Custom DNS Resolver

This project implements a DNS resolver that performs iterative queries from root servers down to authoritative name servers to resolve domain names to IP addresses.

Features

• Reads root server hints from root.hints
• Contacts root, TLD, and authoritative DNS servers via UDP
• Constructs and parses DNS query and response packets manually
• Supports DNS query types A (IPv4 address) and NS (Name Server)
• Caches DNS records locally with TTL support
• Handles additional and authority DNS sections including glue records
• Uses threading for concurrent query handling and periodic cache purging
• Implements EDNS(0) OPT pseudo-record for extended DNS features

How It Works

See detailed explanation and design in Note.md.

1. Initialization
   Loads root server IPs from root.hints file.

2. Finding Nearest Root Server
   Measures latency to root servers and selects the fastest for queries.

3. DNS Query Construction
   Builds DNS query packets including headers, questions, and optional EDNS record.

   +---------------------+
   | Header              |
   +---------------------+
   | Question            |
   +---------------------+
   | Answer              | 
   +---------------------+
   | Authority           | 
   +---------------------+
   | Additional          | 
   +---------------------+
   

4. Iterative Resolution

   • Query root server for TLD servers for the domain.
   • Query TLD servers for it returns namerserver domain + glued ip (only if in same zone) like .com tld only will give hostinger.com nameserver ip not hostinger.net ip.
   • Query authoritative servers for the final IP address.

   root server --> tld server --> nameserver

   note:- sometimes tld only return nameserver domain name (because of out-zone) .so we have to start new query from starting for finding namerserver iproot server --> tld server -->(gluedip)

5. Response Parsing
   Parses DNS response sections: answers, authority, and additional records.

   rootserver server returns:- only authority tld server server returns :- authority + additional nameserver returns :- answer

6. Caching
   Stores resolved DNS records with TTL and purges expired entries periodically. we used lmdb incache memory for fast reponse

7. UDP Server
   Listens locally on UDP port 1234 for incoming DNS queries and responds using cache or fresh resolution.

Usage

• Run the resolver: it listens on 127.0.0.1:1234 UDP for DNS queries.
• Queries are resolved by iterative DNS lookup and answered with cached or fresh data.
• Logs resolution steps and latency for debugging.

Requirements

• Python 3.x
• cache.py module for DNS record caching and management

Limitations

• Supports only basic DNS query types (A and NS).
• No DNSSEC or advanced security features.
• Assumes IPv4-only queries and responses.
• Timeout handling with retries is basic.

Future Improvements

• Support for other query types (AAAA, MX, TXT).
• Full DNSSEC validation.
• Better error handling and retry logic.
• IPv6 support.
• Performance optimizations and asynchronous IO.

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This project demonstrates low-level DNS protocol handling and iterative resolver mechanics suitable for learning network programming and DNS internals.