[dns-operations] To A or to AAAA - was Re: Signaling client

[Tony Finch]

On Mon, 17 Jan 2011, Edward Lewis wrote:
>
> I would restate Doug's "right answer" to be - fix applications (which includes
> OS') to ask for all possible means to reach a resource and then try all
> possible means until a working one is found.

The important thing is to try all of them at the same time. The usual IPv6
failure mode is an unpleasant timeout. If it works but you get routed
through a shitty 6to4 gateway, it isn't then obvious that tearing down the
connection and retrying with IPv4 would be better. Hence, try them all at
once and the first connection to be able to transfer data wins.

The standard protocol-agnstic getaddrinfo API isn't great because you
can't be sure that it is implemented well, i.e. that it makes all the name
service queries symultaneously. It also doesn't allow you to overlap name
service queries with connection initiation. So perhaps we want a new API
to attempt concurrent connections on all the results from getaddrinfo,
plus a higher-level call that bundles the two together and which could
reduce latency further.

Tony.
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