dhcpstuff

DHCP Discover sender and response analyzer for network diagnostics: broadcasts a DHCPDISCOVER and prints every answer, including regular DHCP offers and Proxy DHCP responses from PXE boot servers. Standard library only.

Modules

• dhcp_discover.py — builds a DHCPDISCOVER packet, broadcasts it to 255.255.255.255:67 from UDP port 68 and collects replies for the given timeout. Only replies matching the transaction ID are shown. Each response is labelled DHCP <type> or, if the offered address (yiaddr) is 0.0.0.0, Proxy DHCP <type>, followed by offered IP, next server, server name, boot file and all parsed options with human-readable names. With --arch the Discover carries PXE client architecture (option 93) and a matching PXEClient vendor class (option 60), which Proxy DHCP / PXE boot servers require before they answer.
• __main__.py — makes python3 -m somestuff.dhcpstuff run the same CLI.

Installation

pip install somestuff-dhcpstuff

somestuff is a PEP 420 namespace; the package is imported as somestuff.dhcpstuff and shares the namespace with the other somestuff-* distributions.

Usage

Console script and module invocation are equivalent:

sudo dhcp-discover
sudo python3 -m somestuff.dhcpstuff.dhcp_discover
sudo python3 -m somestuff.dhcpstuff

Examples:

# Basic discover on all interfaces
sudo dhcp-discover

# Specific interface, PXE EFI64 architecture
sudo dhcp-discover -i eth0 -a efi64

# Custom MAC and longer timeout
sudo dhcp-discover -m 02:aa:bb:cc:dd:ee -t 10

Library

from somestuff.dhcpstuff import build_discover, mac_bytes, parse_response

packet = build_discover(mac_bytes("02:aa:bb:cc:dd:ee"), xid=0x12345678)

The package also exports parse_options, print_response, format_option, fmt_ip, fmt_mac, main and the constants DHCP_SERVER_PORT, DHCP_CLIENT_PORT, MAGIC_COOKIE, DHCP_MSG_TYPES, DHCP_OPTIONS and PXE_ARCH_TYPES.

Privileges

dhcp-discover binds UDP port 68 and needs root (or CAP_NET_BIND_SERVICE). It will not work while another DHCP client holds the port exclusively.

Notes

• The repository additionally contains diagnose-dhcp.sh, a root-only (German) shell script for finding unwanted DHCP on physical interfaces of Ubuntu Server (cloud-init, Netplan, systemd-networkd, NetworkManager, DHCP client processes, lease files, ip=dhcp kernel cmdline, udev/dispatcher hooks). It is not part of the installed package: https://github.com/vroomfondel/somestuff/tree/main/somestuff/dhcpstuff/
• Requires: no third-party dependencies. Linux only (SO_BINDTODEVICE).
• Licensed under the LGPL, see LICENSE.md in the repository root.