Re: Comcast Network Peer Survey on DSCP/ECN for L4S
This seems to be missing some of the reasons/why things are remarked, perhaps it would be wise to bring some of the people interested in this to the various vendor-specific lists or such? For example, for some hardware types, enabling any sort of rate shaping at all will rewrite the DSCP values, even for packets that do not traverse the shaped interfaces. - Jared > On Jun 10, 2022, at 9:31 AM, Livingood, Jason via NANOG > wrote: > > Hi – Comcast is working on the implementation of ultra-low latency > networking, leveraging the IETF’s upcoming L4S standard. This standard will > require passing ECN and DSCP markings across network boundaries. As a result, > we are interested in your perspective on this and in how you handle markings > today. We have a short survey that should only take a few minutes to > complete. Take the survey at https://forms.office.com/r/vGb0LUXfS1 > > While any network operator is welcome to take this, we are particularly > interested in any networks that are directly interconnected with us today. > > Thank you! > Jason Livingood > Comcast – Technology Policy & Standards > jason_living...@comcast.com > > PS – Apologies if any of you get a duplicate of this request via other > channels.
Re: Comcast Network Peer Survey on DSCP/ECN for L4S
I would argue that question 9 needs an option of "Both". Secondly, two additional good questions to ask would be: are the ECN values presently being treated as RFC3168? Are the ECN values being modified by any AQM implementations (WRED, FQ_CODEL, etc) on any switch or router in transit?
Comcast Network Peer Survey on DSCP/ECN for L4S
Hi – Comcast is working on the implementation of ultra-low latency networking, leveraging the IETF’s upcoming L4S standard. This standard will require passing ECN and DSCP markings across network boundaries. As a result, we are interested in your perspective on this and in how you handle markings today. We have a short survey that should only take a few minutes to complete. Take the survey at https://forms.office.com/r/vGb0LUXfS1 While any network operator is welcome to take this, we are particularly interested in any networks that are directly interconnected with us today. Thank you! Jason Livingood Comcast – Technology Policy & Standards jason_living...@comcast.com PS – Apologies if any of you get a duplicate of this request via other channels.
Re: TCP and anycast (was Re: ECN)
--- ra...@psg.com wrote: lots of good research lit on catchment topology of anycasted dns, which is very non-local. --- For the others here that didn't know what that is and are curious. I couldn't take it and just had to know... :) https://tools.ietf.org/html/rfc4786 Catchment: in physical geography, an area drained by a river, also known as a drainage basin. By analogy, as used in this document, the topological region of a network within which packets directed at an Anycast Address are routed to one particular node. scott
Re: TCP and anycast (was Re: ECN)
On Thu, Nov 14, 2019 at 1:10 AM Bill Woodcock wrote: > > On Nov 14, 2019, at 7:39 AM, Anoop Ghanwani wrote: > > RFC 7094 (https://tools.ietf.org/html/rfc7094) describes the pitfalls & risks of using TCP with an anycast address. It recognizes that there are valid use cases for it, though. > > Specifically, section 3.1 says this: > >Most stateful transport protocols (e.g., TCP), without modification, do not understand the properties of anycast; hence, they will fail > >probabilistically, but possibly catastrophically, when using anycast addresses in the presence of "normal" routing dynamics. > >This can lead to a protocol working fine in, say, a test lab but not in the global Internet. > > > > On Thu, Nov 14, 2019 at 12:25 AM Matt Corallo wrote: > > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP is... out of spec to say the least), > > No. We have been doing anycast TCP for more than _thirty years_, most of that time on a global scale, without operational problems. Hi Bill, Not to put to fine a point on it but Baldur and Toke's scenario in which anycast tcp failed, the one which started this thread, should probably be classed as an operational problem. It is possible to build an anycast TCP that works. YOU have not done so. And Cloudflare certainly has not. Regards, Bill Herrin -- William Herrin b...@herrin.us https://bill.herrin.us/
Re: TCP and anycast (was Re: ECN)
>>> RFC 7094 (https://tools.ietf.org/html/rfc7094) describes the pitfalls >>> & risks of using TCP with an anycast address. >> >> and two decades of operational experience are that prudent deployments >> just work. > > I agree with Bill/Randy here... this does just work if you understand > your local topology and manage change properly. agree, but would extend ... sometimes s/local// i.e. casting from your edge dumps directly to peers, keeping it off your backbone. but the topo set you have to keep in mind can be large. lots of good research lit on catchment topology of anycasted dns, which is very non-local. randy
Re: TCP and anycast (was Re: ECN)
On Fri, Nov 15, 2019 at 1:54 AM Randy Bush wrote: > > > RFC 7094 (https://tools.ietf.org/html/rfc7094) describes the pitfalls > > & risks of using TCP with an anycast address. > > and two decades of operational experience are that prudent deployments > just work. I agree with Bill/Randy here... this does just work if you understand your local topology and manage change properly.
