Re: Minutes / Notes

[Pekka Savola <pekkas@netcore.fi>]

On Mon, 21 Jul 2003, Joe Abley wrote:
> >> Also remember that the effects of a re-homing event
> >> can be felt several levels down; if your path to the DFZ is through
> >> three intermediate ASes, then you're three-times as likely to feel the
> >> impact of a re-homing event if the multihoming architecture presents 
> >> an
> >> impact to be felt. In some countries, *all* the ISPs are two or three
> >> ASes away from the core.
> >
> > Nope, it's not as simple as that.
> >
> > Please remember the context here: we're talking about the connection
> > surviability of the end-user.  What happens several AS's upstream
> > doesn't typically matter *at all*.  Sure, some circuit goes down, and
> > traffic gets re-routed.  These almost always cause a quick re-routing,
> > not e.g.  falling back to BGP hello timeouts. These are not things
> > that are (typically) visible to the end-users, and do not trigger
> > rehoming events.
> 
> Right, that's the case right now.
> 
> However, if a re-homing event between the user and the DFZ forces a 
> renumbering event (for example), and there's no transport-layer support 
> for session stability over that renumbering event, then the user will 
> see their sessions die.

Indeed.

I don't think this is all that common case, though.  I'd really wish to
know of events like these in the DFZ that caused a re-routing delay long
enough (e.g. over 30 secs) to be an annoyance.

> > The most important things, as it seems to me, are:
> >  - your own resiliency
> >  - the connection between you and your ISP(s)
> >  - your first-hop ISP's network characteristics, configuration, etc.
> 
> That is the case with today's IPv4 multi-homing, since the multi-homing 
> model provides endpoint address stability. In the case of an alternate 
> multi-homing model which doesn't provide address stability, users will 
> feel pain.

Yes.  Which is why multiple PA + a tunnel through a second ISP is actually 
a rather good solution (IMHO).  Not enough for everybody, certainly, but 
good nonetheless.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings