in defense of lisp (was: Anybody can participate in the IETF)

Wed Jul 13 17:28:04 UTC 2011

On Jul 13, 2011, at 12:02 PM, Ronald Bonica wrote:

> At this point, it might be interesting to do the following:
> 
> - enumerate the operational problems solved by LISP
> - enumerate the subset of those problems also solved by RFC 6296
> - execute a cost/benefit analysis on both solutions

I'll let a LISP advocate state the values of LISP. My perception: it's a lot of overhead for what you actually get, comparable to building what Cisco once called "fast switching" into the network.

In looking at 6296, I was trying to find a way to make edge networks be willing to use PA addresses instead of PI. If you have one ISP and never want to change ISPs, PA is wonderful; if you have multiple ISPs, the prevailing multihoming model in the IETF calls for you to have a subnet from each of your upstream prefixes on each LAN and to have your host divine which address pair implies the most acceptable route to your destination. If you have any ISP's prefix on your LAN and you want to remove the ISP (change to a different one, stop using one, whatever), you are somehow buried in renumbering (See RFC 4192). Edge networks are not crazy about renumbering, and they're not crazy about having a prefix per ISP on each LAN - hence PI. So, to get edge networks to use PA addresses, I reason that the edge network needs an address that is not derived from its upstream, and it has to be translated to the prefix of the upstream. The other factor (how to not require a change to TCP/UDP checksums) is the checksum update.

So to my way of thinking, NPTv6 provides a way to statelessly (e.g. scalably) enable any host to talk with any host and at the same time make the edge network look PA to the upstream, has the managability characteristics of PI in the edge network, and not have to change TCP/UDP.

LISP, to my knowledge, provides no way to push back on route table growth (it moves it from the transit network to the edge network, but the edge network still has to deal with it).

To my mind, if you liked stateful NAT in IPv4, you'll like stateless NPTv6 in IPv6 better.

With that, I'll return you to your more operational musings. I'm with the IETF. Please feel free to inform the world on how clueless I am operationally. I'm already convinced of the fact; that's why I talk with and listen to operators.