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A few weeks ago, Daniel posted a piece about using different underlay and overlay protocols in a data center fabric. He says:
There is nothing wrong with running BGP in the overlay but I oppose to the argument of it being simpler.
One of the major problems we often face in network engineering—and engineering more broadly—is confusing that which is simple with that which has lower complexity. Simpler things are not always less complex. Let me give you a few examples, all of which are going to be controversial.
When OSPF was first created, it was designed to be a simpler and more efficient form of IS-IS. Instead of using TLVs to encode data, OSPF used fixed-length fields. To process the contents of a TLV, you need to build a case/switch construction where each possible type a separate bit of code. You must count off the correct length for the type of data, or (worse) read a length field and count out where you are in the stream.
Fixed-length fields are just much easier to process. You build a structure matching the layout of the fixed-length fields in memory, then point this structure at the packet contents in-memory. From there, Continue reading