Port 18243 (clusterxl)

IANA assigns port 18243 to clusterxl: Checkpoint router state backup.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference

clusterxl TCP Checkpoint router state backup Check Point Software -

Registry dates for this port: registered 2012-06-28.

Linux: is anything listening on TCP 18243?

sudo ss -tlnp 'sport = :18243'

Linux / macOS: which process owns the port

sudo lsof -nP -i :18243

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':18243 '

Windows (Command Prompt)

netstat -ano | findstr :18243

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 18243 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 18243

From Windows

Test-NetConnection HOST -Port 18243

ufw

sudo ufw deny 18243/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 18243 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 18243 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 18243' -Direction Inbound -Protocol TCP -LocalPort 18243 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.