[Valmar]

For me, the turn off was that any ipv6 connection on Linux was ALWAYS slow as hell to resolve, often leading to timeouts. Tore my hair out for ages, only to discover after much frustration and searching online that the solution was as simple as disabling the kernel's ipv6 module.

With ipv4, never had a problem.

[acdha]

That’s a local configuration error but it’s common enough that the community standardized a better approach which is widely implemented now:

https://tools.ietf.org/html/rfc6555