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// Other services

Port 121: Encore Expedited Remote Pro.Call

Port 121 is assigned by IANA to erpc (Encore Expedited Remote Pro.Call).

121

How erpc works

Other services
client:121erpcresponse client:121erpcresponse

The client sends a request to port 121 and the erpc service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Well-known (0-1023)
Category
Other services
01 Security

Is port 121 dangerous?

We have no specific security note for port 121. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 121

ServicePortTransportDescriptionReferenceUpdated
erpc 121 TCP, UDP Encore Expedited Remote Pro.Call - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 121, and is it reachable?

Linux

sudo ss -ltnup 'sport = :121'      # process listening on 121
sudo lsof -nP -i :121

macOS

sudo lsof -nP -i :121

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 121 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 121
netstat -ano | findstr :121

From another machine

nmap -p 121 -sV <host>
sudo nmap -sU -p 121 <host>
nc -zv <host> 121

Block it in the firewall

sudo ufw deny 121/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 121" -Direction Inbound -LocalPort 121 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 121 used for?

Port 121 is assigned by IANA to erpc (Encore Expedited Remote Pro.Call).

Is port 121 TCP or UDP?

Port 121 is registered for TCP and UDP.

Is it safe to open port 121?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Close the port if nothing on the host needs it.

How do I check if port 121 is open?

On Linux run "ss -ltnup 'sport = :121'", on macOS "lsof -nP -i :121", and on Windows "netstat -ano | findstr :121" to see the local process. From another machine, "nmap -p 121 <host>" shows whether it is reachable.

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