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// Other services

Port 6511: Datagram Congestion Control Protocol Encapsulation for NAT Traversal

Port 6511 is assigned by IANA to dccp-udp (Datagram Congestion Control Protocol Encapsulation for NAT Traversal).

6511

How dccp-udp works

Other services
client:6511dccp-udpresponse client:6511dccp-udpresponse

The client sends a request to port 6511 and the dccp-udp service answers.

Transport
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 6511 dangerous?

We have no specific security note for port 6511. 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 6511

ServicePortTransportDescriptionReferenceUpdated
dccp-udp 6511 UDP Datagram Congestion Control Protocol Encapsulation for NAT Traversal RFC 6773 -
-6511-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 6511, and is it reachable?

Linux

sudo ss -ltnup 'sport = :6511'      # process listening on 6511
sudo lsof -nP -i :6511

macOS

sudo lsof -nP -i :6511

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6511 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 6511
netstat -ano | findstr :6511

From another machine

nmap -p 6511 -sV <host>
sudo nmap -sU -p 6511 <host>
nc -zv <host> 6511

Block it in the firewall

sudo ufw deny 6511/udp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 6511" -Direction Inbound -LocalPort 6511 -Protocol UDP -Action Block  # Windows
04 FAQ
What is port 6511 used for?

Port 6511 is assigned by IANA to dccp-udp (Datagram Congestion Control Protocol Encapsulation for NAT Traversal).

Is port 6511 TCP or UDP?

Port 6511 is registered for UDP.

Is it safe to open port 6511?

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 6511 is open?

On Linux run "ss -ltnup 'sport = :6511'", on macOS "lsof -nP -i :6511", and on Windows "netstat -ano | findstr :6511" to see the local process. From another machine, "nmap -p 6511 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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