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Port 4138 (nettest)

IANA assigns port 4138 to nettest.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
nettest TCP nettest David Borman -
nettest UDP nettest David Borman -

Registry dates for this port: registered 2003-03.

Check what is listening on port 4138

Linux: is anything listening on TCP 4138?
sudo ss -tlnp 'sport = :4138'
Linux: UDP 4138
sudo ss -ulnp 'sport = :4138'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4138
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4138 '
Windows (Command Prompt)
netstat -ano | findstr :4138
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4138 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4138
From Windows
Test-NetConnection HOST -Port 4138
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4138

Block port 4138 in the firewall

ufw
sudo ufw deny 4138/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4138 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4138 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4138' -Direction Inbound -Protocol TCP -LocalPort 4138 -Action Block
ufw
sudo ufw deny 4138/udp
iptables
sudo iptables -A INPUT -p udp --dport 4138 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4138 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4138' -Direction Inbound -Protocol UDP -LocalPort 4138 -Action Block

Related ports

4136cl-db-request4137cl-db-remote4139thrtx4140cedros-fds, cedros_fds

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