few big monolithic PEs vs many small PEs

Wed Jun 19 20:22:45 UTC 2019

Hi folks,

Recently I ran into a peculiar situation where we had to cap couple of PE
even though merely a half of the rather big chassis was populated with
cards, reason being that the central RE/RP was not able to cope with the
combined number of routes/vrfs/bgp sessions/etc.. 

So this made me think about the best strategy in building out SP-Edge
nowadays (yes I'm aware of the centralize/decentralize pendulum swinging
every couple of years).
The conclusion I came to was that *currently the best approach would be to
use several medium to small(fixed) PEs to replace a big monolithic chasses
based system.
So what I was thinking is, 
Yes it will cost a bit more (router is more expensive than a LC)
Will end up with more prefixes in IGP, more BGP sessions etc.. -don't care.
But the benefits are less eggs in one basket, simplified and hence faster
testing in case of specialized PEs and obviously better RP CPU/MEM to port
ratio.
Am I missing anything please?  

*currently,
Yes some old chassis systems or even multi-chassis systems used to support
additional RPs and offloading some of the processes (e.g. BGP onto those)
-problem is these are custom hacks and still a single OS which needs
rebooting LC/ASICs when being upgraded -so the problem of too many eggs in
one basket still exists (yes cisco NCS6k and recent ASR9k lightspeed LCs are
an exception) 
And yes there is the "node-slicing" approach from Juniper where one can
offload CP onto multiple x86 servers and assign LCs to each server (virtual
node) - which would solve my chassis full problem -but honestly how many of
you are running such setup? Exactly. And that's why I'd be hesitant to
deploy this solution in production just yet. I don't know of any other
vendor solution like this one, but who knows maybe in 5 years this is going
to be the new standard. Anyways I need a solution/strategy for the next 3-5
years.

Would like to hear what are your thoughts on this conundrum.

adam 

netconsultings.com
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