Internet-Security.com TCP port 2023 details

Reverse Telnet on console/terminal servers commonly uses TCP 2001–20xx; on Cisco IOS access servers (e.g., 2511 or 2600/3600 with NM-16A/32A), async line 23 is accessed via TCP 2023 using the Telnet protocol.
Digi PortServer TS/CM serial console servers likewise map serial port n to TCP 2000+n for Telnet or raw TCP; thus their port 23 is typically reachable on TCP 2023.
Some other console-server platforms can be configured similarly (e.g., Opengear), making TCP 2023 a per-port Telnet endpoint for the 23rd attached device.
Security note: when exposed to the internet, TCP 2023 is sometimes probed/brute-forced as an alternative Telnet entry point to reach device consoles.

TCP 2023