[c-nsp] Downsides of combining P and PE functions into a single box

[Keegan Holley]

2011/10/19 Mark Tinka <mtinka at globaltransit.net>

> On Thursday, October 20, 2011 12:49:39 AM Keegan Holley
> wrote:
>
> > +1 on the $$$.   Still PE is one network P+PE is
> > essentially two networks.
>
> No. P + P/PE is one network.
>
> P + P/PE are two devices.
>

Maybe I was a bit loose with the details here.  My only point was that the
portion of the network where the P routers live has different rules than the
edge.

>
> > I still don't see how this
> > adds to complexity.  For most commonly used features the
> > per-hop-behavior is the same on the PE router whether
> > the packet came from a core P router or another PE
> > router.
>
> There are many features that are not turned on on core
> routers, which are on edge routers.
>
> I can't recall the last time I logged into our core routers
> for anything other than to add a new link. You don't want to
> know how often our Provisioning team are logging into the PE
> routers.
>
> If one PE router goes down, I don't have to worry about 25%
> of the country feeling the pinch, as I have that
> abstraction.
>

Well I think we both can agree that the network you work in requires P
routers for a number of reasons.  I understand the feature differences
between the P and PE routers.  The point was that people implement P routers
for different reasons, but not for their own sake.  I wouldn't use a
collapsed core to route 25% of a county let alone a country.

>
> > Maybe I'm missing something, but PE routers are
> > not going everywhere and if we're strictly talking about
> > complexity it's easier to manage one network instead of
> > 2.
>
> It's all one network. What's more than one is the devices,
> not the network itself.
>
> Even if it may seem trivial, it's important to make this
> distinction, because successful networks are always scaling
> up, and scaling up means buying more kit whether we like it
> or not, i.e., device numbers go up, sometimes because you
> want to delineate functions.
>

+1
I like the pay as you grow model.  If you are small just use a collapsed
core.  As your customer base grows you can move customers to create a core
layer or just buy more links and more boxes.  Chances are that if the
original poster needed a separate core he wouldn't be here asking the
question.