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Port 3781 (abcvoice-port)

IANA assigns port 3781 to abcvoice-port: ABCvoice server port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
abcvoice-port TCP ABCvoice server port Carlos Gonzalez Roma -
abcvoice-port UDP ABCvoice server port Carlos Gonzalez Roma -

Registry dates for this port: registered 2003-06.

Check what is listening on port 3781

Linux: is anything listening on TCP 3781?
sudo ss -tlnp 'sport = :3781'
Linux: UDP 3781
sudo ss -ulnp 'sport = :3781'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3781
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3781 '
Windows (Command Prompt)
netstat -ano | findstr :3781
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3781 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3781
From Windows
Test-NetConnection HOST -Port 3781
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3781

Block port 3781 in the firewall

ufw
sudo ufw deny 3781/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3781 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3781 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3781' -Direction Inbound -Protocol TCP -LocalPort 3781 -Action Block
ufw
sudo ufw deny 3781/udp
iptables
sudo iptables -A INPUT -p udp --dport 3781 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3781 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3781' -Direction Inbound -Protocol UDP -LocalPort 3781 -Action Block

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