[c-nsp] Seamless MPLS interacting with flat LDP domains

[Robert Raszuk]

Even better to get rid of transport MPLS all together ... There is nothing
in LDP MPLS which would be of any value as compared with basic IP UDP
encap. Of course you can still run all of your L3VPNs or EVPNs if you wish
so over IP transport.

Then you no longer need to carry 1000s of /32s in your IGP or BGP around as
IP has this nice property of summarization.

Putting it all flat (in one IGP) sure is quite doable these days, but it
does not make it immediately a good idea :)

Cheers,
R.

On Mon, Apr 29, 2019 at 3:32 PM <adamv0025 at netconsultings.com> wrote:

> > Igor Sukhomlinov
> > Sent: Friday, April 26, 2019 5:23 AM
> >
> > Hi all,
> >
> > I wonder if anyone has experience with integrating a UMMT/Seamless MPLS
> > domain (BGP-LU running over isolated IGP regions) with an existing flat
> LDP
> > network.
> >
> Yes from well before the term was coined, but that was for the Inter-AS
> setup.
> They used to call it hierarchical MPLS or something along those lines.
>
> > The customer wants to make sure the existing LDP domain is still running
> > while the newer BGP enabled domain is steadily coming online, but what is
> > the best approach to transport the services between the networks?
> >
> First of all hierarchical MPLS is not for everyone so the obvious question
> is do you need to keep the domains separate due to scalability reasons?
> If not then rather than investing time into "Seamless MPLS" project invest
> the time into migrating onto common IGP which will result in a much simpler
> network (IGPs can support huge number of prefixes nowadays and  ISIS/OSPF
> can compute SPF for important prefixes first -and do by default with
> possibility to customize).
>
> If you are doing this to overcome potential scaling issues, which should be
> the only reason for doing this, then the easiest and most scalable approach
> is to leave the individual IGP domains truly separate and have only BGP
> carry the necessary RIDs/PE-loopbacks along with their respective labels
> between PEs and ABRs/ASBRs while forming the second (inter-area/inter-as)
> level of transport labels, which in combination with complete separate
> process of deriving intra-area/intra-as label-stack will produce the
> complete end to end label switch path.
> There's no redistribution involved in this kind of setup (hence no
> pollution
> of local intra-area/intra-as IGP), basically clear separation of concerns
> and all controls or "extras" are kept to the BGP-LU layer.
>
> adam
>
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