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Re: [RRG] some musings on PI v. PA, and assumptions, requirements, and tradeoffs



Haven't we been round this particular mulberry bush a few times already? Yes, the routing system offers the path of least resistance when attempting to solve a number of issues, and thats because routing solutions are invariable simple and (today) cheap. And the Loc/ID split seems to be a pretty massive solution for something that does not appear to be a commonly accepted problem in the first place. So yes, we continue to use the routing system for multi-homing, traffic engineering and similar. It just works.

To connect to stationary hosts yes. But if they are moving around and keep their addresses regardless if those addresses are from PI or PA space, then location needs to be topological. Furthermore, moving around a lot and injecting and withdrawing more specifics is just going to add churn in a major way.

The only concern I've heard voiced that seems to me to be a real issue in all this is the question "what if we all did that?" Are there numbers for "we all" that appear to be beyond the capability of the technology curve? Are there numbers for "we all" that might even be beyond the capability of the protocol? If so, then we probably need some

All valid questions with no magic answers. But if we are concerned with churn and convergence of control-plane tables into forward-plane tables and looking at 10^6 sites plus the mobility aspect, the numbers are getting large. But this is not scientific but just gut feel.

kind of plan B, and it does appear to me that if you want to get out of the tyranny of incrementalism then you need to consider something a little more fundamental in terms of network architectures when you start to look at what would make a Plan B effective. For me this path is where the split loc/ID approaches start to gain traction. But to be clear, the split loc/ID approach does not appear to me to be a viable tactical response to routing inflation in the near term future.

As I have said before Geoff, solving the routing table size problem is just a side benefit if we first solve the "non-search-site" multihoming problem. That is to allow them to use both of their links (I believe you said that 80% of all multi-homed sites have exactly 2 connections) and to be able to tell hosts returning packets to them which link to use and how to failover.

A level of indirection can solve this but the big question is it too much of a solution. That is, do we have the guts to just brute-force and continue to send in PI prefixes.

Dino

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