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// Other services

Port 6551: Software Update Manager

Port 6551 is assigned by IANA to sum (Software Update Manager).

6551

How sum works

Other services
client:6551sumresponse client:6551sumresponse

The client sends a request to port 6551 and the sum 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 6551 dangerous?

We have no specific security note for port 6551. 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 6551

ServicePortTransportDescriptionReferenceUpdated
sum 6551 TCP, UDP Software Update Manager - 2007-12-13

// source: IANA service name and port number registry

03 Check it

Which program uses port 6551, and is it reachable?

Linux

sudo ss -ltnup 'sport = :6551'      # process listening on 6551
sudo lsof -nP -i :6551

macOS

sudo lsof -nP -i :6551

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6551 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 6551
netstat -ano | findstr :6551

From another machine

nmap -p 6551 -sV <host>
sudo nmap -sU -p 6551 <host>
nc -zv <host> 6551

Block it in the firewall

sudo ufw deny 6551/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 6551" -Direction Inbound -LocalPort 6551 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 6551 used for?

Port 6551 is assigned by IANA to sum (Software Update Manager).

Is port 6551 TCP or UDP?

Port 6551 is registered for TCP and UDP.

Is it safe to open port 6551?

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 6551 is open?

On Linux run "ss -ltnup 'sport = :6551'", on macOS "lsof -nP -i :6551", and on Windows "netstat -ano | findstr :6551" to see the local process. From another machine, "nmap -p 6551 <host>" shows whether it is reachable.

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