Negotiation-based Routing

Interdomain route selection is a complex process driven by constraints arising from topology, policy (e.g., commercial relationships), traffic engineering (e.g., load balancing), and performance. BGP was designed to find (a single) policy conformant route through the network for each source, destination pair. There are two fundamental problems with the route selection process of BGP. First, edge ISPs have too few options for selecting routes. Their choices are limited to the paths selected by their provider(s). As a result, there are many valid paths in the topology that cannot be used. Customers suffer when their providers select poor (from the customer’s perspective) routes, for instance, when the performance metrics for the provider and customer are different. This shortcoming is evident in trends such as increased multi-homing and the use of “intelligent routing” solutions such as those provided by RouteScience. The second problem, which is at the other extreme, is that the senders unilaterally select routes from those available to them. This ignores the traffic engineering needs of the destination and intermediate ISPs. We use the term traffic engineering to loosely refer to the process of controlling the paths through the network (driven by a high-level goal such as efficient use of the network). As a result of this route selection methodology, the destination ISP has no control over which of its upstreams gets used. Similarly, intermediate ISPs have no control over whether the upstream ISP would use the exported route, and if yes, for how much traffic. Over time hooks such as MEDs, communities, and extended communities have been added to the protocol to address this shortcoming. However, these hooks are both insufficient (e.g., ISPs have limited control over incoming paths) and have an unpredictable impact (e.g., MEDs can lead to persistent oscillations [4]). The solution to the first problem is to give more routing choices to the edge ISPs. The solution to the second problem is getting the intermediate and destinations ISPs involved in the route selection process such that the selected route suites all the ISPs. This route negotiation should be explicit and transparent, and its outcome predictable. Otherwise, the result may be a situation much like the current world in which ISPs try to manipulate the outcome to their benefit by trying to second-guess the actions of others. It is important to address both the problems together. Solving only the first exacerbates the second problem – it would be even harder for downstream ISPs to manage and provision their network, and may also have an impact on the overall stability of the Internet. Similarly, solving only the second exacerbates the first by further limiting the choices at the source ISP (downstream ISPs can reject certain routes).