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Port 4373 (remctl)

IANA assigns port 4373 to remctl: Remote Authenticated Command Service.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
remctl TCP Remote Authenticated Command Service Russ Allbery -
remctl UDP Remote Authenticated Command Service Russ Allbery -

Registry dates for this port: registered 2007-08-30.

Check what is listening on port 4373

Linux: is anything listening on TCP 4373?
sudo ss -tlnp 'sport = :4373'
Linux: UDP 4373
sudo ss -ulnp 'sport = :4373'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4373
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4373 '
Windows (Command Prompt)
netstat -ano | findstr :4373
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4373 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4373
From Windows
Test-NetConnection HOST -Port 4373
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4373

Block port 4373 in the firewall

ufw
sudo ufw deny 4373/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4373 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4373 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4373' -Direction Inbound -Protocol TCP -LocalPort 4373 -Action Block
ufw
sudo ufw deny 4373/udp
iptables
sudo iptables -A INPUT -p udp --dport 4373 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4373 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4373' -Direction Inbound -Protocol UDP -LocalPort 4373 -Action Block

Related ports

4371l2c-control, l2c-disc4372l2c-data4374psi-ptt4375tolteces

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