Re: TCP and anycast (was Re: ECN)
> RFC 7094 (https://tools.ietf.org/html/rfc7094) describes the pitfalls > & risks of using TCP with an anycast address. and two decades of operational experience are that prudent deployments just work. randy
Re: ECN
Owen DeLong writes: > Like it or not (and I really don’t), the majority of modern CDNs are > using TCP over Anycast. > > It’s ugly and it’s prone to problems like this. It’s nice to see a > customer with know-how actually publicizing and digging into the > problem. Thanks. I do plan to write this whole story up as a blog post, BTW. Apart from just being a nice "battle story" I also think it's important to get more visibility into these kinds of issues. I've mostly been interested in issues related to ECN in general, but its interaction with anycast is certainly... interesting :) > Until now, I believe an unknown number of customers have been > suffering in silence or relegated to the ISPs “We can’t reproduce you > problem” bin without resolution. > > I’ve had lots of discussions on the subject and the usual end result > is “It’s too hard to measure or quantify and there’s no visible > contingent of impacted users”. > > Now we at least have one visible impacted user. As I said, happy to be an exponent if it can help others resolve these kinds of problems. Incidentally, in case you're not aware, there are currently two competing schemes being discussed at the IETF to re-purpose the ECT(1) code point in the IP header. One proposal[0] is to use it as an additional high-fidelity congestion indicator, while the other[1] is to use it as an identifier for a new type of traffic that should get special treatment (which almost, but not quite, amounts to priority queueing). So if either proposal gains traction, expect more ECN-marked traffic coming to a network near you in the maybe-not-so-distant future; with all the interesting issues that can bring with it. If someone feels like introducing some operational considerations into the IETF discussions, I do believe both drafts will be discussed at the tsvwg working group meetings at the Singapore IETF next week. -Toke [0] https://datatracker.ietf.org/doc/draft-morton-tsvwg-sce/ [1] https://datatracker.ietf.org/doc/draft-ietf-tsvwg-ecn-l4s-id/
Re: ECN
Baldur Norddahl writes: > I am testing disabling our use of ECMP as it is not strictly necessary > and we are moving to a new platform anyway. Waiting for feedback from > the customer to hear if this fixes the issue. Which I can confirm that it does. Thank you for the speedy resolution! :) -Toke
Re: ECN
On Wed, 13 Nov 2019 at 22:57, Lukas Tribus wrote: > In fact I believe everything beyond the 5-tuple is just a bad idea to > base your hash on. Here are some examples (not quite as straight > forward than the TOS/ECN case here): ACK. > TTL: > https://mailman.nanog.org/pipermail/nanog/2018-September/096871.html > IPv6 flow label: > https://blog.apnic.net/2018/01/11/ipv6-flow-label-misuse-hashing/ > https://pc.nanog.org/static/published/meetings/NANOG71/1531/20171003_Jaeggli_Lightning_Talk_Ipv6_v1.pdf > https://www.youtube.com/watch?v=b0CRjOpnT7w It is unfortunate IPv6 flow label is so poorly specified, had it been specified clearly it could have been very very good for the Internet. Crucially sender should be able to instruct transit HOW to hash, there should be flags in flow label used by sender to indicate that flow label must be used for hash exclusively, not at all, inclusively with what ever host otherwise uses. This would give sender control over what is discreet flow. Something like this https://ytti.github.io/flow-label/draft-ytti-v6ops-flow-label.html would have been nice, but unclear if it would be possible to deliver post-fact -- ++ytti
Re: TCP and anycast (was Re: ECN)
> On Nov 14, 2019, at 7:39 AM, Anoop Ghanwani wrote: > RFC 7094 (https://tools.ietf.org/html/rfc7094) describes the pitfalls & risks > of using TCP with an anycast address. It recognizes that there are valid use > cases for it, though. > Specifically, section 3.1 says this: >Most stateful transport protocols (e.g., TCP), without modification, do > not understand the properties of anycast; hence, they will fail >probabilistically, but possibly catastrophically, when using anycast > addresses in the presence of "normal" routing dynamics. >This can lead to a protocol working fine in, say, a test lab but not in > the global Internet. > > On Thu, Nov 14, 2019 at 12:25 AM Matt Corallo wrote: > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP > > is... out of spec to say the least), No. We have been doing anycast TCP for more than _thirty years_, most of that time on a global scale, without operational problems. There were people who seemed gray-bearded at the time, who were scared of anycast because it used IP addresses _non uniquely_ and that wasn’t how they’d intended them to be used, and these kids these days, etc. What you’re seeing is residuum of their pronouncements on the matter, carrying over from the mid-1990s. It’s very true that anycast can be misused and abused in a myriad of ways, leading to unexpected or unpleasant results, but no more so than other routing techniques. We and others have published on many or most of the potential issues and their solutions over the years. That RFC has never actually been a comprehensive source of information on the topic, and it contains a lot of scare-mongering. -Bill
Re: ECN
