DHCP Server
What is Port 67?
Port 67 is the server-side port for the Dynamic Host Configuration Protocol (DHCP), which automatically assigns IP addresses, subnet masks, gateways, and DNS server information to devices on a network. Defined in RFC 2131, DHCP replaced the older BOOTP protocol and is essential for managing IP addresses in networks of any size. When a device connects to a network, it broadcasts a DHCP Discover message, and DHCP servers listening on port 67 respond with an IP address offer. DHCP uses a four-step process: Discover, Offer, Request, and Acknowledge (DORA). Nearly every home router, enterprise network, and cloud virtual network uses DHCP. Without it, every device would need manually configured network settings.
Common Uses
- Automatic IP address assignment in local networks
- Network configuration distribution (DNS, gateway, NTP)
- IP address lease management and renewal
- PXE boot and network-based OS deployment
Technical Details
Copy-paste commands to check port 67 (DHCP Server) from your terminal
Test connectivity
nmap -p 67 -sU -sV example.com
(echo > /dev/tcp/example.com/67) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 67/udp
sudo iptables -A INPUT -p udp --dport 67 -j ACCEPT
sudo firewall-cmd --permanent --add-port=67/udp && sudo firewall-cmd --reload
Security Considerations
DHCP has no built-in authentication, making it vulnerable to rogue DHCP server attacks where an attacker serves malicious network configurations. DHCP starvation attacks can exhaust the address pool. Use DHCP snooping on managed switches, 802.1X port authentication, and monitor for unauthorized DHCP servers on the network.
Popular Ports Reference
The most commonly used and referenced network ports