The high level summary is that draft-mm-wg-effect-encrypt version 13 is significantly improved from previous versions, but that the document would benefit a lot from additional work. I am not convinced that the sections on data center and enterprises belong in this specific document - they seem too high level to bring serious information to readers. Maybe stage a separate document to survey enterprise issues in some depth? I also feel that section 7 is way too speculative for a survey document. I have been using the "side by side" feature of the IETF web site to compare the last draft that I reviewed (draft 10) and the current draft (draft 13). That tools shows the high volume of changes and reorganization that happens between these two versions. These changes generally make the document more balanced, and that's a welcomed development. There are however many places where I find that the documents lists controversial techniques without sufficient caveats. I will list some of them in the reminder of this review. The introduction and the summary have been rewritten to clearly place the document in perspective. The previous versions could be read as a plea to stop encrypting traffic so previous management practices could continue. The new introduction makes clear that the IETF needs to prevent pervasive monitoring and improve the users' privacy, and that the goal of the document is to list areas in which current management practice need to evolve, or areas where substitute practices have to be found. I also appreciate the note that "some of (current management practices) have been considered controversial from a technical or business perspective or contradictory to previous IETF statements" -- and the implicit implication that the IETF will not attempt to restore all of these. 2. Network Service Provider Monitoring Section 2, "Network Service Provider Monitoring", has been reorganized to focus on management goals rather than simply provide a list of existing management tools. The description of the trouble shooting tasks in section 2.2 is useful. It makes the point that "application server operators using increased encryption should expect to be called upon more frequently to assist with debugging and troubleshooting", and that could lead to some interesting work in the IETF. There is paragraph at the end of section 2.1.2, Troubleshooting, that states that "the push for encryption by application providers has been motivated by the application of the described techniques." I think that paragraph is misplaced. As far as I can tell, the application providers are first concerned with "content management" techniques that modify the data stream. Any change of content has the potential to generate bugs that are difficult for the application provider to fix. The second concern is "ossification", when traffic characterization based on inferred features of the application traffic leads to adverse consequences when the application or transport protocols evolve. Neither of those is directly relevant to the "troubleshooting" task. Maybe move that paragraph higher in the document, e.g. in the introduction of section 2? If not that, then maybe move it to section 2.2.2, since one purpose of application encryption is indeed to defeat differential treatment in the network. I find the discussion of load balancers in section 2.2.1 somewhat confusing. It seems to cover three functions: load balancers in data centers, load balancers integrated with the network, and a network management function that tries to maintain proper connectivity to anycast addresses services in the presence of mobility. It might be useful to move the discussion of "classic" load balancers to section 3, and to discuss the problem of anycast continuity in a separate subsection. The anycast discussion seems to assume that the network operator alone has to deal with the supposed inadequacies of the application providers. It seems obvious that this problem would be much better solved by improved handling of mobility in content distribution networks, rather than by some complex machinery in the network itself. This might need to be stated. Section 2.2.2 on Deep Packet Inspection could state that it is very often possible to classify traffic based on analysis of the encrypted data. Audio stream, video streams and web traffic have very different signatures, even when encrypted. At the same time, it should also note that many application providers are actively working to defeat the "unilateral" traffic classification enabled by these techniques, complementing encryption with various techniques like multiplexing or padding. We could well observe an arms race between more powerful network based analysis and smarter application hiding. The discussion of performance enhancing proxies in section 2.2.3 states that "This optimization at network edges measurably improves real-time transmission over long delay Internet paths or networks with large capacity-variation (such as mobile/cellular networks)." This is not a consensual statement. Operators do indeed hope that deploying such proxies will improve performance, but independent measurements have shown that such proxies often in fact degrade performance. The studies that show improvement tend to be based on old network technologies, or on ancient TCP stacks. If the authors want to keep a statement like that, they should add references to actual measurements. At a minimum, the text should note that many application providers disagree with the assessment presented here, and that the development of encrypted transports such as QUIC is largely motivated by the desire to mitigate the negative effects of such "performance-dehancing" proxies. The discussion of caching in section 2.2.5 correctly states the tension between network usage and application control. It could also state the inherent privacy risk associated with network based caches: they will provide a log of which users accessed what cached content. There is a reference to draft-thomson-http-bc-01, but as far as I know the authors have abandoned it, in part because they could not solve the related privacy issues. In any case, that draft expired several month ago, and the reference is probably not appropriate. In section 2.3.3, Application Layer Gateways, I was wishing it would say something about IPv6. But then of course most IPv6 deployments today involve a form of NAT64... Section 2.3.4 documents the "HTTP Header Insertion" technique. The relation between that technique and "Network Service Provider Monitoring" is unclear -- header insertion is certainly not a network monitoring tool. It is also a highly controversial tool, as documented for example in https://www.theverge.com/2016/3/7/11173010/verizon-supercookie-fine-1-3-million-fcc. I wonder whether it is appropriate to describe this at all in a document dedicated to network management, and my simple suggestion would be to just remove that section altogether. Failing that, the text needs to be modified to note the controversial nature of the process, and its impact on privacy. The authors could also note that the function could be trivially implemented in the client's browsers if it was really needed and approved by the users. There is no technical need to have anything like that "in the network". 