I am the assigned Gen-ART reviewer for this draft. The General Area Review Team (Gen-ART) reviews all IETF documents being processed by the IESG for the IETF Chair.  Please treat these comments just like any other last call comments. For more information, please see the FAQ at . Document: draft-ietf-aqm-fq-codel-05.txt Reviewer: Elwyn Davies Review Date: 2016/03/06 IETF LC End Date: 2016/03/17 IESG Telechat date: (if known)  2016/03/17 Summary: Almost ready.  There are a couple of minor issues that are barely above the level of nits plus a fair bit of editorial work. I notice that the draft is on the IESG agenda on the day that last call ends.  If the authors wish to sort out the nits before the end of last call, I will be happy to work with them on this. Major issues: None. Minor issues: Treatment of packets that don't fit into the hashing classification scheme:  The default FQ-CoDel hashing mechanism uses the protocol/addresses/ports 5-tuple, but there will be packets that don't fit this scheme (especially ICMP).  There is no mention of what the classification would do with these packets.  I guess that one extra queue would probably suffice to hold any such outliers, but it would be wise to say something about how the packets from this/these queue(s) would be treated by the scheduler.  It might also be useful to say something about treatment of outliers in other classification schemes, if only to say that the scheme used needs to think about any such outliers. s6.2, last para:  The proposal to add flow related marking to encapsulated packets needs to come with a very well exposed security and privacy health warning.. [It occurs to me that it might be possible to confine these markings to out of band notifications within the originating host which would allow fq_codel or similar to Flow Queue the packets getting them into a sensible order on the outgoing link.  Once the packets had been ordered in this way, a subsequent box (maybe an ADSL modem or suchlike) linking a home environment to the outside world could work purely on source address, thereby interspersing the packets from different hosts onto the external link but not needing to reorder the packets from each individual host.  Not sure if this is a sensible idea but it looks like a way to avoid the privacy issues.] s11:  Internet Drafts are not scientific papers as such and do not usually have a Conclusions section.  I think it would be useful to move the paragraph in s11 as is to s1.  Since this draft is targeted for Experimental RFC status, it would be useful to suggest (maybe in s7) that experiments along the lines noted in s7 might be carried out and there results reported (where?  AQM WG?).  Given the developments with Cake, I am not sure whether the authors expect this version of FQ-CoDel to make it onto standards track or BCP, but to set out some sort of expected trajectory is desirable. Nits/editorial comments: General: s/i.e./i.e.,/, s/e.g./e.g.,/ Draft Title: The acronym CoDel with an uppercase D is used everywhere else in the document - Suggest the title should be FlowQueue-CoDel Abstract:   Need to expand AQM. [DNS and and CPU are 'well-known' - http://www.rfc-editor.org/materials/abbrev.expansion.txt ] General: It would be helpful to capitalize Quantum throughout (or at least from s3 onwards)  to emphasise that it is a configured value.  Likewise Interval and Target parameters.  Maybe also Flow and Queue as they a defined terms. s1, para 1: It would be helpful to give the full title (FlowQueue-CoDel), expand AQM (again), provide a refernece explaining the term bufferbloat and give references for AQM, basic CoDel, DRR and the ns2/ns3 network simulators. I would think one or both of the following would be useful (long term stable) refs for bufferbloat (the first is useful because the article is publically available rather than needing a sub to IEEE or ACM): Jim Gettys. 2011. Bufferbloat: Dark buffers in the Internet. IEEE Internet Comput. 15, 3 (2011), 95–96. DOI: http://dx.doi.org/10.1109/MIC.2011.56 (freely available at http://www.bufferbloat.net/attachments/27/IC-15-03-Backspace.pdf ) and/or Jim Gettys and Kathleen Nichols. 2012. Bufferbloat:Dark buffers in the Internet. Commun. ACM 55, 1 (2012), 1–15. DOI: http://dx.doi.org/10.1145/2063176.2063196 Suggest: OLD:    The FQ-CoDel algorithm is a combined packet scheduler and AQM    developed as part of the bufferbloat-fighting community effort.  It    is based on a modified Deficit Round Robin (DRR) queue scheduler,    with the CoDel AQM algorithm operating on each queue.  This document    describes the combined algorithm; reference implementations are    available for ns2 and ns3 and it is included in the mainline Linux    kernel as the fq_codel queueing discipline. NEW:    The FlowQueue-CoDel (FQ-CoDel) algorithm is a combined packet scheduler and    Active Queue Management (AQM) [RFC 3168] algorithm    developed as part of the bufferbloat-fighting community effort (see http://www.bufferbloat.net ).  It    is based on a modified Deficit Round Robin (DRR) queue scheduler [DRR][DRRPP],    with the CoDel AQM algorithm operating on each queue.  