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Improve libcli/dns

Samba comes with its own asynchronous DNS parser framework developed for the internal DNS server. Basic calls have been implemented for a client-side library as well, but a more fleshed out implementation would be needed. The goal of this project is to implement more high-level calls handling DNS requests, such as UDP/TCP switchover and client-side GSS-TSIG cryptography. A test suite excercising all the functions is required and can be used to cross-check and complement the existing DNS server tests already shipped by Samba. This testsuite should use cmocka.

  • Difficulty: Medium
  • Language(s): C
  • Mentors: Kai Blin, David Disseldorp
  • Student: Dimitris Gravanis

Client-side DNS call handling with GSS-TSIG

Unix SMB/CIFS implementation

Dimitrios Gravanis (C) 2017

Based on the existing work by Samba Team


For the Samba AD DC, libcli/dns is a library that allows the handling of DNS calls (send/receive requests) and generates GSS-TSIG type encryption signature for signed packets, to accomodate encrypted client-server communication.

It consists of its respective function and structure libraries, that provide definitions for client-side functionality.

Test suites are also available, that inspect individual features of cli_dns.c

For more information on the project goals, read the GSoC proposal [here](

The project timeline and development journal is documented in its dedicated [blogspot](

DNS Client (with wrapper support)

Handles TCP and UDP requests.

The client may use either TCP or UDP protocols to send a DNS name request to the server, then handle the reception of the appropriate server response.


  • UDP request send/receive
  • TCP request send/receive
  • GSS-TSIG generation
  • DNS name packet parsing and signing

The library consists of cli_dns.c, that includes functions, and dns.h, libtcp.h, libtsig.h, libudp.h, that provide declarations, definitions and structures.

      1. Wrapping

wrap_cli.c provides multiple wrapping of the above functionality, to hide buffer creation, DNS packet parsing and signature generation. Definitions of the wrapped functions are provided in libwrap.h.