[c-nsp] MPLS - MP-BPG with multiple OSPF areas

[Livio Zanol Puppim]

Hello everybody,

I have a doubt with a lab design that we are creating to test some MPLS
topologies. I would like to know if anybody can help me solve a problem that
I am facing about routing paths. To help ilustrate the topology I'm sending
the image link below.

https://docs.google.com/leaf?id=0B4Hf34G524HsNTA3ZTc1NTItNmJlNi00ZDQyLWI1ZDAtYTg5MTliODRjMDhk&hl=en_US

In the topology, I have two core routers interconnected with a 1 Gbps link
and several other routers interconnected with a 100Mbps link. The interfaces
between the core routers are in the OSPF area 0 and all other physical
interfaces are in the OSPF area 10. Each one of the two core routers also
have a connection to the area 10 using a 100Mbps interface.

The router ID and the "update-source interface", on the core routers (PE1)
is a loopback interface that belongs to the OSPF area 0.
The router ID and the "update-source interface", on the access routers (PE6)
is a loopback interface that belongs to the OSPF area 10.

After establishing OSPF adjacencies between all routers, the BGP process
starts to establish connection, and this undesirable behavior happens:

When the router PE1 (area 0) wants to establish a BGP session with router
PE6 (area 10), the packet flow through all 100Mbps (purple arrow). When the
router PE6 (area 10) responds, the packet flow through the 1Gbps connection
between the core routers (red arrow). Every flow that needs to use the LSPs
will do logically the same, causing out-of-order packets at the network.

I know that this is an expected behavior, as intra-area routes are preferred
over inter-area routes, no matter what the link cost is.

The question is: What solution do you guys think it's better for this
scenario, so that the packet flow goes always through the optimal path?
- Sham-links;
- Extended area 0 to one more hop;
- Change the "update-source interface" for area 10;
- Create small areas between the core and access routers
- Other solutions...

We are planning to deploy a network with more than 200 PE routers in a
similar scenario, and I don't think that a single OSPF area is a good choice
for us.

Can anybody help with some advice?

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Lívio Zanol Puppim