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// Other services

Port 6251: TL1 Raw Over SSL/TLS

Port 6251 is assigned by IANA to tl1-raw-ssl (TL1 Raw Over SSL/TLS).

6251

How tl1-raw-ssl works

Other services
client:6251#%&@!x9response? client:6251#%&@!x9response?

The client sends a request to port 6251 and the tl1-raw-ssl service answers. Everything is encrypted: someone on the path only sees unreadable bytes.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
EncryptedTLS or built-in crypto
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Other services
01 Security

Is port 6251 dangerous?

We have no specific security note for port 6251. 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 6251

ServicePortTransportDescriptionReferenceUpdated
tl1-raw-ssl 6251 TCP, UDP TL1 Raw Over SSL/TLS - 2008-01-29

// source: IANA service name and port number registry

03 Check it

Which program uses port 6251, and is it reachable?

Linux

sudo ss -ltnup 'sport = :6251'      # process listening on 6251
sudo lsof -nP -i :6251

macOS

sudo lsof -nP -i :6251

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6251 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 6251
netstat -ano | findstr :6251

From another machine

nmap -p 6251 -sV <host>
sudo nmap -sU -p 6251 <host>
nc -zv <host> 6251

Block it in the firewall

sudo ufw deny 6251/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 6251" -Direction Inbound -LocalPort 6251 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 6251 used for?

Port 6251 is assigned by IANA to tl1-raw-ssl (TL1 Raw Over SSL/TLS).

Is port 6251 TCP or UDP?

Port 6251 is registered for TCP and UDP.

Is it safe to open port 6251?

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 6251 is open?

On Linux run "ss -ltnup 'sport = :6251'", on macOS "lsof -nP -i :6251", and on Windows "netstat -ano | findstr :6251" to see the local process. From another machine, "nmap -p 6251 <host>" shows whether it is reachable.

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