[j-nsp] Internet routes in MPLS network, global table or own VRF?

[Keegan Holley]

2012/1/26 Pavel Lunin <plunin at senetsy.ru>:
>
>
>>
>> why would FRR LSP's take a route different than what the IGP would
>> converge to.
>
>
> Because FRR uses a path from a different entry (PLP) to probably a different
> exit (say, next-next-hop). When normal LSP (either SPF or CSPF calculated)
> is a path from head-end to tail-end. Whether this happens often or rare, the
> need to care how your detours are calculated is itself a big enough
> headache.

That's not how FRR works at least for RSVP.  It pretty much just
re-runs cspf with something removed.  So it's the same route your IGP
would choose if said "thing" went dark.  I don't have many obscure
paths where I wouldn't want traffic to go so I can't really comment on
your earlier idea.  That being said I've never seen FRR choose a path
worse than the path the IGP would choose.  It's just preselects that
path and pre-signals it.  I'm sure there are failure scenarios though.


>
>> > What the VRF-based Internet users will definitely notice is (looks like
>> > RAS
>> > is tired of telling this story) is ICMP tunneling and consequent hard to
>> > interpret delay values. People are very suspicious to the numbers. This
>> > is
>> > almost impossible to explain, that the numbers, traceroute shows, have
>> > nothing to do with their kitty-photos-not-loading problem.
>>
>> Hey kitty photos are serious business especially if you are facebook
>> stalking the aforementioned kitty.
>
>
> Absolutely. This is why in case of issues you should not waste time for
> explaining why your core router is 200ms away from the previous hop.
>