A Fast-Convergence Routing of the Hot-Potato

TL;DR

The paper introduces OPTIC, a method that accelerates hot-potato routing convergence by precomputing gateway sets, significantly reducing BGP updates and maintaining optimal transit traffic routing after IGP changes.

Contribution

OPTIC provides a novel pre-computation approach that ensures rapid BGP route updates post-IGP events without losing the hot-potato property, reducing update complexity.

Findings

Reduces BGP entry counts by up to 99% in stub networks.

Enables near-instantaneous route updates after IGP convergence.

Scales linearly with the number of gateway groups.

Abstract

Interactions between the intra- and inter-domain routing protocols received little attention despite playing an important role in forwarding transit traffic. More precisely, by default, IGP distances are taken into account by BGP to select the closest exit gateway for the transit traffic (hot-potato routing). Upon an IGP update, the new best gateway may change and should be updated through the (full) re-convergence of BGP, causing superfluous BGP processing and updates in many cases. We propose OPTIC (Optimal Protection Technique for Inter-intra domain Convergence), an efficient way to assemble both protocols without losing the hot-potato property. OPTIC pre-computes sets of gateways (BGP next-hops) shared by groups of prefixes. Such sets are guaranteed to contain the post-convergence gateway after any single IGP event for the grouped prefixes. The new optimal exits can be found through a single walk-through of each set, allowing the transit traffic to benefit from optimal BGP routes almost as soon as the IGP converges. Compared to vanilla BGP, OPTIC's structures allow it to consider a reduced number of entries: this number can be reduced by 99\% for stub networks. The update of OPTIC's structures, which is not required as long as border routers remain at least bi-connected, scales linearly in time with its number of groups.