Internet-Security.com TCP port 2000 details

TCP port 2000 is the well-known port for Cisco Skinny Client Control Protocol (SCCP).
Cisco Unified Communications Manager (CUCM) and Cisco Unified IP Phones (e.g., 79xx/88xx series) use SCCP over TCP 2000 for call-control signaling and phone registration.
Cisco Unified Communications Manager Express (CME) on IOS routers also listens on TCP 2000 for SCCP endpoints.
Cisco IP Communicator (softphone) can register to CUCM using SCCP on TCP 2000.
Open-source PBXs that support SCCP—such as Asterisk with the chan_sccp (chan_sccp_b) driver and FreeSWITCH with mod_skinny—commonly use TCP 2000 to interoperate with Cisco SCCP phones.
Security note: attackers sometimes scan TCP/2000 to identify Cisco VoIP deployments, and past SCCP implementation issues have enabled denial-of-service or unauthorized phone registration in certain environments.

TCP 2000