Re: An idea: GxSE

[Joe Abley <jabley-ietf@automagic.org>]

On Thu, Jun 21, 2001 at 03:17:37PM -0400, Daniel Senie wrote:
> At 02:57 PM 6/21/01, Joe Abley wrote:
> >On Thu, Jun 21, 2001 at 02:35:26PM -0400, Daniel Senie wrote:
> > > In the present Internet, the sessions already break when a link dies. The
> > > backbone convergence is taking too long for applications in many cases,
> > > from my observations. So, application writers either have to build in
> > > auto-reconnect logic, or their apps are going to have problems.
> >
> >This is not my experience. TCP session stability around a re-homing
> >event (i.e. the session recovers, and does not fail) is common, even
> >when end-points are relatively remote (my experience is between New
> >Zealand and Europe).
> 
> It is my experience with a variety of access services around New England.
> 
> >Remember that full convergence across the internet is not necessary
> >for packets to continue to reach their proscribed destinations; ASes
> >route with default, withdrawn prefixes are covered by aggregates,
> >etc.
> 
> We see the traffic die at the first default-free router. Sessions usually 
> time out while the BGP withdrawals are still flapping around.

I'd be interested to know exactly what you were advertising, and
what failure scenarios cause TCP sessions reliably to die; sounds
like it might be worth comparing it to what we did in 4768, since
our experience is interestingly different. If you would like to
follow this up, please feel free to mail me privately (we can
summarise if there are relevant conclusions).

One question you might ask yourself, however, is whether there might
have been re-homing events elsewhere between your network and the
destination that TCP sessions might have survived without you knowing.
Can you definitely conclude that TCP sessions invariably collapsed?
Or is there a chance that there were other re-homing scenarios during
which TCP sessions survived without you noticing?

> I understand that, but I disagree that the present mechanism works in the 
> real world, so the question is whether it's a worthwhile requirement going 
> forward. You've seen good results in the face of rerouting, I've seen very 
> bad results. Two data points don't tell us a lot. The question should be 
> asked, though, as to whether the present mechanism is working and thus 
> worth keeping, before engraving it in stone for IPv6.


Joe