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// Other services

Port 3731: Service Manager

Port 3731 is assigned by IANA to smap (Service Manager).

3731

How smap works

Other services
client:3731smapresponse client:3731smapresponse

The client sends a request to port 3731 and the smap 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 3731 dangerous?

We have no specific security note for port 3731. 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 3731

ServicePortTransportDescriptionReferenceUpdated
smap 3731 TCP, UDP Service Manager - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 3731, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3731'      # process listening on 3731
sudo lsof -nP -i :3731

macOS

sudo lsof -nP -i :3731

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3731 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3731
netstat -ano | findstr :3731

From another machine

nmap -p 3731 -sV <host>
sudo nmap -sU -p 3731 <host>
nc -zv <host> 3731

Block it in the firewall

sudo ufw deny 3731/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3731" -Direction Inbound -LocalPort 3731 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3731 used for?

Port 3731 is assigned by IANA to smap (Service Manager).

Is port 3731 TCP or UDP?

Port 3731 is registered for TCP and UDP.

Is it safe to open port 3731?

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 3731 is open?

On Linux run "ss -ltnup 'sport = :3731'", on macOS "lsof -nP -i :3731", and on Windows "netstat -ano | findstr :3731" to see the local process. From another machine, "nmap -p 3731 <host>" shows whether it is reachable.

05 Related
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