Cannot listen to port on ALL interfaces "0.0.0.0"

I found that you cannot do a ForwardedPortLocal/Remote if the bound host is set to "0.0.0.0" or IPAddress.Any.ToString().
The .NET will throw an exception.

I think your problem is in the ForwardedPortLocal:InternalStart() method. I think when you create the IPEndPoint you should do:

IPEndPoint ipEndPoint;
if (this.BoundHost == IPAddress.Any.ToString()) // Or however you want to compare
ipEndPoint = new IPEndPoint(IPAddress.Any, (int) this.BoundPort);
else
ipEndPoint = new IPEndPoint(DnsAbstraction.GetHostAddresses(this.BoundHost)[0], (int) this.BoundPort);

Similarly, the constructor, ForwardedPortRemote(string boundHost, uint boundPort, string host, uint port)
creates the IPAddress of the bound host exaclty the same way, by calling Dns.GetHostAdresses().

I am not sure if you did this on purpose to try to NOT support IPAddress.Any, however, it is clear there are cases when this is needed, and in fact other libraries (SecureBlackBox) support it.

I see you allow boundHost to be string.Empty, but shouldn't then you be doing the conversion to IPAdress.Any directly?

Start with ForwardedPortLocal:InternalStart() and the ForwardedPortRemote(string boundHost, uint boundPort, string host, uint port) constructor, then inspect how DnsAbstraction resolves the bound host before creating an IPEndPoint. The change is done when forwarding accepts "0.0.0.0" and an empty bound host without the reported .NET exception.