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// Network services

Port 9131: Dynamic Device Discovery

Port 9131 is assigned by IANA to dddp (Dynamic Device Discovery).

9131

How dddp works

Network services
client:9131dddpresponse client:9131dddpresponse

The client sends a request to port 9131 and the dddp 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 9131 dangerous?

We have no specific security note for port 9131. 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 9131

ServicePortTransportDescriptionReferenceUpdated
dddp 9131 TCP, UDP Dynamic Device Discovery - 2005-08

// source: IANA service name and port number registry

03 Check it

Which program uses port 9131, and is it reachable?

Linux

sudo ss -ltnup 'sport = :9131'      # process listening on 9131
sudo lsof -nP -i :9131

macOS

sudo lsof -nP -i :9131

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9131 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 9131
netstat -ano | findstr :9131

From another machine

nmap -p 9131 -sV <host>
sudo nmap -sU -p 9131 <host>
nc -zv <host> 9131

Block it in the firewall

sudo ufw deny 9131/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 9131" -Direction Inbound -LocalPort 9131 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 9131 used for?

Port 9131 is assigned by IANA to dddp (Dynamic Device Discovery).

Is port 9131 TCP or UDP?

Port 9131 is registered for TCP and UDP.

Is it safe to open port 9131?

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 9131 is open?

On Linux run "ss -ltnup 'sport = :9131'", on macOS "lsof -nP -i :9131", and on Windows "netstat -ano | findstr :9131" to see the local process. From another machine, "nmap -p 9131 <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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