IPAddress.TryParse expects and out parameters. That parameter doesn't have to be initialized. For your code it can be:
System.Net.IPAddress throwawayIpAddress; //No need to initialize it
if(System.Net.IPAddress.TryParse(baseUri.Host, out throwawayIpAddress))
{
//valid IP address
}
{
//Invalid IP address
}
If the parsing is successful then your object throwawayIpAddress
will have the valid IP address, you can use it further in the code or ignore it if you want.