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

[Mark Tinka]

On Wednesday, October 19, 2011 06:49:31 AM Bradford 
Chatterjee wrote:

> The biggest operational issue that we've encountered is
> that having PE features enabled on your P routers makes
> your core vulnerable to quite a few more bugs. It's not
> necessarily a deal breaker but you do need to be aware
> of it.

Indeed - the edge needs features, which means code upgrades, 
which means problems for your core. We relegate P/PE 
combinations for new, small PoP's where cost is a factor, 
and the customer base is small/simple that the basic 
features we have in the device would be more than sufficient 
to fend off any kinky deployments.

Another area which is one of concern for P/PE designs is 
QoS. We were particularly hit by our Juniper's on this one. 
Traditionally, Juniper remarks packets with your QoS values 
on egress. The problem with this in a P/PE design is that 
you likely have one QoS policy for you core traffic, and 
another for your edge traffic. If you remark on egress, how 
is the router to know which traffic is transit and which is 
edge, as sometimes it's 'popping' and other times it's 
'swapping'?

Of course, newer line cards from Juniper now support ingress 
remarking (closer to the customer), but the majority of 
deployments out there still don't. Suffice it to say, 
ingress remarking on Juniper kit is only advanced on the 
older hardware, i.e., M-series routers with IQ2E-enabled 
PIC's. The MX with it's MX-3D line cards is still far from 
perfect, but better than the previous DPC's.

In 'c-nsp' context, I'm not sure whether any Cisco kit has 
an ingress remarking deficiency, or egress remarking 
affinity (all the Cisco kit we have remarks on ingress just 
fine), but it's something you want to make sure you don't 
get into with the kit you deploy for P/PE functions.

Cheers,

Mark.
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