csharp-dns-server
Fully functional DNS server written in C#.
The project was conceived while working to reduce the cost of datacentre "stamps" while providing robust services within a datacentre, specifically to remove the need for an expensive load-balancer device by providing round-robin DNS services, and retrying connectivity instead.
Licence
This software is licenced under MIT terms that permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms and the copyright notice. See licence.txt
Getting Started
// clone the repo
>> cd $repo-root
>> git clone https://github.com/stephbu/csharp-dns-server
// check you can build the project
>> cd $repo-root/csharp-dns-server
>> dotnet build
// check that the tests run
>> dotnet test
Gotchas
- if you're running on Windows 10 with Docker Tools installed, Docker uses the ICS SharedAccess service to provide DNS resolution for Docker containers - this listens on UDP:53, and will conflict with the DNS project. Either turn off the the service (
net stop SharedAccess), or change the UDP port.
Features
As written, the server has the following features:
- Pluggable Zone Resolver. Host one or more zones locally, and run your code to resolve names in that zone. Enables many complex scenarios such as:
- round-robin load-balancing. Distribute load and provide failover with a datacentre without expensive hardware.
- health-checks. While maintaining a list of machines in round-robin for a name, the code performs periodic healthchecks against the machines, if necessary removing machines that fail the health checks from rotation.
- Delegates all other DNS lookup to host machines default DNS server(s)
The DNS server has a built-in Web Server providing operational insight into the current server behaviour.
- healthcheck for server status
- counters
- zone information
Interesting Possible Uses
Time-based constraints such as parental controls to block a site, e.g. Facebook. Logging of site usage e.g. company notifications
Challenges
Testing
Two phases of testing was completed.
-
Verification that the bit-packing classes correctly added and removed bits in correct Endian order, complicated by network bitpacking in reverse order to Windows big-endian packing.
-
Protocol verification - that well known messages were correctly decoded and re-encoded using the bit-packing system.
Much time was spent using Netmon to capture real DNS challenges and verify that the C# DNS server responded appropriately.
DNS-Sec
No effort made to handle or respond to DNS-Sec challenges.
Contribution Guide
Pull Requests, Bug Reports, and Feature Requests are most welcome.
Contribution Workflow
Suggested workflow for PRs is
- Make a fork of csharp-dns-server/master in your own repository.
- Create a branch in your own repo to entirely encapsulate all your proposed changes
- Make your changes, add documentation if you need it, markdown text preferred.
- Squash your commits into a single change (Find out how to squash here)
- Submit a PR, and put in comments anything that you think I'll need to help merge and evaluate the changes
Licence Reminder
All contributions must be licenced under the same MIT terms, do include a header file to that effect.