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Port 6551 (sum)

IANA assigns port 6551 to sum: Software Update Manager.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
sum TCP Software Update Manager Jan Dirven -
sum UDP Software Update Manager Jan Dirven -

Registry dates for this port: registered 2007-12-13.

Check what is listening on port 6551

Linux: is anything listening on TCP 6551?
sudo ss -tlnp 'sport = :6551'
Linux: UDP 6551
sudo ss -ulnp 'sport = :6551'
Linux / macOS: which process owns the port
sudo lsof -nP -i :6551
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':6551 '
Windows (Command Prompt)
netstat -ano | findstr :6551
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 6551 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 6551
From Windows
Test-NetConnection HOST -Port 6551
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 6551

Block port 6551 in the firewall

ufw
sudo ufw deny 6551/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 6551 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 6551 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 6551' -Direction Inbound -Protocol TCP -LocalPort 6551 -Action Block
ufw
sudo ufw deny 6551/udp
iptables
sudo iptables -A INPUT -p udp --dport 6551 -j DROP
nftables
sudo nft add rule inet filter input udp dport 6551 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 6551' -Direction Inbound -Protocol UDP -LocalPort 6551 -Action Block

Related ports

6549apc-65496550fg-sysupdate6556checkmk-agent6566sane-port

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