* Saku Ytti > Not true. Hash result should indicate discreet flow, more importantly > discreet flow should not result into two unique hash numbers. Using > whole TOS byte breaks this promise and thus breaks ECMP. > > Platforms allow you to configure which bytes are part of hash > calculation, whole TOS byte should not be used as discreet flow SHOULD > have unique ECN bits during congestion. Toke has diagnosed the problem > correctly, solution is to remove TOS from ECMP hash calculation. Agreed. This also goes for the other bits, so whole byte must be excluded. For example, the OpenSSH client will by default change the code point from zero (during authentication) to af21/cs1 (when it enters a interactive/non-interactive session). I have experienced this break IPv6 SSH sessions to an anycasted SSH server instance that was reached through old Juniper DPC cards with ECMP enabled. Symptom was that authentication went fine, only for the connection to be reset immediately after (unless default IPQoS config was changed). The «solution» was to simply disable ECMP for all IPv6 traffic, since I could not figure out how to make the Juniper exclude the DiffServ byte from the ECMP hash calculation. Tore
TCP and anycast (was Re: ECN)
RFC 7094 (https://tools.ietf.org/html/rfc7094) describes the pitfalls & risks of using TCP with an anycast address. It recognizes that there are valid use cases for it, though. Specifically, section 3.1 says this: >>> Most stateful transport protocols (e.g., TCP), without modification, do not understand the properties of anycast; hence, they will fail probabilistically, but possibly catastrophically, when using anycast addresses in the presence of "normal" routing dynamics. ... This can lead to a protocol working fine in, say, a test lab but not in the global Internet. >>> On Wed, Nov 13, 2019 at 3:33 PM Warren Kumari wrote: > On Thu, Nov 14, 2019 at 12:25 AM Matt Corallo wrote: > > > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast > TCP is... out of spec to say the least), not a bug in ECN/ECMP. > > Err. I really don't think that there is any sort of spec that > covers that :-P > > Using Anycast for TCP is incredibly common - the DNS root servers for > one obvious example. > More TCP centric well-known examples are Fastly and LinkedIn - > LinkedIn in particular did a really good podcast on their experience > with this. > > There is also a good NANOG talk from the ~2000s (?) on people using > TCP anycast for long lived (serving ISO files, which were long-lived > in those days) flows, and how reliable it is - perhaps that's the talk > Todd mentioned? > > W > > > > > > On Nov 13, 2019, at 11:07, Toke Høiland-Jørgensen via NANOG < > nanog@nanog.org> wrote: > > > > > > > > >> > > >> Hello > > >> > > >> I have a customer that believes my network has a ECN problem. We do > > >> not, we just move packets. But how do I prove it? > > >> > > >> Is there a tool that checks for ECN trouble? Ideally something I could > > >> run on the NLNOG Ring network. > > >> > > >> I believe it likely that it is the destination that has the problem. > > > > > > Hi Baldur > > > > > > I believe I may be that customer :) > > > > > > First of all, thank you for looking into the issue! We've been having > > > great fun over on the ecn-sane mailing list trying to figure out what's > > > going on. I'll summarise below, but see this thread for the discussion > > > and debugging details: > > > > https://lists.bufferbloat.net/pipermail/ecn-sane/2019-November/000527.html > > > > > > The short version is that the problem appears to come from a > combination > > > of the ECMP routing in your network, and Cloudflare's heavy use of > > > anycast. Specifically, a router in your network appears to be doing > ECMP > > > by hashing on the packet header, *including the ECN bits*. This breaks > > > TCP connections with ECN because the TCP SYN (with no ECN bits set) end > > > up taking a different path than the rest of the flow (which is marked > as > > > ECT(0)). When the destination is anycasted, this means that the data > > > packets go to a different server than the SYN did. This second server > > > doesn't recognise the connection, and so replies with a TCP RST. To fix > > > this, simply exclude the ECN bits (or the whole TOS byte) from your > > > router's ECMP hash. > > > > > > For a longer exposition, see below. You should be able to verify this > > > from somewhere else in the network, but if there's anything else you > > > want me to test, do let me know. Also, would you mind sharing the > router > > > make and model that does this? We're trying to collect real-world > > > examples of network problems caused by ECN and this is definitely an > > > interesting example. > > > > > > -Toke > > > > > > > > > > > > The long version: > > > > > > From my end I can see that I have two paths to Cloudflare; which is > > > taken appears to be based on a hash of the packet header, as can be > seen > > > by varying the source port: > > > > > > $ traceroute -q 1 --sport=1 104.24.125.13 > > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte > packets > > > 1 _gateway (10.42.3.1) 0.357 ms > > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 4.707 ms > > > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.283 ms > > > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.667 ms > > > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.406 ms >
Re: ECN
On Thu, Nov 14, 2019 at 12:25 AM Matt Corallo wrote: > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP > is... out of spec to say the least), not a bug in ECN/ECMP. Err. I really don't think that there is any sort of spec that covers that :-P Using Anycast for TCP is incredibly common - the DNS root servers for one obvious example. More TCP centric well-known examples are Fastly and LinkedIn - LinkedIn in particular did a really good podcast on their experience with this. There is also a good NANOG talk from the ~2000s (?) on people using TCP anycast for long lived (serving ISO files, which were long-lived in those days) flows, and how reliable it is - perhaps that's the talk Todd mentioned? W > > > On Nov 13, 2019, at 11:07, Toke Høiland-Jørgensen via NANOG > > wrote: > > > > > >> > >> Hello > >> > >> I have a customer that believes my network has a ECN problem. We do > >> not, we just move packets. But how do I prove it? > >> > >> Is there a tool that checks for ECN trouble? Ideally something I could > >> run on the NLNOG Ring network. > >> > >> I believe