[c-nsp] OSPF+BGP and MPLS Q's

[adamv0025 at netconsultings.com]

Hi see inline,

> ringbit at mail.com
> Sent: Thursday, July 19, 2018 8:32 PM
> 
> Hi all,
> 
> I have some practical design questions.
> 
> 1. Is there a better way of doing the HA than having adjacencies to the
router
> (can be 3 hops away) over two different VLANs and different OSPF cost over
> trunk links with BFD enabled?
>
I'm not sure I understand the question,
But if you plan on doing:
PE1--PE2--PE3
PE1-vlan100-PE2-vlan200-PE3
PE1----------vlan300--------PE3
This will not increase the resilience of the setup.
As the two paths between PE1 and PE3 will share the same shared resource
groups (SRG) so if one path fails both paths will fail in fact.

> 2. Do you find less practical a MPLS network on a multi-area design vs a
> single-area design?
>
Starting at single area everywhere is always more practical, (you can
monitor ospf statistics SPF calculations in particular from time to time to
see if it's too much for the OSPF to handle). 
Depending on the platform OSPF will scale to 100s of thousands of routes
just fine. 
(beyond 1M -I'm not sure if that request was fulfilled back in the days or
even whether the implementation was made available publically, but other
things like multi-area interfaces did, anyways might be a fun test to do
actually, anyone?).   

> 4. At what point would you introduce RouteReflectors in the network (e.g.
> when 5, 10, 20 IBGP connections?)
> 
Well if you plan on having the whole core provisioning fully automated (e.g.
adding new bgp speaker or routing policy and monitoring) then that doesn't
matter - though the complexity doesn't disappear it's just moved to another
domain. 
With full mesh you'll get all paths visible by all BGP speakers natively
(might or might not be welcome), but there are ways of accomplishing that
even if RRs are used instead of full-mesh (wit e.g. Type-1 RDs in VPNv4/6
AFs and Add-Path in IPv4/6 AFs) -but again, complexity doesn't disappear
it's just moved to another domain.    
Another decision factor worth considering with every new design is where
would you fall in terms of the overall deployments types graph, and I'd say
most of the folks here would *cluster around the RRs deployment, so there's
a lot more knowledge (and bug fixes) around how to handle that type of
complexity in the community in comparison with the camp around full-mesh
iBGP (or fully automated iBGP deployments for that matter). 
 
*pun unintended 
I imagine this multidimensional graph (# of dimensions = config
parameters/features we consider), where regions around MP-BGP with VPNv4 and
OSPF and RRs would be relatively denser and clumped together in comparison
to say regions around MP-BGP with Multicast and EIGRP and full-mesh, I think
of google's zero-shot translation (interlingua graph).  

adam

netconsultings.com
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