Introduction to LISP
I’ve been mentioning LISP several times during the last months. It seems to be the only viable solution to the global IP routing table explosion. All other proposals require modifying layers above IP and while that’s where the problem should have been solved, expecting those layers to change any time soon is like waiting for Godot.
If you’re interested in LISP, start with the introduction to LISP I wrote for Search Telecom, continue with the LISP tutorial from NANOG 45 and (for the grand finale) listen to three Google Talks from Dino (almost four hours).
Since LISP-ALT uses IPv4 in EID space, it has to enforce strict aggregation to prevent the same explosion problems we have now with IPv4/IPv6 addressing. While this does not affect multihoming (due to RLOC/EID split), it definitely makes operations more difficult as advanced coordination is required to properly allocate address space and enforce aggregation.
LISP solves just the problem of the core routers' TCAM explosion, nothing else.
However, to me, the forwarding state problem has been highly exagerrated :) After all, TCAM exhaustion was a good driver for buying new hardware and hence made sense for everyone (vendors making new equipment, SPs growring budgest and shifting costs to their customers, etc)
Facebook's or Google's edge devices will have "interesting" forwarding caches :-P
BTW, you cannot defragment EID space. Each /24 (today) or /64 (tomorrow) that wants to be multihomed needs a dedicated entry with two RLOCs.