[c-nsp] LDPv6 Census Check

[Robert Raszuk]

/* removing nanog list as I am not subscribed there and it bounces back */

> I found multi-level IS-IS to be useless in an MPLS network because you
still need to leak routes between L2 and L1 in order to form
> MPLS FEC's. So you simplify the network by having a single L2 (or just
Area 0 in OSPF), because today's control planes can handle it.

Spot on ! OSPF is not any better.

And yes you can build a global flat IGP. But this is not a design I would
endorse in most networks.

Reason is that most networks do not have latest connectivity restoration
techniques and still wait for typical "IGP convergence" So if you flood
globally you need to adjust your IGP & SPF timers with the notion of global
flooding.

If you however scope your flooding domains to be relatively small (say per
1-few regions in a continent) you can easily and safely make those timers
much more aggressive hence significantly reducing connectivity restoration
times upon failures.

Many thx,
R.




On Thu, Jun 11, 2020 at 12:15 PM Mark Tinka <mark.tinka at seacom.mu> wrote:

>
>
> On 11/Jun/20 11:57, Robert Raszuk wrote:
>
>
> Nope that was not the main reason.
>
> Main reason was the belief that labels MUST be locally significant - and
> not domain wide unique. Just look at Juniper's SRm6 or now SRH ... they
> keep this notion of locally significant SIDs. It is deep in their DNA ...
> still.
>
> We argued about it a lot in cisco back in TDP days - and we lost.
>
>
> I get this for VLAN's, being only 4,096 per broadcast domain and all.
>
> But are we struggling with scaling label space?
>
> Just my 1+1, since I may be over-simplifying the issue.
>
>
>
> - - -
>
> Now to your runt that MPLS is great because of exact match perhaps you
> missed it but number of solutions on the table (including RbR[**] I
> recently proposed) use exact match 4B locator based lookup in the v6
> packets to get from segment end to segment end.
>
> On the other hand your comments about greatness of MPLS ... simplified
> data plane and depending on the hardware difference in jitter (in sub ms
> ranges - if that even matters) comes up with a lot of control plane
> complexity when you want to build a network across all continents, yet keep
> it scoped from IGP to areas or levels. No summarization in MPLS in FECs is
> something we should not sweep under the carpet.
>
>
> I found multi-level IS-IS to be useless in an MPLS network because you
> still need to leak routes between L2 and L1 in order to form MPLS FEC's. So
> you simplify the network by having a single L2 (or just Area 0 in OSPF),
> because today's control planes can handle it. And yes, some are brave
> enough to run RFC 3107 if it becomes a problem, but if you can afford to
> string a network together across all continents, I doubt an x86-based
> control plane with 64GB of RAM is topping the list of your problems.
>
> Mark.
>