[j-nsp] Avoid transit LSPs

[adamv0025 at netconsultings.com]

> From: Luis Balbinot <luis at luisbalbinot.com>
> Sent: Monday, January 28, 2019 1:39 PM
> 
> I have many LSPs from P1 to P4 and all have FRR protection (Juniper FRR, 1:1).
> Even with two distinct paths from P1 to P4 (both with much lower IGP
> metrics) I get some detour LSPs setup on PE1. PE1 is a low-end ACX5k with
> very limited transit capabilities and I definitely don't want any transit traffic
> through it.
> 
> I could color the green links and call them "p-pe" for example but I can't just
> exclude all "p-pe" links from the FRR selection. If I setup an LSP from P1 to
> PE1 the CSPF path will be P1->P2->PE1 and I'll need the P1->P2->P3->PE1
> path for protection, but that can't be setup because it has a "p-pe" member
> in the path.
> 
> P2->PE1 and P3->PE1 share the same fate as P2->P3, but even with SRLG
> it is not guaranteed that LSPs won't be setup over the PE1 circuits.
> 
I think what could be done in this topology is to mark the P2-PE1 and P3-PE1 links with special colour (say green for the sake of this example).
1) Now as for the RSVP-TE signalled LSPs between P routers (e.g. between P1 and P4)
Those would be set up to exclude green colour when signalling their detour LSPs.
[edit protocols mpls label-switched-path LSP_P1_TO_P4]
set fast-reroute exclude GREEN
2) only LSPs to PE1 will have no such constrain configured for their detour LSPS.
And thus will be able to use the P2-PE1 and P3-PE1 links in order to protect the last leg of the path towards PE1

adam