HTTPfy

Port 6556 (checkmk-agent)

IANA assigns port 6556 to checkmk-agent: Checkmk Monitoring Agent.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference
checkmk-agent TCP Checkmk Monitoring Agent Checkmk GmbH -

Registry dates for this port: registered 2020-07-14, last modified 2024-08-06.

Check what is listening on port 6556

Linux: is anything listening on TCP 6556?
sudo ss -tlnp 'sport = :6556'
Linux / macOS: which process owns the port
sudo lsof -nP -i :6556
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':6556 '
Windows (Command Prompt)
netstat -ano | findstr :6556
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 6556 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 6556
From Windows
Test-NetConnection HOST -Port 6556

Block port 6556 in the firewall

ufw
sudo ufw deny 6556/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 6556 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 6556 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 6556' -Direction Inbound -Protocol TCP -LocalPort 6556 -Action Block

Related ports

6550fg-sysupdate6551sum6566sane-port6568canit-store, canit_store, rp-reputation

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