3. Encryption in Hosting SP Environments After examining network monitoring in section 2, the draft continues with an analysis of "Hosting SP Environments" in section 3, and section 4 describes "Encryption for Enterprises". I assume that the initials SP stand for "Service Provider" -- spelling it out would not hurt. I really wonder whether these sections belong in the document at all, rather than being published in separate documents. "Hosting Service Provider Environments" appears to be a subset of the general "Data Center" problem. It is true that some network providers also provide data center services for their customers, but these network providers represent only a small fraction of the service hosting industry. Similarly, some network providers provide services to enterprises, but there is a wide variety of enterprises. It is hard to believe that the authors of an individual draft have authority to speak at the same time about network services, data centers, and enterprises. In my opinion, it would be simpler to just excise section 3 and 4 from this draft, and use the content as input for specific drafts describing issues in data centers and enterprises. In any case, I am puzzled by the reference to Data Loss Prevention (DLP) in the introduction of section 3.1. Data exfiltration is indeed a security issue, but I knew it primarily as an issue in enterprise networks. It does indeed become an issue in data centers when an enterprise application is hosted outside the data center, but it is a bit strange to see the first reference there. I already suggested to move section 3 and 4 out to a different document. Failing that, I would suggest reversing the order of section 3 and 4, i.e., discuss enterprise issues first and data center issues next. The discussion of Customer Access Monitoring in section 3.1.1 is a bit strange. Most applications control customer access based on the customer identity, not based on the IP addresses of the customer -- the whole point of the "cloud" is that applications can be accessed from anywhere. Some applications do perform additional checks, mainly as a defense against stolen credentials, and would attempt to block access if the network location does not look plausible for this specific user. These are useful techniques, but the relation with encryption of data is somewhat thin. It seems to reinforce my point that data center issues would best be discussed in a separate document. The reminder of section 3 appears to be a high level tutorial on the operation of data centers. It is not clear that there is a particular problem with encryption there. Indeed, I note that a lot of operators of big data centers, such as for example AWS, Azure or Google, have voluntarily pushed for increased used of encryption. I don't learn much by reading these sections, and I question whether they belong in the draft. 4. Encryption for Enterprises The discussion on encryption in enterprises would probably benefit from input by a variety of enterprise network managers. I found the discussion somewhat hard to read. It seems that the authors want to tackle three issues: the enterprise as a target for security attacks, the enterprise as an application provider, and the enterprise as a network provider. These are discussed in sections 4.1.1, 4.1.2, and 4.1.3. The description of attacks in 4.1.1 is somewhat high level. It starts from the statement that "A significant portion of malware hides its activity within TLS or other encrypted protocols" to draw a requirement to monitor encrypted traffic, when in practice there are many other monitoring points, from endpoint monitoring to data base activity logs to logs at network authentication servers -- as stated in the last paragraph of the section. The monitoring of application performance in enterprises appears strangely focused on the "IPv6 Destination Option Header (DOH) implementation of Performance and Diagnostic Metrics (PDM)". I understand that most big applications solve their monitoring need by implementing some form of telemetry, which is not affected at all by encryption, yet I see no mention of this telemetry approach in the discussion. I had a hard time reading section 4.1.3, Enterprise Network Diagnostics and Troubleshooting. It seems to cover a variety of techniques meant to monitor application services without actually instrumenting the application, and as such is not very convincing. The meat of section 4 appears to be in section 4.2, which is covering the issue of data loss prevention, and generally detection of data exfiltration. Again, this is an issue that would be worth a specialized draft. 5. Security Monitoring for Specific Attack Types Looks fine, and this review is already very long. 6. Application-based Flow Information Visible to a Network Do we need this section at all? It seems that most of the information could be captured by adding a small subsection to 2.1. Passive Monitoring. 7. Impact on Mobility Network Optimizations and New Services This section appears to be a mix of replication of statements already made in section 2, and some speculation on the effect of transport header encryption, such as deployed in Web RTC (SCTP over DTLS) or planned in QUIC. There are active discussions in the QUIC WG to provide alternative to transport header inspection for RTT monitoring, and possibly also for packet loss monitoring. Contrarily to the rest of the document, this section seems speculative in nature. It discusses the possible effects of transport header encryption on the possible deployment of new services, which do not appear to be based on any IETF standard. I think the document would be stronger if some of the content of section 7 was moved to the appropriate part of section 2, and if the speculative statements were published as a separate document. 8. Response to Increased Encryption and Looking Forward Looks reasonable. -- Christian Huitema