Re: dual stack & IPv6 on by default

[Mika Liljeberg <mika.liljeberg@welho.com>]

On Sun, 2003-03-09 at 00:00, Alain Durand wrote:
> RFC1122, section 4.2.3.5 says more just bellow what you quote:
> 
>              However, the values of R1 and R2 may be different for SYN
>              and data segments.  In particular, R2 for a SYN segment MUST
>              be set large enough to provide retransmission of the segment
>              for at least 3 minutes.  The application can close the
>              connection (i.e., give up on the open attempt) sooner, of
>              course.
> 
>              DISCUSSION:
>                   Some Internet paths have significant setup times, and
>                   the number of such paths is likely to increase in the
>                   future.
> 
> ==> I understand from that section that a TCP implementation should
>          wait 3 minutes on a SYN-sent before timing out.

This bit applies to the case when there is no feedback (no RST or ICMP
error received by the sender).

>         Do I miss something? Is this recommendation widely ignored?

I don't think it's ignored but, as I said, some implementations take a
bit more liberal view to which ICMP errors can abort the connect phase.

There is some variation to the initial retransmit timeouts and retry
counts in different implementations, though. Linux defaults to 5 SYN
retransmissions, which comes pretty close to 3 minutes with the standard
3 second initial RTO. I recall some versions of Solaris starting with a
1 second RTO and timing out roughly after one minute.

	MikaL