[c-nsp] Unified MPLS - Discrete area or separate IGP in Access Layer

Pshem Kowalczyk pshem.k at gmail.com
Thu Feb 6 16:51:50 EST 2014


In our case (national network + regional metros, that split into
multiple 'areas') we initially deployed 2 levels of ISIS. What we
discovered that if a single 'core' node has to provide connectivity to
multiple 'access' areas the L1 area becomes continuous and spills the
routes (ISIS doesn't have a separate database per area like OSPF, only
one per level). Since we have asr901s in those access domains and
provide 'fast re-convergence' we have to keep the size of the routing
table in individual access domain minimal. As a result - we moved to
ISIS L2 on the core and separate OSPF process for each 'access'
domain, with different areas for each access domain. We keep the areas
as total stubs and filter out the default route on each router. We
could use a separate ISIS process for each access domain but decided
that it would be more complicated that way.

kind regards

On 7 February 2014 03:36, Adam Vitkovsky <adam.vitkovsky at swan.sk> wrote:
> Hi Folks,
> This is regarding Unified MPLS for LTE aka Hierarchical MPLS with RFC3107.
> I'd like to know whether there are networks out there running separate IGP
> processes per each access or aggregation network.
> Or whether you are running common IGP and using separate area/level for each
> aggregation/access network please?
> I'm interested for any pros/cons either of these solutions have.
> I guess it's no biggie whether there are going to be separate processes in
> access and core not talking to each other or just separate areas.
> Thank you very much.
> adam
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