Port 621 (escp-ip)

IANA assigns port 621 to escp-ip: ESCP.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

escp-ip TCP ESCP Lai Zit Seng -

escp-ip UDP ESCP Lai Zit Seng -

Linux: is anything listening on TCP 621?

sudo ss -tlnp 'sport = :621'

Linux: UDP 621

sudo ss -ulnp 'sport = :621'

Linux / macOS: which process owns the port

sudo lsof -nP -i :621

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':621 '

Windows (Command Prompt)

netstat -ano | findstr :621

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 621 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 621

From Windows

Test-NetConnection HOST -Port 621

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

nc -vzu -w 5 HOST 621

ufw

sudo ufw deny 621/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 621 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 621 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 621' -Direction Inbound -Protocol TCP -LocalPort 621 -Action Block

ufw

sudo ufw deny 621/udp

iptables

sudo iptables -A INPUT -p udp --dport 621 -j DROP

nftables

sudo nft add rule inet filter input udp dport 621 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 621' -Direction Inbound -Protocol UDP -LocalPort 621 -Action Block

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