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Re: DNS round-robin timeout

From: Tim Bannister <>
Date: Tue, 17 Jan 2012 16:09:10 +0000

On Tue, Jan 17, 2012, Daniel Stenberg wrote:
> On Fri, 13 Jan 2012, Pierre Ynard wrote:
> >libcurl tries each IP address sequentially and divides the timeout
> >value between all of them. Let's say that I set a connection
> >timeout of 2 seconds, which seems plenty reasonable for normally
> >responsive hosts. Let's say that I hit a host pointing to 10 IP
> >addresses. 2s / 10 = 200 ms, so despite my reasonable 2 seconds
> >timeout, libcurl will try to connect to every IP with a timeout of
> >only 200 ms.
> Yeah. It has been one of those things nagging in the back of my head
> for years and we really should improve it. The question is, of
> course, what the best approach really is.

Might this be better done as example code for

I like the pattern where there are up to N simultaneous connection
attempts: initially one attempt to a random address from the pool,
then after a timeout a second simultaneous attempt is started.

Once a connection is established, cancel the other connections.

With suitable parameters this is not unfair on the server side and
allows the maximum possible time for a slow server to respond.

However, it's too complicated to put into libcurl itself.

Tim Bannister -
List admin:
Received on 2012-01-17