521 ripng - System Port | Service Name:ripng

521 is a System Port. Transport Protocol TCP UDP , 521 Service Name ripng, Service Name Description: ripng.

Port	Protocol	Service Name	Description	Source
521	TCP UDP	ripng	ripng	IANA
521	UDP		Routing Information Protocol Next Generation (RIPng),Official	wikipedia
521	TCP UDP	ripng	ripng	bekkoame

Port	Service Name	Description
749	kerberos-adm	kerberos administration
1029	solid-mux	Solid Mux Server
1984	bb	BB
1987	tr-rsrb-p1	cisco RSRB Priority 1 port
3014	broker-service	Broker Service IANA assigned this well-formed service name as a replacement for "broker_service".
3369	satvid-datalnk	Satellite Video Data Link
3756	canon-capt	Canon CAPT Port
4044	ltp	Location Tracking Protocol
4506		Unassigned
4545	worldscores	WorldScores

A port is an endpoint of communication in an operating system. While the term is also used for hardware devices, in software it is a logical construct that identifies a specific process or a type of service.

Port numbers are assigned in various ways, based on three ranges: System Ports (0-1023), User Ports (1024-49151), and the Dynamic and/or Private Ports (49152-65535);

The Well Known Ports are assigned by the IANA and on most systems can only be used by system (or root) processes or by programs executed by privileged users. Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port. The contact port is sometimes called the "well-known port". To the extent possible, these same port assignments are used with the UDP [RFC768]. The range for well-known ports managed by the IANA is 0-1023.
DYNAMIC AND/OR PRIVATE PORTS Registered Ports are those from 1024 through 49151.
The Dynamic and/or Private Ports are those from 49152 through 65535