853 Unassigned - System Port

853 is a System Port. Transport Protocol , 853 Service Name , Service Name Description: Unassigned.

Port	Protocol	Service Name	Description	Source
853			Unassigned	IANA
853	TCP UDP		Mac OS X RPC-based services, Used by NetInfo, for example	Apple.com

Port	Service Name	Description
1068	instl-bootc	Installation Bootstrap Proto. Cli. IANA assigned this well-formed service name as a replacement for "instl_bootc".
1132	kvm-via-ip	KVM-via-IP Management Service
2138	unbind-cluster	UNBIND-CLUSTER
3176	ars-master	ARS Master
4698		Unassigned
5514		Unassigned
6503	boks-clntd	BoKS Clntd IANA assigned this well-formed service name as a replacement for "boks_clntd".
7911		Unassigned
8345		Unassigned
9647		Unassigned

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