Port 68 (DHCP client (BOOTP))

DHCP clients receive offers and acknowledgements on UDP 68.

Well-known (system) port, 0-1023 UDP Network infrastructure Localhost or LAN only

Port 68 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

What port 68 is used for

DHCP clients receive offers and acknowledgements on UDP 68.

Localhost or LAN only. Must be allowed inbound on the client's local interface for DHCP to work; never needed from the internet.

Service nameProtoDescriptionAssigneeReference

bootpc TCP Bootstrap Protocol Client Bill Croft -

bootpc UDP Bootstrap Protocol Client Bill Croft -

Linux: UDP 68

sudo ss -ulnp 'sport = :68'

Linux / macOS: which process owns the port

sudo lsof -nP -i :68

Windows (Command Prompt)

netstat -ano | findstr :68

Windows (PowerShell)

Get-NetUDPEndpoint -LocalPort 68

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

nc -vzu -w 5 HOST 68

ufw

sudo ufw deny 68/udp

iptables

sudo iptables -A INPUT -p udp --dport 68 -j DROP

nftables

sudo nft add rule inet filter input udp dport 68 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 68' -Direction Inbound -Protocol UDP -LocalPort 68 -Action Block

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