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After last week’s, a reader left a comment noting “I2RS doesn’t manipulate forwarding data.” If I2RS isn’t “manipulating forwarding data,” then what, precisely, is it doing? I thought it’s worth a post to try and help folks understand the definitions in this space—except, as you’ll soon discover, there are no definitions here. In fact, it’s almost impossible to create a single set of definitions that will clarify the issues involved in understanding the various sorts of state in a network device. The following illustration might be helpful in trying to understand the vagaries of the various kinds of state, and the confusion that results from the various names used in different places.

It would be “nice” to say something like: information held in the forwarding table, that’s actually used to forward traffic through the router, is the only real “forwarding data.” This makes for a nice clean definition that clearly separates, say, what the RIB does and what the FIB does in most of the hardware based switching devices produced today. There are two problems with this clean definition, however.
First, there are, and always will be, devices produced that simply don’t have a forwarding table. Instead of Continue reading