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// Other services

Port 3303: OP Session Client

Port 3303 is assigned by IANA to opsession-clnt (OP Session Client).

3303

How opsession-clnt works

Other services
client:3303opsession-clntresponse client:3303opsession-clntresponse

The client sends a request to port 3303 and the opsession-clnt 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
Registered (1024-49151)
Category
Other services
01 Security

Is port 3303 dangerous?

We have no specific security note for port 3303. 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 3303

ServicePortTransportDescriptionReferenceUpdated
opsession-clnt 3303 TCP, UDP OP Session Client - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 3303, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3303'      # process listening on 3303
sudo lsof -nP -i :3303

macOS

sudo lsof -nP -i :3303

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3303 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3303
netstat -ano | findstr :3303

From another machine

nmap -p 3303 -sV <host>
sudo nmap -sU -p 3303 <host>
nc -zv <host> 3303

Block it in the firewall

sudo ufw deny 3303/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3303" -Direction Inbound -LocalPort 3303 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3303 used for?

Port 3303 is assigned by IANA to opsession-clnt (OP Session Client).

Is port 3303 TCP or UDP?

Port 3303 is registered for TCP and UDP.

Is it safe to open port 3303?

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 3303 is open?

On Linux run "ss -ltnup 'sport = :3303'", on macOS "lsof -nP -i :3303", and on Windows "netstat -ano | findstr :3303" to see the local process. From another machine, "nmap -p 3303 <host>" shows whether it is reachable.

05 Related
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