WAN Routing in Data Centers with Layer-2 DCI

A while ago I got an interesting question:

Let's say that due to circumstances outside of your control, you must have stretched data center subnets... What is the best method to get these subnets into OSPF? Should they share a common area at each data center or should each data center utilize a separate area for the same subnet?

Assuming someone hasn’t sprinkled the application willy-nilly across the two data centers, it’s best if the data center edge routers advertise subnets used by the applications as type-2 external routes, ensuring one data center is always the primary entry point for a specific subnet. Getting the same results with BGP routing in Internet is a much tougher challenge.


  1. Have you ever tried G8032?
    1. Doesn't help much unless you have your own dark fiber (or lambdas, I guess) ... and it definitely won't save the day if you lose all paths in the DCI link.
    2. Carrier Ethernet should be available in most first world countries?
    3. G.8032 is simply a L2 redundancy protocol and won't solve anything with regards to the IP layer and worrying about proper routing design.
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