- 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.
Port 6556: Checkmk Monitoring Agent
Port 6556 is assigned by IANA to checkmk-agent (Checkmk Monitoring Agent).
6556
How checkmk-agent works
Other servicesThe client sends a request to port 6556 and the checkmk-agent service answers.
- Transport
- TCP
- Exposure risk
- not rated depends on the program listening
- Encryption
- Unknownnot stated by the registry
- IANA status
- Assigned1 registered service
- Range
- Registered (1024-49151)
- Category
- Other services
Is port 6556 dangerous?
We have no specific security note for port 6556. Its risk depends on the program actually listening on it. General advice for other services services:
IANA registry entries for port 6556
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| checkmk-agent | 6556 | TCP | Checkmk Monitoring Agent | - | 2024-08-06 |
| - | 6556 | - | Reserved | - | - |
// source: IANA service name and port number registry
Which program uses port 6556, and is it reachable?
Linux
sudo ss -ltnup 'sport = :6556' # process listening on 6556
sudo lsof -nP -i :6556macOS
sudo lsof -nP -i :6556
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 6556 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 6556 netstat -ano | findstr :6556
From another machine
nmap -p 6556 -sV <host> nc -zv <host> 6556
Block it in the firewall
sudo ufw deny 6556/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 6556" -Direction Inbound -LocalPort 6556 -Protocol TCP -Action Block # Windows
What is port 6556 used for?
Port 6556 is assigned by IANA to checkmk-agent (Checkmk Monitoring Agent).
Is port 6556 TCP or UDP?
Port 6556 is registered for TCP.
Is it safe to open port 6556?
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 6556 is open?
On Linux run "ss -ltnup 'sport = :6556'", on macOS "lsof -nP -i :6556", and on Windows "netstat -ano | findstr :6556" to see the local process. From another machine, "nmap -p 6556 <host>" shows whether it is reachable.
Other other services ports
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp