Kestrel throws when specifying `*` IP binding on OS without IPv6 support

[aelij]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

.NET 10 added a new check when setting Socket.DualMode = true that throws a PlatformNotSupportedException if the underlying OS doesn't support IPv6.

This causes Kestrel to throw when specifying listen URLs such as https://*:443. This is a regression from .NET 9.

Expected Behavior

No exception

Steps To Reproduce

No response

Exceptions (if any)

fail: Microsoft.Extensions.Hosting.Internal.Host[11]
      Hosting failed to start
      System.PlatformNotSupportedException: Operation is not supported on this platform.
         at System.Net.Sockets.Socket.set_DualMode(Boolean value)
         at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketTransportOptions.CreateDefaultBoundListenSocket(EndPoint endpoint)
         at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketConnectionListener.Bind()
         at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketTransportFactory.BindAsync(EndPoint endpoint, CancellationToken cancellationToken)
         at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.TransportManager.BindAsync(EndPoint endPoint, ConnectionDelegate connectionDelegate, EndpointConfig endpointConfig, CancellationToken cancellationToken)

.NET Version

10.0.0

Anything else?

No response

[BrennanConroy]

@pavelsavara

[pavelsavara]

@aelij which OS are we talking about ?

[pavelsavara]

The change is from #106977

And the setter looks like this now:

runtime/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs

Lines 760 to 767 in ba80e54

	if (AddressFamily != AddressFamily.InterNetworkV6)
	{
	throw new NotSupportedException(SR.net_invalidversion);
	}
	if (!OSSupportsIPv6DualMode && value) throw new PlatformNotSupportedException();
	SetSocketOption(SocketOptionLevel.IPv6, SocketOptionName.IPv6Only, value ? 0 : 1);

We were already asserting that AddressFamily is InterNetworkV6 before that PR. The setter is setting a IPv6Only option.

How this was legit use-case in Net9 ?

[aelij]

@pavelsavara Azure Linux 3.0, but I think it's because it's hosted on an AKS cluster that only has IPv4 enabled.

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[pavelsavara]

https://github.com/dotnet/aspnetcore/blob/c9d0750396e1d319301255ba61842721ab72ab10/src/Servers/Kestrel/Transport.Sockets/src/SocketTransportOptions.cs#L143-L148

[pavelsavara]

I'm able to reproduce this with Environment.SetEnvironmentVariable("DOTNET_SYSTEM_NET_DISABLEIPV6", "1"); on windows