  In this work, we propose a radical, incrementally-deployable Internet routing
paradigm in which the control plane of multiple networks is centralized. This
follows the Software Defined Networking (SDN) paradigm, although at the
inter-domain level involving multiple Autonomous Systems (AS). Multi-domain SDN
centralization can be realized by outsourcing routing functions to an external
contractor, which provides inter-domain routing services facilitated through a
multi-AS network controller. The proposed model promises to become a vehicle
for evolving BGP and uses the bird's eye view over several networks to benefit
aspects of inter-domain routing, such as convergence properties, policy
conflict resolution, inter-domain troubleshooting, and collaborative security.
In addition to the proposed paradigm, we introduce a publicly available
emulation platform built on top of Mininet and the Quagga routing software, for
experimenting in hybrid BGP-SDN AS-level networks. As a proof of concept we
focus specifically on exploiting multi-domain centralization to improve BGP's
slow convergence. We build and make publicly available a first multi-AS
controller tailored to this use case and demonstrate experimentally that SDN
centralization helps to linearly reduce BGP convergence times and churn rates
with expanding SDN deployments.
