Re: Check for internet connection

There's no way to tell if a computer is not connected to the Internet 100%
reliably.  There are certain things you can do to mitigate timeouts and
exceptions; but you must make sure you handle those exceptions in case
the connection goes down after your check and before you attempt your
first connection.

The simplest, is to just catch the exception; as you've seen.  There's two
parts to a connection, the name resolution and the connection.  The name
resolution is where the exception is being thrown.  There's also a bug in
the framework with respect to asynchronous IO via an HTTP connection; the
name lookup part isn't performed asynchronously...

You can use the Dns.GetHostEntry() to manually perform the name lookup;
but if it can't connect to the NIC's DNS server an exception will be
thrown.  Without PInvoking WinSock's gethostbyname you'll have to catch
that exception.

You can mitigate that by using NetworkInterface.GetIsNetworkAvailable().
Again, this only mitigates connection issues.  GetIsNetworkAvailable gets
the operational status of the non-tunnel and non-loopback interfaces at
that instance in time; it could very well have just been dropped (it will
return true if just one of the interfaces is considered operational).
Plus, it doesn't do anything to test if your DNS server is up or not--
which will result in the same exception if the DNS server is not
responding (i.e. there's no way to tell from an connection exception if
your Internet isn't working or the DNS isn't responding).  Further, you
could use the IPInterfaceProperties.DnsAddress property on each applicable
result of NetworkInterface.GetIPProperties() and use
NetworkInformation.Ping to ping the DNS before a name resolution or a
connection attempt...

Apologies if parts of this is a repeat of previous posts, I simply read
your last post about not having to handle the exception and tried to put
two and two together (but may have resulted in three)...