, statd, NIS, and quota daemons register with it at startup, and clients query 111 first to find them — which is exactly what rpcinfo -p does. It is on by default on most Linux and Solaris NFS servers and answers on both TCP and UDP. Its UDP side has been abused as a DDoS reflector, and its dump reply is a free inventory of a host's RPC services.
Do not expose
An internet-facing rpcbind enumerates your RPC services to anyone and its UDP listener is a known amplification reflector. Keep it on the internal network.
$ rpcinfo -p TARGETSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.