What does Dns.GetHostEntry Method(String) actually do?

c# .net dns host system.net
Greg Tarr picture Greg Tarr · Jun 6, 2012 · Viewed 26.8k times · Source

I can't find any proper description in the documentation for what this actually does.

Does it check for the existence of A records or CNAME records or both?

My understanding is that in .NET 4, this throws a SocketException if the host does not exist, and this is confirmed by my testing.

Answer

Martin Liversage picture Martin Liversage · Jun 6, 2012

Dns.GetHostEntry is built on top of the Windows API and does not use the DNS protocol directly. If IPv6 is enabled it will call getaddrinfo. Otherwise it will call gethostbyaddr. These functions may use the local %SystemRoot%\System32\drivers\etc\hosts file, DNS or even NETBIOS to resolve a host name to an IP address. Resolving a host name to an IP address using DNS will use CNAME records to find the A record.

You can test this by resolving www.google.com that at least right now has a CNAME record that points to www.l.google.com. Using Dns.GetHostEntry will return the IP addresses from the A records for www.l.google.com.

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