it likely that it is the destination that has the problem. > > > > Hi Baldur > > > > I believe I may be that customer :) > > > > First of all, thank you for looking into the issue! We've been having > > great fun over on the ecn-sane mailing list trying to figure out what's > > going on. I'll summarise below, but see this thread for the discussion > > and debugging details: > > https://lists.bufferbloat.net/pipermail/ecn-sane/2019-November/000527.html > > > > The short version is that the problem appears to come from a combination > > of the ECMP routing in your network, and Cloudflare's heavy use of > > anycast. Specifically, a router in your network appears to be doing ECMP > > by hashing on the packet header, *including the ECN bits*. This breaks > > TCP connections with ECN because the TCP SYN (with no ECN bits set) end > > up taking a different path than the rest of the flow (which is marked as > > ECT(0)). When the destination is anycasted, this means that the data > > packets go to a different server than the SYN did. This second server > > doesn't recognise the connection, and so replies with a TCP RST. To fix > > this, simply exclude the ECN bits (or the whole TOS byte) from your > > router's ECMP hash. > > > > For a longer exposition, see below. You should be able to verify this > > from somewhere else in the network, but if there's anything else you > > want me to test, do let me know. Also, would you mind sharing the router > > make and model that does this? We're trying to collect real-world > > examples of network problems caused by ECN and this is definitely an > > interesting example. > > > > -Toke > > > > > > > > The long version: > > > > From my end I can see that I have two paths to Cloudflare; which is > > taken appears to be based on a hash of the packet header, as can be seen > > by varying the source port: > > > > $ traceroute -q 1 --sport=1 104.24.125.13 > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > > 1 _gateway (10.42.3.1) 0.357 ms > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 4.707 ms > > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.283 ms > > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.667 ms > > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.406 ms > > 6 104.24.125.13 (104.24.125.13) 1.322 ms > > > > $ traceroute -q 1 --sport=10001 104.24.125.13 > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > > 1 _gateway (10.42.3.1) 0.293 ms > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 3.430 ms > > 3 customer-185-24-168-38.ip4.gigabit.dk (185.24.168.38) 1.194 ms > > 4 10ge1-2.core1.cph1.he.net (216.66.83.101) 1.297 ms > > 5 be2306.ccr42.ham01.atlas.cogentco.com (130.117.3.237) 6.805 ms > > 6 149.6.142.130 (149.6.142.130) 6.925 ms > > 7 104.24.125.13 (104.24.125.13) 1.501 ms > > > > > > This is fine in itself. However, the problem stems from the fact that > > the ECN bits in the IP header are also included in the ECMP hash (-t > > sets the TOS byte; -t 1 ends up as ECT(0) on the wire and -t 2 is > > ECT(1)): > > > > $ traceroute -q 1 --sport=1 104.24.125.13 -t 1 > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > > 1 _gateway (10.42.3.1) 0.336 ms > > 2 alber
Re: ECN
Hello, On Wed, Nov 13, 2019 at 8:35 PM Saku Ytti wrote: > > On Wed, 13 Nov 2019 at 18:27, Matt Corallo wrote: > > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP > > is... out of spec to say the least), not a bug in ECN/ECMP. > > Not true. Hash result should indicate discreet flow, more importantly > discreet flow should not result into two unique hash numbers. Using > whole TOS byte breaks this promise and thus breaks ECMP. > > Platforms allow you to configure which bytes are part of hash > calculation, whole TOS byte should not be used as discreet flow SHOULD > have unique ECN bits during congestion. Toke has diagnosed the problem > correctly, solution is to remove TOS from ECMP hash calculation. In fact I believe everything beyond the 5-tuple is just a bad idea to base your hash on. Here are some examples (not quite as straight forward than the TOS/ECN case here): TTL: https://mailman.nanog.org/pipermail/nanog/2018-September/096871.html IPv6 flow label: https://blog.apnic.net/2018/01/11/ipv6-flow-label-misuse-hashing/ https://pc.nanog.org/static/published/meetings/NANOG71/1531/20171003_Jaeggli_Lightning_Talk_Ipv6_v1.pdf https://www.youtube.com/watch?v=b0CRjOpnT7w Lukas
Re: ECN
On Wed, Nov 13, 2019 at 11:36 AM Saku Ytti wrote: > On Wed, 13 Nov 2019 at 18:27, Matt Corallo wrote: > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast > TCP is... out of spec to say the least), not a bug in ECN/ECMP. > > Not true. Hash result should indicate discreet flow, more importantly > discreet flow should not result into two unique hash numbers. Using > whole TOS byte breaks this promise and thus breaks ECMP. > Yes true. Equal Cost MultiPath (ECMP) consistency over the life of a TCP connection is not a promise. Anycasters would love it to be but it's not. ECMP's only promise is that packets for a particular connection will tend to prefer a particular path so that throughput doesn't suffer overly much from the packet reordering you'd get by round-robining the packets on different links. Choosing an alternate path during congestion is a perfectly reasonable thing for ECMP to do. Don't blame the network. This is Cloudflare choosing not to handle the anycast spray corner case because it happens rarely enough with symptoms obscure enough that they only occasionally get called to carpet. Their BGP announcements make the claim they're ready for your packet at any of their sites, but they're not. Regards, Bill Herrin -- William Herrin b...@herrin.us https://bill.herrin.us/
Re: ECN