This document    describes the combined algorithm; reference implementations are    available for the ns2 ( http://nsnam.sourceforge.net/wiki ) and    ns3 ( https://www.nsnam.org/wiki ) network simulators, and it is    included in the mainline Linux kernel as the fq_codel queueing discipline. END s1.2, definition of Flow: s/protocol/protocol number/; also mac is ambiguous - s/mac address/media access control (MAC) address/ s1.2, definitions of Flow and Queue: To make the mentions of hash in the definition of Queue comprehensible, it would be sensible to mention 'hash' in the definition of flow.  Suggest adding:     The identifier(s) of a flow are mapped to a hash code used internally in FQ-CoDel to organize the packets into Queues. s1.2: Probably worthwhile adding the references for CoDel and DRR to the definitions. s1.2: It would help with subsequent understanding to provide definitions of the Interval and Target parameters of the CoD el scheme.  Suggest: ADD: Interval: Characteristic time period used by the control loop of CoDel to age the value of the minimum sojourn time of packets in a Queue (i.e., the time spent by the packet in the local Queue) that is used to indicate when a persistent Queue is developing (see Section 4.3 of [CODELDRAFT]). Target: Setpoint value of the minimum sojourn time of packets in a Queue used as the target of the control loop in CoDel (see Section 4.4 of [CODELDRAFT]). END s1.3, para 1: It would be helpful to expand SQF: s/SQF/Shortest Queue First (SQF)/ s1.3, para 1: s/differently than/differently from/ (the latter is good for both US and British English) s1.3, para 2: Suggest starting the para with 'By default,' so that the 'although' bit is not a surprise. s1.3, para 2:  Adding a reference for the CoDel algorithm would help.  In particular, linking to http://queue.acm.org/appendices/codel.html as well as the basic article would be helpful - I am not sure if the CoDel article is available for free to all but the appendix seems to be. s1.3, para 4: s/current implementation/Linux implementation at the time of writing/  s1.3, para 5: s/rather than a packet-based./rather than packet-based./ s1.3, para 6 (next to last para): However, in practice many things that are beneficial to have prioritised for typical internet use (ACKs, DNS lookups, interactive SSH, HTTP requests, ARP, RA, ICMP, VoIP) _tend_ to fall in this category, which is why FQ-CoDel performs so well for many practical applications. I am doubtful as whether mentioning ARP, RA and ICMP in this statement is appropriate since they don't fit into the default flow classification scheme, and are not really flows as such.  As mentioned in Minor Issues above some discussion of non-flow packets is needed IMO.  They could be left out here without problem I think. s3.1, para 1: s/buckets are configurable/buckets is configurable/ s3.1, para 3: s/This number is is/This number is/ s3.1, para 3: OLD: until the number of credits runs into the negative NEW: until the value of _byte credit_ becomes negative END What about _byte_credit_ == 0?  (Just asking!  Did possibly think that if the queue has the same number of bytes as the credit, it might be possible for the queue to jam in the active list while empty.) s3.1,para 4: s/fairness queueing/fairness queueing scheme/ s3.1, last para: s/flow-building queues/queues that build a backlog/ s4.1, para 2: A reference for Jenkins hash functions would be desirable.  It seems the best we can probably do is Jenkins' web site: http://www.burtleburtle.net/bob/hash/doobs.html s4.1:  The basic Jenkins has used in the Linux scheduler code appears to be targeted at IPv4 32 bit addresses.  Technically, the abstract definition doesn't need to worry about the lengths of addresses, but does anything special need to be said about IPv6?  I couldn't see in the Linux code where IPv6 is dealt with.  Furthermore, looking at the code a bit more closely, I am not sure how the 112 bits (32 + 32 + 16 + 16 + 16) of the 5-tuple are pushed into the hashing algorithm which has an input 'bandwidth' of 64 bits.  Again this doesn't desperately matter here but, if I understand correctly, the calculations in s5.3 of hash collision probabilities reported in para 2 of s5.3 relate to the Jenkins update3 has algorithm used in Linux.  This isn't explicitly stated.  I am not sure if the probabilities would be different if the number of bits in the 5-tuple was greater - presumably this depends to some extent on how the Jenkins algorithms are used.  The core Linux algorithm just uses the 'final' part of the algorithm.  According to the Jenkins comments, one probably ought to use the 'mix' part to combine additional bits.  Thoughts? s4.1, para 2:  I am not sure that 'permuted by a random value' is very clear, and it doesn't explain why this is done. How about 'salted by modular addition of a random value'?  