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// Network services

Port 3951: PWG IPP Facsimile

Port 3951 is assigned by IANA to pwgippfax (PWG IPP Facsimile).

3951

How pwgippfax works

Network services
client:3951pwgippfaxresponse client:3951pwgippfaxresponse

The client sends a request to port 3951 and the pwgippfax 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
Network services
01 Security

Is port 3951 dangerous?

We have no specific security note for port 3951. Its risk depends on the program actually listening on it. General advice for network services services:

  • Answer only the networks that need the service (no open resolvers, relays or reflectors).
  • UDP services can be abused for DDoS amplification: rate-limit or block them at the edge.
  • Disable legacy test services that have no use in production.
02 Registry

IANA registry entries for port 3951

ServicePortTransportDescriptionReferenceUpdated
pwgippfax 3951 TCP, UDP PWG IPP Facsimile - 2004-08

// source: IANA service name and port number registry

03 Check it

Which program uses port 3951, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3951'      # process listening on 3951
sudo lsof -nP -i :3951

macOS

sudo lsof -nP -i :3951

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3951 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3951
netstat -ano | findstr :3951

From another machine

nmap -p 3951 -sV <host>
sudo nmap -sU -p 3951 <host>
nc -zv <host> 3951

Block it in the firewall

sudo ufw deny 3951/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3951" -Direction Inbound -LocalPort 3951 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3951 used for?

Port 3951 is assigned by IANA to pwgippfax (PWG IPP Facsimile).

Is port 3951 TCP or UDP?

Port 3951 is registered for TCP and UDP.

Is it safe to open port 3951?

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. Answer only the networks that need the service (no open resolvers, relays or reflectors).

How do I check if port 3951 is open?

On Linux run "ss -ltnup 'sport = :3951'", on macOS "lsof -nP -i :3951", and on Windows "netstat -ano | findstr :3951" to see the local process. From another machine, "nmap -p 3951 <host>" shows whether it is reachable.

05 Related
:53 DNS tcp · udp · moderate risk :135 MS RPC tcp · udp · high risk :123 NTP udp · tcp · moderate risk :67 DHCP server udp · tcp · moderate risk :111 rpcbind tcp · udp · high risk :9100 Raw printing (JetDirect) tcp · udp · high risk :631 IPP / CUPS tcp · udp · high risk :5353 mDNS udp · tcp · moderate risk

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