In the referenced message, Stephen Stuart said:
I can't really see why, as long as the provider has punched the appropriate hole for your aggregate in their filters. More specific routes always win out. Or am I missing your point?
The point, I think, is the effort involved in using global route announcements to solve your traffic engineering problems.
When you use provider-assigned space, you have to coordinate your intent to add entries to the global routing table with the provider who assigned the space and the providers that you want to accept the new routes.
When you use provider-independent space, you get to decide to add entries to the global routing table pretty much all by yourself, modulo running afoul of the occasional provider that does not, by default, buy into solving local traffic engineering problems in other people's networks using global routing table entries.
Stephen
Not to mention that the common retort is that everyone else in the world should upgrade their CPU and memory to solve a third parties traffic engineering problem. Thereby transferring the cost to others. The verio (and others) mechanism involves a stated policy soundly derived based upon RiR allocation policy. A policy which, if everyone announced their aggregates would lead to no blackholes during steady-state. If parties feel the need to exchange long prefixes, they can do so privately, without infecting everyone. In fact, many providers exchange regional routes, tagged no-export, for such mutual agreed-upon optimal traffic exchange purposes. This should, however, be constrained to those parties who mutually agree upon it. However, there are some who want to handle their traffic engineering needs preferably by transferring the costs to others. This is just shady, even if it makes perfect "business sense" from a capitalistic "maximize profit no matter what the consequences" mind set. I wonder how the anti-filter folks would feel if all of their providers/peers ceased filtering out iBGP routes on the sessions facing them. Would they begin scrambling to filter? If so, where would the line be drawn? Some arbitrary prefix-length, or based upon a published length obtained from some allocation authority? What about if everyone ceased filtering out their iBGP routes, and just leaked it all? Looking at only a single router, I could add another 8538 prefixes into the routing system. Certainly everyone could handle 9k more prefixes, right? Ok, then we get to do that across all my routers. Then across all providers. This is all in the name of optimal routing, right? What's a couple million routes between friends?