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Port 6456 (skip-cert-send)

IANA assigns port 6456 to skip-cert-send: SKIP Certificate Send.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
skip-cert-send TCP SKIP Certificate Send Tom Markson -
skip-cert-send UDP SKIP Certificate Send Tom Markson -

Check what is listening on port 6456

Linux: is anything listening on TCP 6456?
sudo ss -tlnp 'sport = :6456'
Linux: UDP 6456
sudo ss -ulnp 'sport = :6456'
Linux / macOS: which process owns the port
sudo lsof -nP -i :6456
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':6456 '
Windows (Command Prompt)
netstat -ano | findstr :6456
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 6456 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 6456
From Windows
Test-NetConnection HOST -Port 6456
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 6456

Block port 6456 in the firewall

ufw
sudo ufw deny 6456/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 6456 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 6456 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 6456' -Direction Inbound -Protocol TCP -LocalPort 6456 -Action Block
ufw
sudo ufw deny 6456/udp
iptables
sudo iptables -A INPUT -p udp --dport 6456 -j DROP
nftables
sudo nft add rule inet filter input udp dport 6456 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 6456' -Direction Inbound -Protocol UDP -LocalPort 6456 -Action Block

Related ports

6446mysql-proxy6455skip-cert-recv6464ieee11073-207016471lvision-lm

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