Security review of Explicit Congestion Notification (ECN) Experimentation draft-ietf-tsvwg-ecn-experimentation-05 Do not be alarmed. I have reviewed this document as part of the security directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written primarily for the benefit of the security area directors. Document editors and WG chairs should treat these comments just like any other last call comments. This document liberalizes the ways in which experiments can be conducted on explicit congestion notification with TCP, RTP, and DCCP. Other than the alarming statement: "... this memo places the responsibility for not breaking Internet congestion control on the experiments and the experimenters who propose them, as specified in Section 4.4." there are no security considerations that occur to me. I realize that people experiment with TCP modifications all the time, and the ECN experiments can provide valuable engineering information. Nonetheless, it seems that some higher standard of safety could be in order for today's Internet. But that is outside the scope of this document. Hilarie