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// Other services

Port 656: SPMP

Port 656 is assigned by IANA to spmp (SPMP).

656

How spmp works

Other services
client:656spmpresponse client:656spmpresponse

The client sends a request to port 656 and the spmp 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 656 dangerous?

We have no specific security note for port 656. 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 656

ServicePortTransportDescriptionReferenceUpdated
spmp 656 TCP, UDP SPMP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 656, and is it reachable?

Linux

sudo ss -ltnup 'sport = :656'      # process listening on 656
sudo lsof -nP -i :656

macOS

sudo lsof -nP -i :656

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 656 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 656
netstat -ano | findstr :656

From another machine

nmap -p 656 -sV <host>
sudo nmap -sU -p 656 <host>
nc -zv <host> 656

Block it in the firewall

sudo ufw deny 656/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 656" -Direction Inbound -LocalPort 656 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 656 used for?

Port 656 is assigned by IANA to spmp (SPMP).

Is port 656 TCP or UDP?

Port 656 is registered for TCP and UDP.

Is it safe to open port 656?

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 656 is open?

On Linux run "ss -ltnup 'sport = :656'", on macOS "lsof -nP -i :656", and on Windows "netstat -ano | findstr :656" to see the local process. From another machine, "nmap -p 656 <host>" shows whether it is reachable.

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