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. Overview: Loosely, this document describes a way of pre-congestion notification marking of packets that builds on the Explicit Congestion Notification (RFC 3168). The marking is only carrying meaning within a given PCN domain. Comments: With the caveat of not being an expert in the field this draft is about, I find the document relatively straightforward to understand and the Security Considerations section reasonably complete (although it perhaps would have been useful to describe what problems that possibly could occur should a party inject PCN-marked packets inside a network?). Editorial: Maybe useful to add a brief early section providing definitions of abbreviations? -- Magnus