- 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.
Port 55: ISI Graphics Language
Port 55 is assigned by IANA to isi-gl (ISI Graphics Language).
55
How isi-gl works
Other servicesThe client sends a request to port 55 and the isi-gl 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
Is port 55 dangerous?
We have no specific security note for port 55. Its risk depends on the program actually listening on it. General advice for other services services:
IANA registry entries for port 55
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| isi-gl | 55 | TCP, UDP | ISI Graphics Language | - | - |
// source: IANA service name and port number registry
Which program uses port 55, and is it reachable?
Linux
sudo ss -ltnup 'sport = :55' # process listening on 55
sudo lsof -nP -i :55macOS
sudo lsof -nP -i :55
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 55 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 55 netstat -ano | findstr :55
From another machine
nmap -p 55 -sV <host> sudo nmap -sU -p 55 <host> nc -zv <host> 55
Block it in the firewall
sudo ufw deny 55/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 55" -Direction Inbound -LocalPort 55 -Protocol TCP -Action Block # Windows
What is port 55 used for?
Port 55 is assigned by IANA to isi-gl (ISI Graphics Language).
Is port 55 TCP or UDP?
Port 55 is registered for TCP and UDP.
Is it safe to open port 55?
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 55 is open?
On Linux run "ss -ltnup 'sport = :55'", on macOS "lsof -nP -i :55", and on Windows "netstat -ano | findstr :55" to see the local process. From another machine, "nmap -p 55 <host>" shows whether it is reachable.
Other other services ports
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