Expose a global switch to disable IPV6 to overcome DualMode socket issues in environments that do not support IPV6

[antonfirsov]

BCL as well as external libraries tend to shift towards dual-stack sockets in their networking code. This conforms to best practices defined in RFC1933, but can lead to issues when connections are established through VPN tunnels which do not support IPv6 and/or dual-stack properly.

A custom ConnectCallback can help in HttpClient use cases where users have direct control over their HttpClient instances (#47267), but in cases where the Socket connections are carried out by an external component, users may get blocked (#45462).

This cases are rare, but the fix is simple, and easy to communicate (see #45893), therefore we should consider implementing it in .NET 6.

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Issue Details

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BCL and external libraries tend to shift towards dual-stack sockets in their networking code. This conforms to best practices defined in RFC1933, but can lead to issues when connections are established through VPN tunnels which do not support IPv6 and/or dual-stack properly.

A custom ConnectCallback can help in HttpClient use cases where users have direct control over their HttpClient instances (#47267), but in cases where the Socket connections are carried out by an external component, users may get blocked (#45462).

This cases are rare, but the fix is simple, and easy to communicate (see #45893), therefore we should consider implementing it in .NET 6.

Author:	antonfirsov
Assignees:	-
Labels:	area-System.Net, untriaged
Milestone:	-

[karelz]

Would it make sense to generalize it to global switch to disable either IPv4 or IPv6?

[geoffkizer]

Would it make sense to generalize it to global switch to disable either IPv4 or IPv6?

I doubt it. I haven't heard any issues re IPv4.

Even if we wanted to do this, I think it would be a separate switch.

[karelz]

Triage: We cannot do today IPv6 only, so let's add DisableIPv6 switch.

[karelz]

Another case in #52287