Re: draft-ietf-v6ops-routing-guidelines-00.txt

[Mark Smith <ipng@69706e6720323030352d30312d31340a.nosense.org>]

Hi Kevin,

On Fri, 08 Sep 2006 21:05:28 -0400
Kevin Loch <kloch@kl.net> wrote:

> Mark Smith wrote:
> > 2.6.  Default Route
> > ~~~~~~~~~~~~~~~~~~~
> > "The default unicast route (::) may be advertised in an IGP.  In an
> >    EGP, it may be only advertised to the downstream but must not be
> >    advertised in the core."
> > 
> > I think the SP LB-IGP/EGP model would be a possible to exeception to
> > this, in the sense that "core" would probably be considered by most
> > people to be the core of the local network, rather than the Internet
> > "core". Maybe that could be clarified.
> 
> Any network accepting :: would be by definition a "downstream" and such
> mistakes tend to be rapidly self-correcting (at least in v4).
> 
> Here is an alternative paragraph:
> 
> "The default unicast route (::) may be advertised in an IGP or EGP.  It
> MUST NOT be advertised in an EGP unless it has been requested by the
> recipient.
> 

While it's probably starting to get into pedantry, here's the scenario
I'm thinking of. I work for a smaller SP, where we have two upstream
transit providers, one primary, one backup. We're receiving full route
tables from both of them. However, internally, and we're moving mainly
to an IGP-LB/EGP everything else model, we distribute the full routes
from the primary transit into our internal transit routers, and then
generate a default towards the backup, so we have a default in our EGP,
that's very rarely if ever used, excepting if our primary transit
provider loses visibility to any parts of the Internet. Distributing
the backup link's routes into our network, even just to our primary
border router, gives the longest match rule a chance to override
LOCAL_PREF to our primary. A default injected into our EGP makes our
backup link an absolute last resort.

So, as per your suggested paragraph above, for our network, we're both
the originator and the recipient of the default, or we're downstream of
ourselves :-)

Regards,
Mark.