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// Other services

Port 3556: Sky Transport Protocol

Port 3556 is assigned by IANA to sky-transport (Sky Transport Protocol).

3556

How sky-transport works

Other services
client:3556sky-transportresponse client:3556sky-transportresponse

The client sends a request to port 3556 and the sky-transport 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 3556 dangerous?

We have no specific security note for port 3556. 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 3556

ServicePortTransportDescriptionReferenceUpdated
sky-transport 3556 TCP, UDP Sky Transport Protocol - 2002-07

// source: IANA service name and port number registry

03 Check it

Which program uses port 3556, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3556'      # process listening on 3556
sudo lsof -nP -i :3556

macOS

sudo lsof -nP -i :3556

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3556 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3556
netstat -ano | findstr :3556

From another machine

nmap -p 3556 -sV <host>
sudo nmap -sU -p 3556 <host>
nc -zv <host> 3556

Block it in the firewall

sudo ufw deny 3556/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3556" -Direction Inbound -LocalPort 3556 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3556 used for?

Port 3556 is assigned by IANA to sky-transport (Sky Transport Protocol).

Is port 3556 TCP or UDP?

Port 3556 is registered for TCP and UDP.

Is it safe to open port 3556?

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 3556 is open?

On Linux run "ss -ltnup 'sport = :3556'", on macOS "lsof -nP -i :3556", and on Windows "netstat -ano | findstr :3556" to see the local process. From another machine, "nmap -p 3556 <host>" shows whether it is reachable.

05 Related
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