Responder
Responder is a tool for testing name-resolution poisoning (LLMNR, NBT-NS, mDNS) in Windows networks, showing why those protocols should be disabled.
Legal & ethical use. Poisoning name resolution on a production network disrupts users and is illegal without authorisation. Use this tool only on systems, networks and data that you own or have explicit written permission to test. Unauthorised access or scanning can break computer-misuse laws (for example Pakistan's Prevention of Electronic Crimes Act, 2016, and equivalents elsewhere). Practise in your own lab or in authorised environments such as CTFs.
What it is used for
- Demonstrate in a lab why LLMNR/NBT-NS should be disabled
- Test detection of poisoning activity
Key features
- Rogue name-resolution responder
- Captures authentication attempts in a lab
- Analyse mode (passive)
Installation
Install from your distribution or clone the repository (Python).
Beginner usage guide
Use analyse mode first to observe name-resolution traffic without poisoning, and run poisoning only in an isolated lab.
Example commands
Run these only against your own lab or authorised targets. Placeholder addresses such as 192.0.2.x are documentation ranges.
Passive analysis mode
sudo responder -I eth0 -A-I selects the interface and -A analyses traffic without sending poisoned answers.
References
Source verification
Last reviewed: 2026-10-27
Links checked over HTTP: 2026-10-27 07:51 UTC — official: 200, docs: 200, repo: 200
Command flags checked against the real binary responder (__) on 2026-10-27.