Re: Redirection to Other IP Addresses

Bin Ni <> Thu, 01 August 2019 10:15 UTC

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From: Bin Ni <>
Date: Thu, 1 Aug 2019 03:12:16 -0700
Message-ID: <>
To: Daniel Stenberg <>
Cc: Jack Firth <>, Chris Lemmons <>, Amos Jeffries <>, HTTP Working Group <>
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Subject: Re: Redirection to Other IP Addresses
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Hi Daniel,

At high level, my proposal is in every other way the same as today's 30X
With this in mind, the answer to your questions are:
1. In general, the alternate IP should only be used once for the next
single request.
But there is nothing to prevent the clients from remembering it, which is
Just like there is nothing to prevent a client to disregard the DNS TTL.
They do it with their own risk.
2. This proposal is to fix some limitations of the 30X with Location header.
Not very helpful to make it work together with the Location header.
3. We are not requiring every server and every client to support this
For the ones who find it to be useful, the "extra burden" is a non-issue.



On Thu, Aug 1, 2019 at 2:18 AM Daniel Stenberg <> wrote:

> On Thu, 1 Aug 2019, Bin Ni wrote:
> > 2. my proposed behavior:
> > Client: Hi Server-, can you send me the movie XXX?
> > Server- Sorry, I can't give you the movie, you need to ask server
> > for this movie.
> > Client: Hi Server-, can you send me the movie XXX?
> > Server- Here is the movie.
> > (It then took 0.5 hours to deliver the movie, because server- is
> > closer to the client, or less loaded)
> If we for a moment play with the idea that we'd do something like this,
> then I
> think it should be aligned with and work together with Alt-Svc in a better
> way
> than what is currently proposed...
> There's no max-age/TTL. For how long is the user-agent supposed to
> consider
> the alternative IP addresses as the only ones that the given origin has?
> Forever? Only for the next single connect (attempt)?
> Are the alternative IPs supposed to be used for the entire origin or for
> that
> specific URI only?
> A 3xx redirect without a Location: header? Wouldn't it make more sense and
> work more similar to existing 3xx redirects if it also sends a Location:?
> Then
> existing clients that don't understand 312 might have a higher chance of
> at
> least doing something sensible.
> If a client gets this response and starts downloading huge content from
> the
> new IP and the client then opens a second connection to the origin in a
> second
> tab. Which IPs is that supposed to use? The original ones or the
> redirected
> ones?
> Requring user-agent snooping for a server to figure out if the feature
> works
> or not is a totally broken idea and I think this detail needs to be worked
> out
> for this idea to be considered for real.
> My personal preference is probably to add some sort of "urgency" thing to
> alt-svc instead of this 312 plus several headers, so that a client can be
> told
> that it should switch sooner rather than later.
> --
>   /


Bin Ni
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