591 FileMaker, Inc. - HTTP Alternate (see Port 80) - System Port

591 is a System Port. Transport Protocol TCP UDP , 591 Service Name http-alt, Service Name Description: FileMaker, Inc. - HTTP Alternate (see Port 80).

Port	Protocol	Service Name	Description	Source
591	TCP UDP	http-alt	FileMaker, Inc. - HTTP Alternate (see Port 80)	IANA
591	TCP		FileMaker 6.0 (and later) Web Sharing (HTTP Alternate, also see port 80),Official	wikipedia
591	TCP UDP	http-alt	FileMaker, Inc. - HTTP Alternate (see Port 80)	bekkoame

Port	Service Name	Description
540	uucp	uucpd
1081	pvuniwien	PVUNIWIEN
1289	jwalkserver	JWalkServer
1318	krb5gatekeeper	krb5gatekeeper
2936	otpatch	OTPatch
3369	satvid-datalnk	Satellite Video Data Link
4099	dpcp	DPCP
4925		Unassigned
5417	sns-agent	SNS Agent
5717	prosharenotify	proshare conf notify

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