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Port 6251 (tl1-raw-ssl)

IANA assigns port 6251 to tl1-raw-ssl: TL1 Raw Over SSL/TLS.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
tl1-raw-ssl TCP TL1 Raw Over SSL/TLS Jim Humphreys -
tl1-raw-ssl UDP TL1 Raw Over SSL/TLS Jim Humphreys -

Registry dates for this port: registered 2008-01-29.

Check what is listening on port 6251

Linux: is anything listening on TCP 6251?
sudo ss -tlnp 'sport = :6251'
Linux: UDP 6251
sudo ss -ulnp 'sport = :6251'
Linux / macOS: which process owns the port
sudo lsof -nP -i :6251
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':6251 '
Windows (Command Prompt)
netstat -ano | findstr :6251
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 6251 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 6251
From Windows
Test-NetConnection HOST -Port 6251
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 6251

Block port 6251 in the firewall

ufw
sudo ufw deny 6251/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 6251 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 6251 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 6251' -Direction Inbound -Protocol TCP -LocalPort 6251 -Action Block
ufw
sudo ufw deny 6251/udp
iptables
sudo iptables -A INPUT -p udp --dport 6251 -j DROP
nftables
sudo nft add rule inet filter input udp dport 6251 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 6251' -Direction Inbound -Protocol UDP -LocalPort 6251 -Action Block

Related ports

6243jeol-nsdtp-3, jeol-nsddp-36244jeol-nsdtp-4, jeol-nsddp-46252tl1-ssh6253crip

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.