Resolution

Resolution is a simple utility for resolving DNS records.

Packages

Current version: 2.0.0

Target Frameworks: .NET standard 2

Dependencies

• None.

Development Dependencies

• Microsoft.NET.Test.SDK
• NUnit
• NUnit3TestAdapter

Usage

The Resolver class serves as the core of this library. It takes the given domain and question type and performs the required DNS lookups. By default, it will use the system default DNS servers but can be configured to use alternatives.

The simplest way to use Resolver is to use the static Query(string domainName, QuestionType questionType, string dnsServer = null, QuestionClass questionClass = QuestionClass.In) method.

    var response = Resolver.Query("status.github.com", QuestionType.Cname, "1.1.1.1");

The above example queries the Cloudflare DNS server at "1.1.1.1" for the CNAME record of status.github.com. If the dnsServer parameter is null the system DNS will be used.

The Resolver class can also be configured for re-use using ResolverFactory.GetResolver(IEnumerable<string> dnsServers = null, int cacheSize = 1000, int retries = 3, TransportType transportType = TransportType.Udp, int timeout = 1, bool useCache = false, bool useRecursion = true).

The Resolver configuration options are:

• IEnumerable<string> dnsServers, a collection of DNS server IP addresses.

• int cacheSize, size of the response cache.

• int retries, the number of times a query is retried.

• TransportType transportType, the query transport type, either UDP or TCP.

• int timeout, the query timeout in seconds.

• bool useCache, indicates if resolver should create and use an in-memory response cache.

• bool useRecursion, indicates if the resolver should use query recursion.

    # Get a caching resolver using Cloudflare DNS at 1.1.1.1
    var resolver = ResolverFactory.GetResolver(dnsServers: new string[]{"1.1.1.1"}, useCache: true);
  

Defaults

The following are the defaults for the static Resolver.Query() method or ResolverFactory.GetResolver() with no parameters.

• DNS servers: The system DNS servers.
• Retries: 3.
• Timeout: 1 second.
• Recursion: True.
• Caching: None.
• Cache Size: 1,000

Caching

The resolver caching is rudimentary and not thread-safe. By default 1,000 responses are stored in the cache. The eviction strategy uses the oldest last access time of a cache item. In other words, if the cache size limit is reached items will be evicted in order of last access to make room for new items.

References

• IANA DNS page