Re: An idea: GxSE

[Daniel Senie <dts@senie.com>]

At 02:57 PM 6/21/01, Joe Abley wrote:
>On Thu, Jun 21, 2001 at 02:35:26PM -0400, Daniel Senie wrote:
> > At 02:19 PM 6/21/01, Paul Francis wrote:
> > > >
> > > > 1) Site is multihomed and one of the links to the ISP is broken and
> > > >    how we get around this without breaking any connections.
> > > >
> > > > 2) Site is multihomed and there is a long running e.g. TCP connection
> > > >    which needs to survive in the case of renumbering.
> > > >
> > > > So, we are addressing (1) in this WG. Hence, the use of word 
> renumbering
> > > > is confusing to me. Could somebody clarify this ?
> > > >
> > >
> > >I think, broadly stated, the goal of the wg is to have the same 
> multihoming
> > >functionality with IPv6 as we have with IPv4, but done in a scalable way.
> > >But multi6 is producing a requirements document that will clarify things.
> > >
> > >With IPv4 multihoming today (ignoring the NAT case), case 1 works, so
> > >presumably we want this functionality with IPv6.  Even so, I think in most
> > >cases losing a connection because an ISP went down would be acceptable, as
> > >long as new connections indeed chose the other ISP.
> >
> > 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route with default, withdrawn prefixes are covered by aggregates,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.


> > So, I don't know that there's much problem with the new sessions starting
> > with different addresses, provided end systems are told in some way 
> that an
> > upstream link died (i.e. they have to know to use the other link).
>
>The problem is that the current multi-homing strategies in use with v4
>provide for session stability, and we are trying (as far as is possible)
>to encapsulate the capabilities of the current architecture in the
>requirements for the new one.

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.
-----------------------------------------------------------------
Daniel Senie                                        dts@senie.com
Amaranth Networks Inc.                    http://www.amaranth.com