WREN 2009, the Workshop on Research on Enterprise Networking, was held on August 21, 2009, in conjunction with SIGCOMM 2009 in Barcelona. WREN focussed on research challenges and results specific to enterprise and data-center networks. Details about the workshop, including the organizers and the papers presented, are at http://conferences.sigcomm.org/ sigcomm/2009/workshops/wren/index.php. Approximately 48 people registered to attend WREN. The workshop was structured to encourage a lot of questions and discussion. To record what was said, four volunteer scribes (Nathan Farrington, Nikhil Handigol, Christoph Mayer, and KokKiong Yap) took notes. This report is a merged and edited version of their notes. Please realize that the result, while presented in the form of quotations, is at best a paraphrasing of what was actually said, and in some cases may be mistaken. Also, some quotes might be mis-attributed, and some discussion has been lost, due to the interactive nature of the workshop. The second instance of WREN will be combined with the Internet Network Management Workshop (INM), in conjunction with NSDI 2010; see http://www.usenix.org/event/ inmwren10/cfp/ for deadlines and additional information. Also note that two papers from WREN were re-published in the January 2010 issue of Computer Communication Review: “Understanding Data Center Traffic Characteristics,” by Theophilus A Benson, Ashok Anand, Aditya Akella, and Ming Zhang, and “Remote Network Labs: An On-Demand Network Cloud for Configuration Testing,” by Huan Liu and Dan Orban. 2. SESSION 1: SECURITY