How do I kill the process using port 67?

On macOS & Linux, run: "sudo systemctl stop isc-dhcp-server || sudo killall dhcpd". On Windows PowerShell (as Admin), run: "Stop-Service DHCPServer -Force".

Why am I getting "port 67 already in use" (EADDRINUSE)?

This occurs when another background instance of dhcpd, dnsmasq, isc-dhcp-server or a zombie process is already bound to port 67. Use the kill commands above to free the port immediately.

Networking

Risk: Medium

Port 67 — DHCP Server (Bootstrap Protocol)

Q: Is Port 67 safe to expose to the public internet?

Risk level is Medium. Rogue DHCP servers on an untrusted local network can assign malicious DNS resolvers and default gateways, leading to Man-in-the-Middle (MitM) attacks. Implement DHCP snooping on network switches.

Port 67 is used by DHCP (Dynamic Host Configuration Protocol) servers to receive broadcast lease requests from client devices seeking IP configuration on local subnets.

PORT NUMBER

PROTOCOL

UDP

DEFAULT PROCESS

dhcpd, dnsmasq, isc-dhcp-server

FIREWALL TARGET

67/udp

Instant Terminal Fixes for Port 67

macOS & Linux Terminal

1. Check who is listening on port 67:

sudo ss -ulpn | grep ":67 "

2. Kill process occupying port 67 (EADDRINUSE fix):

sudo systemctl stop isc-dhcp-server || sudo killall dhcpd

3. UFW Firewall Allow rule:

sudo ufw allow 67/udp

Windows PowerShell (Admin)

1. Check listening port:

Get-NetUDPEndpoint -LocalPort 67

2. Force kill process on port 67:

Stop-Service DHCPServer -Force

3. Docker Port Forwarding Mapping:

docker run -d --net=host -v /etc/dhcp:/data networkboot/dhcpd eth0

Common Error Encountered

dhcpd: Address already in use or interface not configured for DHCP broadcasts.

Security Advisory & Hardening

Rogue DHCP servers on an untrusted local network can assign malicious DNS resolvers and default gateways, leading to Man-in-the-Middle (MitM) attacks. Implement DHCP snooping on network switches.

Frequently Asked Questions

Port 67 Questions & Answers

Common questions regarding default services, kill commands, and firewall configurations.

Port 67 is commonly used for DHCP Server (Bootstrap Protocol). Port 67 is used by DHCP (Dynamic Host Configuration Protocol) servers to receive broadcast lease requests from client devices seeking IP configuration on local subnets.

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