67 DHCP-server UDP
Reference for UDP port 67, commonly associated with DHCP-server.
What it's for
Port 67 is the port a DHCP (Dynamic Host Configuration Protocol) server listens on to hand out IP addresses and network configuration (gateway, DNS servers, lease time) to devices joining a network. Whenever a device connects to a Wi-Fi network or a wired switch and automatically gets an IP address without manual configuration, DHCP running on this port is what made that happen.
Protocol basics
DHCP uses UDP because the whole handshake happens before a device even has an IP address — there's no established connection to build a TCP session on top of. The classic exchange (DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, DHCPACK) is broadcast-based: a joining client broadcasts a discovery message, and the server responds from port 67 to port 68 on the client. Because it relies on broadcasts, DHCP is inherently a local-network protocol — reaching across subnets requires a DHCP relay agent forwarding requests to a central server.