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Port 3718 (opus-services)

IANA assigns port 3718 to opus-services: OPUS Server Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
opus-services TCP OPUS Server Port Detlef Stoever -
opus-services UDP OPUS Server Port Detlef Stoever -

Registry dates for this port: registered 2003-03.

Check what is listening on port 3718

Linux: is anything listening on TCP 3718?
sudo ss -tlnp 'sport = :3718'
Linux: UDP 3718
sudo ss -ulnp 'sport = :3718'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3718
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3718 '
Windows (Command Prompt)
netstat -ano | findstr :3718
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3718 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3718
From Windows
Test-NetConnection HOST -Port 3718
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3718

Block port 3718 in the firewall

ufw
sudo ufw deny 3718/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3718 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3718 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3718' -Direction Inbound -Protocol TCP -LocalPort 3718 -Action Block
ufw
sudo ufw deny 3718/udp
iptables
sudo iptables -A INPUT -p udp --dport 3718 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3718 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3718' -Direction Inbound -Protocol UDP -LocalPort 3718 -Action Block

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