It would also be helpful to note here that this is done to mitigate a possible DoS attack that could occur if the hash is externally predictable and point to the note about this in the Security Considerations (s8). s4.1.1, para 1: s/mac address/MAC address/; s/diffserv/diffserve codepoint values/ [I am not sure what firewall specific markings might be - any references?] s4.1.1, para 2:  Suggest: OLD: An alternative to changing the classification scheme is to perform    decapsulation prior to hashing. NEW: An addition to the default classification scheme is to perform    decapsulation of tunnelled packets prior to hashing on the 5-tuple in the encapsulated. END Figure in s4.2: Needs a caption and a Figure number.  It is also somewhat incomplete as a state diagram.  Both New and Old states have actions that result from both Arrival/Enqueue and Dequeue events, and there are 'loopback' actions when there are  Arrival/Enqueue and Dequeue events that occur in both New and Old states when the conditions are not satisfied. s5.2.1, para 1: to ensure that the measured minimum delay does not become too stale. Without detailed knowledge of CoDel this didn't read very easily - it is taken out of context from the CoDel draft. Suggest:    to  ensure that the minimum sojourn time of packets in a queue used as an estimator by the CoDel control algorithm is a relatively up-to-date value. s5.2.1, para 1: s/It SHOULD be set on the order/It SHOULD be set to be on the order/ s5.2.3, para 2: s/10GigE/10 Gigabit Ethernet/ s5.2.4, para 2: Expand TSO (TCP Segmentation Offload). TSO probably could do with a reference (Freimuth below should work). s5.2.4, para 2: I think GRO-enabled should probably be GSO-enabled - whichever it is, it needs to be expanded (Generic Segmentation Offload?).   There is also a web page for GSO ( https://lwn.net/Articles/188489/ )  s5.2.5, para 2 and s4.1, para 2: It would be sensible to use a common term for 'initialisation time' and 'load time'. s5.2.6, title and body: Need to expand ECN on first use.  Also s/thus unresponsive/thus the number of unresponsive/ s5.2.7: Expand CE (Congestion Encountered) on first occurrence. s5.2.7, para 1: Expand DCTCP acronym and provide reference [Alizadeh] below and/or [draft-ietf-tcpm-dctcp]....thus.. OLD: This parameter enables DCTCP-like processing to enable CE marking ECT packets at a lower setpoint than the default codel target. NEW: This parameter enables Date Centre TCP (DCTCP)-like processing resulting in CE (Congestion Encountered) marking on ECN-Capable Transport (ECT) packets [RFC3168] starting at a lower sojourn delay setpoint than the default CoDel Target. Details of DCTCP can be found in [Alizadeh2011] and [I-D.draft-ietf-tcpm-dctcp]. END s5.3, para 2: see the comments on s4.1 above regarding the link between probabilities and address lengths. s5.3, para 3: Need to expand Cake acronym and providepointer to Section 7 which expalisn about Cake. s5.4: Is it possible to add some comments to the codel_vars structure? s5.5, para 2: s/resolution below the target/resolution significantly finer than the CoDel Target setting/ s5.6: Need to expand SFQ, WFQ and QFQ.  There is a reference for SFQ below [McKenney] s5.7, last para: s/doesn't miss a beat/reacts almost immediately/ (Original is rather too colloquial!) s6.1, last para: s/classification/service classification/ s7: I might add 'Checking behaviour when two or more instantiations of FQ-CoDel are used in series.' s12.2:  Various of the informative references could do with completion.  I think the referecnes below are correct: Kathleen Nichols and Van Jacobson. 2012. "Controlling Queue Delay". Queue 10, 5 (May 2012), 20. DOI: http://dx.doi.org/10.1145/2208917.2209336 M. Shreedhar and George Varghese. 1996. "Efficient fair queuing using deficit round-robin". IEEE/ACM Trans. Netw. 4, 3 (June 1996), 375–385. DOI: http://dx.doi.org/10.1109/90.502236 M.H. MacGregor and W. Shi. 2000. "Deficits for bursty latency-critical flows: DRR++". In Proceedings IEEE International Conference on Networks 2000 (ICON 2000). Networking Trends and Challenges in the New Millennium. IEEE Comput. Soc, 287–293. DOI: http://dx.doi.org/10.1109/ICON.2000.875803 Y. Gong, D. Rossi, C. Testa, S. Valenti, and M.D. Taht. 2013. "Fighting the bufferbloat: On the coexistence of AQM and low priority congestion control". In 2013 IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS) . IEEE, 411–416. DOI: http://dx.doi.org/10.1109/INFCOMW.2013.6562885 Giovanna Carofiglio and Luca Muscariello. 2012. "On the Impact of TCP and Per-Flow Scheduling on Internet Performance". IEEE/ACM Trans. Netw. 20, 2 (April 2012), 620–633. DOI: http://dx.doi.org/10.1109/TNET.2011.2164553 The following are extra references that I suggested above: P.E. McKenney. 1990. Stochastic fairness queueing. In Proceedings. IEEE INFOCOM ’90: Ninth Annual Joint Conference of the IEEE Computer and Communications Societies@m_The Multiple Facets of Integration . IEEE Comput. Soc. Press, 733–740. DOI: http://dx.doi.org/10.1109/INFCOM.1990.91316 Doug Freimuth et al. 2005. Server network scalability and TCP offload. In USENIX Annual Technical Conference . USENIX Association, 209–222. Mohammad Alizadeh et al. 2011. Data center TCP (DCTCP). ACM SIGCOMM Comput. Commun. Rev. 41, 4 (October 2011), 63–74. DOI: http://dx.doi.org/10.1145/2043164.1851192