  We present ez-Segway, a decentralized mechanism to consistently and quickly
update the network state while preventing forwarding anomalies (loops and
black-holes) and avoiding link congestion. In our design, the centralized SDN
controller only pre-computes information needed by the switches during the
update execution. This information is distributed to the switches, which use
partial knowledge and direct message passing to efficiently realize the update.
This separation of concerns has the key benefit of improving update performance
as the communication and computation bottlenecks at the controller are removed.
Our evaluations via network emulations and large-scale simulations demonstrate
the efficiency of ez-Segway, which compared to a centralized approach, improves
network update times by up to 45% and 57% at the median and the 99th
percentile, respectively. A deployment of a system prototype in a real OpenFlow
switch and an implementation in P4 demonstrate the feasibility and low overhead
of implementing simple network update functionality within switches.
