Port 987 Unassigned - System Port

Port 987 is a System Port. Transport Protocol , Port 987 Service Name , Service Name Description: Unassigned.

Port	Protocol	Description	Source
987		Unassigned	IANA
987	TCP	Microsoft Corporation Microsoft Windows SBS SharePoint,Unofficial	wikipedia
987	TCP UDP	Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com

Port	Service Name	Description
330		Unassigned
2256	pcc-mfp	PCC MFP
2370	l3-hbmon	L3-HBMon
3128	ndl-aas	Active API Server Port
3647	splitlock-gw	Splitlock Gateway
3660	can-nds-ssl	IBM Tivoli Directory Service using SSL
5575	ora-oap	Oracle Access Protocol
5850		Unassigned
6038	x11	X Window System
6113	dayliteserver	Daylite Server

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