On 7/12/07, OBATA Noboru <[EMAIL PROTECTED]> wrote:
> Ian McDonald wrote:
> > On 6/26/07, OBATA Noboru <[EMAIL PROTECTED]> wrote:
> >
> >> From: OBATA Noboru <[EMAIL PROTECTED]>
> >>
> >> Make TCP_RTO_MAX a variable, and allow a user to change it via a
> >> new sysctl entry /proc/sys/net/ipv4/tcp_rto_max. A user can
> >> then guarantee TCP retransmission to be more controllable, say,
> >> at least once per 10 seconds, by setting it to 10. This is
> >> quite helpful on failover-capable network devices, such as an
> >> active-backup bonding device. On such devices, it is desirable
> >> that TCP retransmits a packet shortly after the failover, which
> >> is what I would like to do with this patch. Please see
> >> Background and Problem below for rationale in detail.
> >>
> > RFC2988 says this:
> > (2.4) Whenever RTO is computed, if it is less than 1 second then the
> > RTO SHOULD be rounded up to 1 second.
> >
> > Traditionally, TCP implementations use coarse grain clocks to
> > measure the RTT and trigger the RTO, which imposes a large
> > minimum value on the RTO. Research suggests that a large
> > minimum RTO is needed to keep TCP conservative and avoid
> > spurious retransmissions [AP99]. Therefore, this
> > specification requires a large minimum RTO as a conservative
> > approach, while at the same time acknowledging that at some
> > future point, research may show that a smaller minimum RTO is
> > acceptable or superior.
> >
> > (2.5) A maximum value MAY be placed on RTO provided it is at least 60
> > seconds.
> >
> > Your code doesn't seem to meet requirements of section 2.5 as your
> > minimum is 1 second.
>
> (At the risk of having another Emily Litella moment entering a
> discussion late...)
>
> I thought that those sorts of things were generally referring to the
> _default_ setting?
I believe so. And the requirement of section 2.5 is rather weak
(it says "MAY").
It is weak in saying you don't have to have a maximum, but if you do
have one IT IS AT LEAST 60 seconds (emphasis mine). So the time period
is a strong requirement if you decide to implement - which is a weak
requirement.
Ian
--
Web: http://wand.net.nz/~iam4/
Blog: http://iansblog.jandi.co.nz
WAND Network Research Group
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