Port 3921 (herodotus-net)

IANA assigns port 3921 to herodotus-net: Herodotus Net.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

herodotus-net TCP Herodotus Net Adam Gawne Cain -

herodotus-net UDP Herodotus Net Adam Gawne Cain -

Registry dates for this port: registered 2003-11.

Linux: is anything listening on TCP 3921?

sudo ss -tlnp 'sport = :3921'

Linux: UDP 3921

sudo ss -ulnp 'sport = :3921'

Linux / macOS: which process owns the port

sudo lsof -nP -i :3921

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':3921 '

Windows (Command Prompt)

netstat -ano | findstr :3921

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3921 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 3921

From Windows

Test-NetConnection HOST -Port 3921

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 3921

ufw

sudo ufw deny 3921/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 3921 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 3921 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 3921' -Direction Inbound -Protocol TCP -LocalPort 3921 -Action Block

ufw

sudo ufw deny 3921/udp

iptables

sudo iptables -A INPUT -p udp --dport 3921 -j DROP

nftables

sudo nft add rule inet filter input udp dport 3921 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 3921' -Direction Inbound -Protocol UDP -LocalPort 3921 -Action Block

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