Re: Alt-Svc over DNS

On Tue, Jan 16, 2018 at 1:59 PM, Lucas Pardue <>

> Hi Ben,
> This is an interesting proposal. I like that this could provide a pathway
> to launching QUIC connections without depending on legacy HTTP.


Some thoughts:
> This seems a bit like delegated Alt-Svc. Responsibilities for
> advertisement are no longer solely the Origins responsibility.
> Is "clear" accommodated? There might be some subtle differences in how a
> client maintains their cache here. E.g we have a client that touches the
> cache on every response with Alt-Svc, an alternative can quickly remove
> itself by issuing clear before the ma expiration.

Interesting.  I think as a server operator, if you want to be able to do
this kind of cache purging, you can't use ALTSVC.  DNS is fundamentally not
compatible with cache purging.  We could add some text to that effect.

Presumably in cases where the host is omitted from Alt- Svc record, a
> client must also wait for A or AAAA. How would it know which IP to use
> here? This seems to introduce a change, currently a particular IP
> advertises it's alternatives. Is there a danger of resolving to the wrong
> thing?Do we need a AAAALTSVC record ;)

I don't think this generates any meaningful change: ALTSVC is scoped to the
origin, not to an IP.  If a client is performing A and AAAA queries, then
it's a dual-stack client starting happy eyeballs.  The client just does
happy eyeballs with these IP addresses, and the connection parameters
specified in ALTSVC.

If you think it's unclear we can add text for it, but it seems pretty
straightforward to me.  We could equivalently say that it's as if you got
an Alt-Svc that included the origin as the hostname, and then had to do
happy eyeballs to connect.

Kind regards
> Lucas
> ________________________________________
> From: Ben Schwartz []
> Sent: 16 January 2018 17:25
> To:
> Subject: Alt-Svc over DNS
> As Mike Bishop noted last month, "Alt-Svc in DNS keeps coming up" [1].
> Now Mike and I have a draft describing how that would work:
> Putting Alt-Svc information in the DNS offers both performance and privacy
> advantages.  Please take a look!
> --Ben
> P.S. I admit this design bears a suspicious resemblance to Erik Nygren's
> "B" record proposal from 2014 [2].
> [1]
> [2]

Received on Tuesday, 16 January 2018 20:55:58 UTC