Re: [RRG] Opportunistic Topological Aggregation in the RIB->FIB Calculation?

[Jari Arkko <jari.arkko@piuha.net>]

I second what Lixia said.

In general, there are plenty of ways to optimize and compress FIB 
tables, some without changing the end result and some that do change the 
routing (Paul Francis' scheme, for instance). I have not reviewed your 
scheme in detail, but if you search you will find others. Some earlier 
discussion here: 
http://www.ietf.org/mail-archive/web/ram/current/msg00567.html
I view the former class (schemes that do not change forwarding 
decisions) as implementation techniques. On a given platform,  you may 
decide that its reasonable to spend some central CPU time to reduce the 
amount of memory needed on the line cards. Of course, there are 
trade-offs, you cannot determine with certainty that compression will be 
effective on today's RIB even if it was very useful on yesterday's, etc. 
My personal opinion is that these techniques should belong to the 
toolkit for people building routers, perhaps more so than they are 
today. Of course there are many other things in the toolkit as well.
I view the latter (Francis-type) schemes as mostly operational 
techniques that can be useful if and when existing equipment on a given 
operator is otherwise unable to deal with the situation. Note that there 
is a trade-off between buying newer equipment vs. operational effort. I 
would like to see Paul's scheme or something else documented at least.
However, our task in the RRG is not really about these types of 
approaches. We should assume they are being applied (I certainly hope 
so) where needed, and it may be useful for the group to understand that 
such techniques exist. But our task should really be about architectural 
change, something that could yield 10x to 1000x difference in table sizes.
Jari


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