Re: Evaluation: draft-ietf-pilc-link-design - Advice for InternetSubnetwork Designers to BCP

[Harald Tveit Alvestrand <harald@alvestrand.no>]

Ignoring the specifics of your message and what to do with the specific 
document.....

the basic problem seems to be that if you have

IP router --------- IP router -------- IP router
          --------- IP router --------

on the physical layer (middle routers are layer 2 and layer 3 devices), and 
the subnet technology forces you to act as if you had

IP router ---- Cloud
IP router ---- where all hops
IP router ---- look the same
IP router ----

then IP routing will not be optimal, either in terms of resource usage
or in terms of convergence time and amount of state kept.

the cloud is presumably implemented because one wants other services to run 
across it, so just converting the links to IP-over-foo is not an option.

seems to me one viable design approach would be to allow IP to limit its 
usage of the subnet technology to the hops that have real simple physical 
mappings - much as one used to manually configure ATM PVCs that followed 
the fiber ducts while there was still thought to be a potential market for 
non-IP use of ATM.

the general issue used to be ROLC once upon a time. For a while I thought 
it had transmogrified into CCAMP.

But it's one of those architectural issues that doesn't seem to go away.

            Harald