Like it or not (and I really don’t), the majority of modern CDNs are using TCP over Anycast. It’s ugly and it’s prone to problems like this. It’s nice to see a customer with know-how actually publicizing and digging into the problem. Until now, I believe an unknown number of customers have been suffering in silence or relegated to the ISPs “We can’t reproduce you problem” bin without resolution. I’ve had lots of discussions on the subject and the usual end result is “It’s too hard to measure or quantify and there’s no visible contingent of impacted users”. Now we at least have one visible impacted user. Owen > On Nov 13, 2019, at 09:19 , Anoop Ghanwani wrote: > > Not to condone what cloudflare is doing, but... > > An ECN connection will have different bits on various packets for the > duration of the connection -- pure ACKs (ACKs not piggybacking on data) will > have the ECN bits as 00b, while all other packets will have either 01b, 10b > (when no congestion was experienced) or 11b (when congestion was > experienced). So using the ECN bits as part of the hash would affect > performance throughout the life of the connection. > > On Wed, Nov 13, 2019 at 9:00 AM Matt Corallo <mailto:na...@as397444.net>> wrote: > Not ideal, sure, but if it’s only for the SYN (as you seem to indicate), > splitting the flow shouldn’t have material performance degradation? > > > On Nov 13, 2019, at 11:51, Toke Høiland-Jørgensen > <mailto:t...@toke.dk>> wrote: > > > > > > > >> On 13 November 2019 17:20:18 CET, Matt Corallo >> <mailto:netad...@as397444.net>> wrote: > >> This sounds like a bug on Cloudflare’s end (cause trying to do anycast > >> TCP is... out of spec to say the least), not a bug in ECN/ECMP. > > > > Even without anycast, an ECMP shouldn't hash on the ECN bits. Doing so will > > split the flow over multiple paths; avoiding that is the whole point of > > doing the flow-based hashing in the first place. > > > > Anycast "only" turns a potential degradation of TCP performance into a hard > > failure... :) > > > > -Toke >
Re: ECN
On Wed, 13 Nov 2019 at 18:27, Matt Corallo wrote: > This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP > is... out of spec to say the least), not a bug in ECN/ECMP. Not true. Hash result should indicate discreet flow, more importantly discreet flow should not result into two unique hash numbers. Using whole TOS byte breaks this promise and thus breaks ECMP. Platforms allow you to configure which bytes are part of hash calculation, whole TOS byte should not be used as discreet flow SHOULD have unique ECN bits during congestion. Toke has diagnosed the problem correctly, solution is to remove TOS from ECMP hash calculation. -- ++ytti
Re: ECN
On 13 November 2019 17:20:18 CET, Matt Corallo wrote: >This sounds like a bug on Cloudflare’s end (cause trying to do anycast >TCP is... out of spec to say the least), not a bug in ECN/ECMP. Even without anycast, an ECMP shouldn't hash on the ECN bits. Doing so will split the flow over multiple paths; avoiding that is the whole point of doing the flow-based hashing in the first place. Anycast "only" turns a potential degradation of TCP performance into a hard failure... :) -Toke
Re: ECN
ZTE M6000-S V3.00.20(3.40.1) We are moving away from this platform so I can not be bothered with requesting a fix. In the past they have made fixes for us, so I believe they would also fix this issue if we asked them to do so. Also I would like to state that I have not personally verified that the equipment is doing hashing based on the ECN bits. I just turned off ECMP so the customer can test. If it works we will either let ECMP stay off or move the customer to the new platform. Regards, Baldur On Wed, Nov 13, 2019 at 7:30 PM Mikael Abrahamsson wrote: > On Wed, 13 Nov 2019, Baldur Norddahl wrote: > > > In any case, is it not recommended that users of anycast proxy packets > > that arrive at the wrong place? To avoid this kind of issue. > > In typical anycast deployments there is no feasible way to figure out > where the "right place" is. > > It would be very interesting if your could share what equipment you're > using that is doing ECMP hashing based on ECN bits. That vendor needs to > fix that or people should avoid their devices. > > -- > Mikael Abrahamssonemail: swm...@swm.pp.se >
Re: ECN
On Wed, 13 Nov 2019, Baldur Norddahl wrote: In any case, is it not recommended that users of anycast proxy packets that arrive at the wrong place? To avoid this kind of issue. In typical anycast deployments there is no feasible way to figure out where the "right place" is. It would be very interesting if your could share what equipment you're using that is doing ECMP hashing based on ECN bits. That vendor needs to fix that or people should avoid their devices. -- Mikael Abrahamssonemail: swm...@swm.pp.se
Re: ECN
I am testing disabling our use of ECMP as it is not strictly necessary and we are moving to a new platform anyway. Waiting for feedback from the customer to hear if this fixes the issue. In any case, is it not recommended that users of anycast proxy packets that arrive at the wrong place? To avoid this kind of issue. Regards, Baldur On Wed, Nov 13, 2019 at 6:35 PM Todd Underwood wrote: > as one of the authors of that talk, it definitely is "a thing", has been > for years and years and years, and indeed, mostly works. > > t > > On Wed, Nov 13, 2019 at 12:18 PM Hunter Fuller > wrote: > >> It is certainly odd, but it's definitely a "thing." >> >> https://archive.nanog.org/meetings/nanog37/presentations/matt.levine.pdf >> >> On Wed, Nov 13, 2019 at 10:24 AM Matt Corallo wrote: >> > >> > This sounds like a bug on Cloudflare’s end (cause trying to do anycast >> TCP is... out of spec to say the least), not a bug in ECN/ECMP. >> > >> > > On Nov 13, 2019, at 11:07, Toke Høiland-Jørgensen via NANOG < >> nanog@nanog.org> wrote: >> > > >> > > >> > >> >> > >> Hello >> > >> >> > >> I have a customer that believes my network has a ECN problem. We do >> > >> not, we just move packets. But how do I prove it? >> > >> >> > >> Is there a tool that checks for ECN trouble? Ideally something I >> could >> > >> run on the NLNOG Ring network. >> > >> >> > >> I believe it likely that it is the