Re: [PATCH 1/1] tcp: Wrong timeout for SYN segments

On Wed, 2012-08-22 at 12:00 +0200, Eric Dumazet wrote:

On Wed, 2012-08-22 at 11:29 +0200, Alex Bergmann wrote:

quoted

Actual 6 SYN frames are sent. The initial one and 5 retries.

first one had a t0 + 0 delay. How can it count ???

quoted

The kernel is waiting another 32 seconds for a SYN+ACK and then gives 
the ETIMEDOUT back to userspace.

Do you mean that we have to send another SYN packet after the 3 minutes?

First SYN is not a retransmit

R2 = time_of_last_SYN - time_of_initial_SYN (t0) = 31

If you read RFC it states :

"In particular, R2 for a SYN segment MUST
 be set large enough to provide retransmission of the segment
 for at least 3 minutes."


That means that the last _retransmit_ MUST happen after 180 seconds.

And not :

Send all the restransmits at t0 + 1, then wait 180 seconds before giving
connect() a timeout indication.

Therefore, the minimal connect() timeout should be : 180 + 100 seconds

(allowing 100 seconds for the SYNACKs sent in answer of the very last
retransmit to come back)

(100 seconds is the R2 for non SYN frames)

RFC quote : The value of R2 SHOULD
            correspond to at least 100 seconds.