11 - Separating routing policy from mechanism in the network layer

Summary

Introduction

Despite the world-changing success of the Internet, shortcomings in its routing and forwarding system (i.e., the network layer) have become increasingly apparent. One symptom is an escalating “arms race” between users and providers: providers understandably want to control use of their infrastructure; users understandably want to maximize the utility of the best-effort connectivity that providers offer. The result is a growing accretion of hacks, layering violations and redundant overlay infrastructures, each intended to help one side or the other achieve its policies and service goals.

Consider the growing number of overlay networks being deployed by users. Many of these overlays are designed specifically to support network layer services that cannot be supported (well) by the current network layer. Examples include resilient overlays that route packets over multiple paths to withstand link failures, distributed hash table overlays that route packets to locations represented by the hash of some value, multicast and content distribution overlays that give users greater control of group membership and distribution trees, and other overlay services. In many of these examples, there is a “tussle” between users and providers over how packets will be routed and processed. By creating an overlay network, users are able to, in a sense, impose their own routing policies – possibly violating those of the provider – by implementing a “stealth” relay service.

The lack of support for flexible business relationships and policies is another problem area for the current network layer.