destination that has the problem. >> > > >> > > Hi Baldur >> > > >> > > I believe I may be that customer :) >> > > >> > > First of all, thank you for looking into the issue! We've been having >> > > great fun over on the ecn-sane mailing list trying to figure out >> what's >> > > going on. I'll summarise below, but see this thread for the discussion >> > > and debugging details: >> > > >> https://lists.bufferbloat.net/pipermail/ecn-sane/2019-November/000527.html >> > > >> > > The short version is that the problem appears to come from a >> combination >> > > of the ECMP routing in your network, and Cloudflare's heavy use of >> > > anycast. Specifically, a router in your network appears to be doing >> ECMP >> > > by hashing on the packet header, *including the ECN bits*. This breaks >> > > TCP connections with ECN because the TCP SYN (with no ECN bits set) >> end >> > > up taking a different path than the rest of the flow (which is marked >> as >> > > ECT(0)). When the destination is anycasted, this means that the data >> > > packets go to a different server than the SYN did. This second server >> > > doesn't recognise the connection, and so replies with a TCP RST. To >> fix >> > > this, simply exclude the ECN bits (or the whole TOS byte) from your >> > > router's ECMP hash. >> > > >> > > For a longer exposition, see below. You should be able to verify this >> > > from somewhere else in the network, but if there's anything else you >> > > want me to test, do let me know. Also, would you mind sharing the >> router >> > > make and model that does this? We're trying to collect real-world >> > > examples of network problems caused by ECN and this is definitely an >> > > interesting example. >> > > >> > > -Toke >> > > >> > > >> > > >> > > The long version: >> > > >> > > From my end I can see that I have two paths to Cloudflare; which is >> > > taken appears to be based on a hash of the packet header, as can be >> seen >> > > by varying the source port: >> > > >> > > $ traceroute -q 1 --sport=1 104.24.125.13 >> > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte >> packets >> > > 1 _gateway (10.42.3.1) 0.357 ms >> > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 4.707 ms >> > > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.283 ms >> > > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.667 ms >> > > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.406 ms >> > > 6 104.24.125.13 (104.24.125.13) 1.322 ms >> > > >> > > $ traceroute -q 1 --sport=10001 104.24.125.13 >> > > traceroute to 104.24.125.
Re: ECN
It does when the split flows land in different anycast origin POPs. Making a few assumptions from the traceroutes, the ECMP paths are sending some packets to Hamburg and some to Denmark. Each POP may be getting parts of what should be a single TCP stream, and I doubt they have anything to cope with that (another assumption). On Wed, 13 Nov 2019, Matt Corallo wrote: Not ideal, sure, but if it’s only for the SYN (as you seem to indicate), splitting the flow shouldn’t have material performance degradation? On Nov 13, 2019, at 11:51, Toke Høiland-Jørgensen wrote: On 13 November 2019 17:20:18 CET, Matt Corallo wrote: This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP is... out of spec to say the least), not a bug in ECN/ECMP. Even without anycast, an ECMP shouldn't hash on the ECN bits. Doing so will split the flow over multiple paths; avoiding that is the whole point of doing the flow-based hashing in the first place. Anycast "only" turns a potential degradation of TCP performance into a hard failure... :) -Toke -- Jon Lewis, MCP :) | I route StackPath, Sr. Neteng | therefore you are _ http://www.lewis.org/~jlewis/pgp for PGP public key_
Re: ECN
as one of the authors of that talk, it definitely is "a thing", has been for years and years and years, and indeed, mostly works. t On Wed, Nov 13, 2019 at 12:18 PM Hunter Fuller wrote: > It is certainly odd, but it's definitely a "thing." > > https://archive.nanog.org/meetings/nanog37/presentations/matt.levine.pdf > > On Wed, Nov 13, 2019 at 10:24 AM Matt Corallo wrote: > > > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast > TCP is... out of spec to say the least), not a bug in ECN/ECMP. > > > > > On Nov 13, 2019, at 11:07, Toke Høiland-Jørgensen via NANOG < > nanog@nanog.org> wrote: > > > > > > > > >> > > >> Hello > > >> > > >> I have a customer that believes my network has a ECN problem. We do > > >> not, we just move packets. But how do I prove it? > > >> > > >> Is there a tool that checks for ECN trouble? Ideally something I could > > >> run on the NLNOG Ring network. > > >> > > >> I believe it likely that it is the destination that has the problem. > > > > > > Hi Baldur > > > > > > I believe I may be that customer :) > > > > > > First of all, thank you for looking into the issue! We've been having > > > great fun over on the ecn-sane mailing list trying to figure out what's > > > going on. I'll summarise below, but see this thread for the discussion > > > and debugging details: > > > > https://lists.bufferbloat.net/pipermail/ecn-sane/2019-November/000527.html > > > > > > The short version is that the problem appears to come from a > combination > > > of the ECMP routing in your network, and Cloudflare's heavy use of > > > anycast. Specifically, a router in your network appears to be doing > ECMP > > > by hashing on the packet header, *including the ECN bits*. This breaks > > > TCP connections with ECN because the TCP SYN (with no ECN bits set) end > > > up taking a different path than the rest of the flow (which is marked > as > > > ECT(0)). When the destination is anycasted, this means that the data > > > packets go to a different server than the SYN did. This second server > > > doesn't recognise the connection, and so replies with a TCP RST. To fix > > > this, simply exclude the ECN bits (or the whole TOS byte) from your > > > router's ECMP hash. > > > > > > For a longer exposition, see