Port 4020 (trap)

IANA assigns port 4020 to trap: TRAP Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

trap TCP TRAP Port Jeffrey C Byrd -

trap UDP TRAP Port Jeffrey C Byrd -

Linux: is anything listening on TCP 4020?

sudo ss -tlnp 'sport = :4020'

Linux: UDP 4020

sudo ss -ulnp 'sport = :4020'

Linux / macOS: which process owns the port

sudo lsof -nP -i :4020

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':4020 '

Windows (Command Prompt)

netstat -ano | findstr :4020

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4020 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 4020

From Windows

Test-NetConnection HOST -Port 4020

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

nc -vzu -w 5 HOST 4020

ufw

sudo ufw deny 4020/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 4020 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 4020 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 4020' -Direction Inbound -Protocol TCP -LocalPort 4020 -Action Block

ufw

sudo ufw deny 4020/udp

iptables

sudo iptables -A INPUT -p udp --dport 4020 -j DROP

nftables

sudo nft add rule inet filter input udp dport 4020 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 4020' -Direction Inbound -Protocol UDP -LocalPort 4020 -Action Block

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