Why are localhost connections blocked by the firewall?

.net sockets tcp firewall socketexception
Muis picture Muis · Jan 20, 2014 · Viewed 24.6k times · Source

When I listen on a port on localhost, Windows will popup a dialogue in which the user must add my program to the list of firewall exceptions. This is annoying, and requires administrator-rights, which the user may not have.

Why does Windows do this for loopback connections (127.0.0.1) and is there some trick to prevent this?

Answer

Muis picture Muis · Jan 20, 2014

The answer was to specify:

IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Loopback, Port);

instead of

IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Any, Port);

for the listening socket. At first sight this seems to prevent any firewall warnings and doesn't require any rules to be added to the firewall. But I have to do some more extensive testing to be sure this works on all Windows configurations.

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