below. You should be able to verify this > > > from somewhere else in the network, but if there's anything else you > > > want me to test, do let me know. Also, would you mind sharing the > router > > > make and model that does this? We're trying to collect real-world > > > examples of network problems caused by ECN and this is definitely an > > > interesting example. > > > > > > -Toke > > > > > > > > > > > > The long version: > > > > > > From my end I can see that I have two paths to Cloudflare; which is > > > taken appears to be based on a hash of the packet header, as can be > seen > > > by varying the source port: > > > > > > $ traceroute -q 1 --sport=1 104.24.125.13 > > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte > packets > > > 1 _gateway (10.42.3.1) 0.357 ms > > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 4.707 ms > > > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.283 ms > > > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.667 ms > > > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.406 ms > > > 6 104.24.125.13 (104.24.125.13) 1.322 ms > > > > > > $ traceroute -q 1 --sport=10001 104.24.125.13 > > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte > packets > > > 1 _gateway (10.42.3.1) 0.293 ms > > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 3.430 ms > > > 3 customer-185-24-168-38.ip4.gigabit.dk (185.24.168.38) 1.194 ms > > > 4 10ge1-2.core1.cph1.he.net (216.66.83.101) 1.297 ms > > > 5 be2306.ccr42.ham01.atlas.cogentco.com (130.117.3.237) 6.805 ms > > > 6 149.6.142.130 (149.6.142.130) 6.925 ms > > > 7 104.24.125.13 (104.24.125.13) 1.501 ms > > > > > > > > > This is fine in itself. However, the problem stems from the fact that > > > the ECN bits in the IP header are also included in the ECMP hash (-t > > > sets the TOS byte; -t 1 ends up as EC
Re: ECN
Not to condone what cloudflare is doing, but... An ECN connection will have different bits on various packets for the duration of the connection -- pure ACKs (ACKs not piggybacking on data) will have the ECN bits as 00b, while all other packets will have either 01b, 10b (when no congestion was experienced) or 11b (when congestion was experienced). So using the ECN bits as part of the hash would affect performance throughout the life of the connection. On Wed, Nov 13, 2019 at 9:00 AM Matt Corallo wrote: > Not ideal, sure, but if it’s only for the SYN (as you seem to indicate), > splitting the flow shouldn’t have material performance degradation? > > > On Nov 13, 2019, at 11:51, Toke Høiland-Jørgensen wrote: > > > > > > > >> On 13 November 2019 17:20:18 CET, Matt Corallo > wrote: > >> This sounds like a bug on Cloudflare’s end (cause trying to do anycast > >> TCP is... out of spec to say the least), not a bug in ECN/ECMP. > > > > Even without anycast, an ECMP shouldn't hash on the ECN bits. Doing so > will split the flow over multiple paths; avoiding that is the whole point > of doing the flow-based hashing in the first place. > > > > Anycast "only" turns a potential degradation of TCP performance into a > hard failure... :) > > > > -Toke > >
Re: ECN
It is certainly odd, but it's definitely a "thing." https://archive.nanog.org/meetings/nanog37/presentations/matt.levine.pdf On Wed, Nov 13, 2019 at 10:24 AM Matt Corallo wrote: > > This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP > is... out of spec to say the least), not a bug in ECN/ECMP. > > > On Nov 13, 2019, at 11:07, Toke Høiland-Jørgensen via NANOG > > wrote: > > > > > >> > >> Hello > >> > >> I have a customer that believes my network has a ECN problem. We do > >> not, we just move packets. But how do I prove it? > >> > >> Is there a tool that checks for ECN trouble? Ideally something I could > >> run on the NLNOG Ring network. > >> > >> I believe it likely that it is the destination that has the problem. > > > > Hi Baldur > > > > I believe I may be that customer :) > > > > First of all, thank you for looking into the issue! We've been having > > great fun over on the ecn-sane mailing list trying to figure out what's > > going on. I'll summarise below, but see this thread for the discussion > > and debugging details: > > https://lists.bufferbloat.net/pipermail/ecn-sane/2019-November/000527.html > > > > The short version is that the problem appears to come from a combination > > of the ECMP routing in your network, and Cloudflare's heavy use of > > anycast. Specifically, a router in your network appears to be doing ECMP > > by hashing on the packet header, *including the ECN bits*. This breaks > > TCP connections with ECN because the TCP SYN (with no ECN bits set) end > > up taking a different path than the rest of the flow (which is marked as > > ECT(0)). When the destination is anycasted, this means that the data > > packets go to a different server than the SYN did. This second server > > doesn't recognise the connection, and so replies with a TCP RST. To fix > > this, simply exclude the ECN bits (or the whole TOS byte) from your > > router's ECMP hash. > > > > For a longer exposition, see below. You should be able to verify this > > from somewhere else in the network, but if there's anything else you > > want me to test, do let me know. Also, would you mind sharing the router > > make and model that does this? We're trying to collect real-world > > examples of network problems caused by ECN and this is definitely an > > interesting example. > > > > -Toke > > > > > > > > The long version: > > > > From my end I can see that I have two paths to Cloudflare; which is > > taken appears to be based on a hash of the packet header, as can be seen > > by varying the source port: > > > > $ traceroute -q 1 --sport=1 104.24.125.13 > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > > 1 _gateway (10.42.3.1) 0.357 ms > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 4.707 ms > > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.283 ms > > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.667 