[j-nsp] Transit composite next hops

[adamv0025 at netconsultings.com]

> Luis Balbinot
> Sent: Saturday, February 10, 2018 6:17 PM
> 
> Hi.
> 
> I was reading about composite chained next hops and it was not clear to me
> whether or not MX routers support them for transit traffic. According to
the
> doc bellow it's only a QFX10k/PTX thing:
> 
> https://www.juniper.net/documentation/en_US/junos/topics/reference/co
> nfiguration-statement/transit-edit-routing-options-chained.html
> 
> But there are some contradictions like this document:
> 
> https://www.juniper.net/documentation/en_US/junos/topics/concept/mpl
> s-vpns-chained-composite-next-hops.html
> 
> Which is correct? Juniper docs on this subject, specially transit CNHs,
are very
> superficial. The MX Series book does not mention it and the MPLS in the
SDN
> Era only explains how the ingress CNHs work.
> 
The MX Series books are useless if you want to understand how MX routers
actually work.
I suggest you read through Dave Roy's work instead (for free):
https://www.juniper.net/uk/en/training/jnbooks/day-one/networking-technologi
es-series/packet-walkthrough-mx-series/
http://junosandme.over-blog.com/article-junos-load-balancing-part-1-introduc
tion-105738134.html -related to indirect next hops (and "CCNHs")

My understanding is that "ingress" and "transit" in relation to CCNHs is
just a very misleading nomenclature. 
If you want to go by definition CCNHs are pointers between VPN and NH label
-and transit boxes have no knowledge of VPN labels so go figure... 

But there are still several levels of indirection in the next hop chain that
transit routers can leverage in their FIBs. 

So what is the use case you're interested in? 
Is it whether if your P-core box sees 10K PEs behind AE0 interface and has a
ECMP or FRR-backup path via AE1, whether all these 10K will be swung in one
go without this "transit CCNH" feature enabled? 
-as for this specific one I'm not sure since the show outputs I did suggest
that each of these would have their own NH index.  

adam


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