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

[David Prall]

Livio,
Where are you getting out of order packets? You do have asymmetric hop
counts, which most likely means asymmetric latency. But all the packets
should be in order. Could use DWDM so that each router isn't directly
connected and everything looks the same number of hops away, of course more
ports are required at the Area 10 edge.

You can use prefix-suppression to only advertise the loopback using OSPF, to
minimize the number of LSA's. Then use MPLS and BGP for all packet
forwarding, including the global table.

David

--
http://dcp.dcptech.com


> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Livio Zanol Puppim
> Sent: Tuesday, October 18, 2011 9:34 PM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] MPLS - MP-BPG with multiple OSPF areas
> 
> 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=0B4Hf34G524HsNTA3ZTc1NTItNmJlNi00ZDQyLW
> I1ZDAtYTg5MTliODRjMDhk&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?
> 
> --
> []'s
> 
> Lívio Zanol Puppim
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