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// Other services

Port 403: decap

Port 403 is assigned by IANA to decap (decap).

403

How decap works

Other services
client:403decapresponse client:403decapresponse

The client sends a request to port 403 and the decap 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 403 dangerous?

We have no specific security note for port 403. 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 403

ServicePortTransportDescriptionReferenceUpdated
decap 403 TCP, UDP decap - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 403, and is it reachable?

Linux

sudo ss -ltnup 'sport = :403'      # process listening on 403
sudo lsof -nP -i :403

macOS

sudo lsof -nP -i :403

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 403 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 403
netstat -ano | findstr :403

From another machine

nmap -p 403 -sV <host>
sudo nmap -sU -p 403 <host>
nc -zv <host> 403

Block it in the firewall

sudo ufw deny 403/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 403" -Direction Inbound -LocalPort 403 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 403 used for?

Port 403 is assigned by IANA to decap (decap).

Is port 403 TCP or UDP?

Port 403 is registered for TCP and UDP.

Is it safe to open port 403?

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 403 is open?

On Linux run "ss -ltnup 'sport = :403'", on macOS "lsof -nP -i :403", and on Windows "netstat -ano | findstr :403" to see the local process. From another machine, "nmap -p 403 <host>" shows whether it is reachable.

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