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// Other services

Port 1021: RFC3692-style Experiment 1

Port 1021 is assigned by IANA to exp1 (RFC3692-style Experiment 1).

1021

How exp1 works

Other services
client:1021exp1response client:1021exp1response

The client sends a request to port 1021 and the exp1 service answers.

Transport
TCP · UDP · SCTP · DCCP
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 1021 dangerous?

We have no specific security note for port 1021. 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 1021

ServicePortTransportDescriptionReferenceUpdated
exp1 1021 TCP, UDP, SCTP, DCCP RFC3692-style Experiment 1 1, RFC 4727, RFC 6335 -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1021, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1021'      # process listening on 1021
sudo lsof -nP -i :1021

macOS

sudo lsof -nP -i :1021

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1021 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1021
netstat -ano | findstr :1021

From another machine

nmap -p 1021 -sV <host>
sudo nmap -sU -p 1021 <host>
nc -zv <host> 1021

Block it in the firewall

sudo ufw deny 1021/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1021" -Direction Inbound -LocalPort 1021 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1021 used for?

Port 1021 is assigned by IANA to exp1 (RFC3692-style Experiment 1).

Is port 1021 TCP or UDP?

Port 1021 is registered for TCP and UDP and SCTP and DCCP.

Is it safe to open port 1021?

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 1021 is open?

On Linux run "ss -ltnup 'sport = :1021'", on macOS "lsof -nP -i :1021", and on Windows "netstat -ano | findstr :1021" to see the local process. From another machine, "nmap -p 1021 <host>" shows whether it is reachable.

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