DNS Resolver with Domain Filtering

Author

• Patrik Procházka (xprochp00@stud.fit.vut.cz)

Description

This project implements a custom DNS resolver with built-in domain filtering. It listens for incoming DNS queries from clients, checks them against a configurable blocklist, and either resolves allowed queries using upstream DNS server or filter blocked domains.

Features

• Custom domain filtering based on a blocklist
• Supports UDP DNS queries with A records
• Fast domain filtering using a prefix tree
• Dual-stack support for IPv4 and IPv6
• Logs queries and filtered domains

Usage

Program options

./dns -s server [-p port] -f filter_file [-i version] [-r count] [-t time] [-d] [-v] [-h]

Option	Description
-s server	Specify the upstream DNS server to forward allowed queries.
-p port	Optional. Port number the resolver listens on (default: 53).
-f filter_file	Path to the file containing domains to block.
-i version	Optional. Force IP version for upstream queries: 4 for IPv4, 6 for IPv6.
-r count	Optional. Number of retransmits (default: 1).
-t time	Optional. Time to wait for response (default: 500 ms).
-d	Optional. Enable debug mode.
-v	Optional. Enable verbose mode.
-h	Print help message.

Example

./dns -s 8.8.8.8 -p 5353 -f blocked_domains.txt

Project structure

├── README              # Project description
├── Makefile            # Wrapper for gmake on BSD systems
├── real.mk             # Program build configuration
├── src/                # Source code files
├── include/            # Header files
│   └── dns/            
│   └── exceptions/
│   └── logger.hpp
└── tests/              # Project tests
│   └── query/
│   └── resolver/
│   └── trie/
│   └── test.sh
├── docs/               # Project documentation

License / Copyright

© 2025 Patrik Procházka.
All rights reserved. No part of this code may be copied, modified, or redistributed without explicit permission from the author.