Contra: A Programmable System for Performance-aware Routing


Kuo-Feng Hsu, Rice University; Ryan Beckett, Microsoft Research; Ang Chen, Rice University; Jennifer Rexford, Praveen Tammana, and David Walker, Princeton University


We present Contra, a system for performance-aware routing that can adapt to traffic changes at hardware speeds. While point solutions exist for a fixed topology (e.g., a Fattree) with a fixed routing policy (e.g., use least utilized paths), Contra can operate seamlessly over any network topology and a wide variety of sophisticated routing policies. Users of Contra write network-wide policies that rank network paths given their current performance. A compiler then analyzes such policies in conjunction with the network topology and decomposes them into switch-local P4 programs, which collectively implement a new, specialized distance-vector protocol. This protocol generates compact probes that traverse the network, gathering path metrics to optimize for the user policy dynamically. Switches respond to changing network conditions by routing flowlets along the best policy-compliant paths. Our experiments show that Contra scales to large networks, and that in terms of flow completion times, it is competitive with hand-crafted systems that have been customized for specific topologies and policies.

NSDI '20 Open Access Sponsored by NetApp

Open Access Media

USENIX is committed to Open Access to the research presented at our events. Papers and proceedings are freely available to everyone once the event begins. Any video, audio, and/or slides that are posted after the event are also free and open to everyone. Support USENIX and our commitment to Open Access.

@inproceedings {246500,
author = {Kuo-Feng Hsu and Ryan Beckett and Ang Chen and Jennifer Rexford and David Walker},
title = {Contra: A Programmable System for Performance-aware Routing },
booktitle = {17th USENIX Symposium on Networked Systems Design and Implementation (NSDI 20)},
year = {2020},
isbn = {978-1-939133-13-7},
address = {Santa Clara, CA},
pages = {701--721},
url = {},
publisher = {USENIX Association},
month = feb,

Presentation Video