dn_comp - Linux


dn_comp is a command-line tool designed to perform domain name compression as specified in RFC 1035. It takes a DNS packet in text format as input and compresses it by replacing repeated domain names with pointers to their first occurrence. Compression reduces the size of the packet, making it more efficient to transmit.


dn_comp [options] <input_file> <output_file>


  • -h, –help: Display help and usage information.
  • -v, –verbose: Enable verbose output, providing additional details about the compression process.
  • -f, –force: Overwrite the output file if it already exists.
  • -q, –quiet: Suppress all output except for errors.


Simple Compression:

dn_comp example.txt compressed.txt

Verbose Compression with Output to STDOUT:

dn_comp -v example.txt | tee compressed.txt

Force Overwrite of Existing File:

dn_comp -f compressed.txt backup.txt

Common Issues

  • Invalid Input File: Ensure that the input file contains a valid DNS packet in text format.
  • Output File Permission Denied: Check if the user has sufficient write permissions to create or overwrite the output file.
  • Memory Exhaustion: If the input DNS packet is exceptionally large, it may exceed the available memory, causing dn_comp to fail. Consider splitting the packet into smaller chunks.


Combine with tcpdump:

Capture network traffic and filter for DNS packets using tcpdump, then pipe the output to dn_comp for compression:

tcpdump -i eth0 -w capture.pcap
dn_comp capture.pcap compressed.txt

Use as a Preprocessor:

Preprocess DNS packets before further analysis or manipulation:

dn_comp input.txt | analyze_dns

Related Commands

  • tcpdump: Network traffic capture and analysis
  • nslookup: DNS lookup and query tool
  • dig: Advanced DNS lookup and debugging tool