ms > > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.406 ms > > 6 104.24.125.13 (104.24.125.13) 1.322 ms > > > > $ traceroute -q 1 --sport=10001 104.24.125.13 > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > > 1 _gateway (10.42.3.1) 0.293 ms > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 3.430 ms > > 3 customer-185-24-168-38.ip4.gigabit.dk (185.24.168.38) 1.194 ms > > 4 10ge1-2.core1.cph1.he.net (216.66.83.101) 1.297 ms > > 5 be2306.ccr42.ham01.atlas.cogentco.com (130.117.3.237) 6.805 ms > > 6 149.6.142.130 (149.6.142.130) 6.925 ms > > 7 104.24.125.13 (104.24.125.13) 1.501 ms > > > > > > This is fine in itself. However, the problem stems from the fact that > > the ECN bits in the IP header are also included in the ECMP hash (-t > > sets the TOS byte; -t 1 ends up as ECT(0) on the wire and -t 2 is > > ECT(1)): > > > > $ traceroute -q 1 --sport=1 104.24.125.13 -t 1 > > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > > 1 _gateway (10.42.3.1) 0.336 ms > > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 6.964 ms > > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.056 ms > > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.512 ms > > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.313 ms > > 6 104.24.125.13 (104.24.125.13) 1.210 ms > > > > $ traceroute -q 1 --sport=1 104.24.125.13 -t 2
Re: ECN
Not ideal, sure, but if it’s only for the SYN (as you seem to indicate), splitting the flow shouldn’t have material performance degradation? > On Nov 13, 2019, at 11:51, Toke Høiland-Jørgensen wrote: > > > >> On 13 November 2019 17:20:18 CET, Matt Corallo wrote: >> This sounds like a bug on Cloudflare’s end (cause trying to do anycast >> TCP is... out of spec to say the least), not a bug in ECN/ECMP. > > Even without anycast, an ECMP shouldn't hash on the ECN bits. Doing so will > split the flow over multiple paths; avoiding that is the whole point of doing > the flow-based hashing in the first place. > > Anycast "only" turns a potential degradation of TCP performance into a hard > failure... :) > > -Toke
Re: ECN
This sounds like a bug on Cloudflare’s end (cause trying to do anycast TCP is... out of spec to say the least), not a bug in ECN/ECMP. > On Nov 13, 2019, at 11:07, Toke Høiland-Jørgensen via NANOG > wrote: > > >> >> Hello >> >> I have a customer that believes my network has a ECN problem. We do >> not, we just move packets. But how do I prove it? >> >> Is there a tool that checks for ECN trouble? Ideally something I could >> run on the NLNOG Ring network. >> >> I believe it likely that it is the destination that has the problem. > > Hi Baldur > > I believe I may be that customer :) > > First of all, thank you for looking into the issue! We've been having > great fun over on the ecn-sane mailing list trying to figure out what's > going on. I'll summarise below, but see this thread for the discussion > and debugging details: > https://lists.bufferbloat.net/pipermail/ecn-sane/2019-November/000527.html > > The short version is that the problem appears to come from a combination > of the ECMP routing in your network, and Cloudflare's heavy use of > anycast. Specifically, a router in your network appears to be doing ECMP > by hashing on the packet header, *including the ECN bits*. This breaks > TCP connections with ECN because the TCP SYN (with no ECN bits set) end > up taking a different path than the rest of the flow (which is marked as > ECT(0)). When the destination is anycasted, this means that the data > packets go to a different server than the SYN did. This second server > doesn't recognise the connection, and so replies with a TCP RST. To fix > this, simply exclude the ECN bits (or the whole TOS byte) from your > router's ECMP hash. > > For a longer exposition, see below. You should be able to verify this > from somewhere else in the network, but if there's anything else you > want me to test, do let me know. Also, would you mind sharing the router > make and model that does this? We're trying to collect real-world > examples of network problems caused by ECN and this is definitely an > interesting example. > > -Toke > > > > The long version: > > From my end I can see that I have two paths to Cloudflare; which is > taken appears to be based on a hash of the packet header, as can be seen > by varying the source port: > > $ traceroute -q 1 --sport=1 104.24.125.13 > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > 1 _gateway (10.42.3.1) 0.357 ms > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 4.707 ms > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.283 ms > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.667 ms > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.406 ms > 6 104.24.125.13 (104.24.125.13) 1.322 ms > > $ traceroute -q 1 --sport=10001 104.24.125.13 > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > 1 _gateway (10.42.3.1) 0.293 ms > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 3.430 ms > 3 customer-185-24-168-38.ip4.gigabit.dk (185.24.168.38) 1.194 ms > 4 10ge1-2.core1.cph1.he.net (216.66.83.101) 1.297 ms > 5 be2306.ccr42.ham01.atlas.cogentco.com (130.117.3.237) 6.805 ms > 6 149.6.142.130 (149.6.142.130) 6.925 ms > 7 104.24.125.13 (104.24.125.13) 1.501 ms > > > This is fine in itself. However, the problem stems from the fact that > the ECN bits in the IP header are also included in the ECMP hash (-t > sets the TOS byte; -t 1 ends up as ECT(0) on the wire and -t 2 is > ECT(1)): > > $ traceroute -q 1 --sport=1 104.24.125.13 -t 1 > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > 1 _gateway (10.42.3.1) 0.336 ms > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 6.964 ms > 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.056 ms > 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.512 ms > 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.313 ms > 6 104.24.125.13 (104.24.125.13) 1.210 ms > > $ traceroute -q 1 --sport=1 104.24.125.13 -t 2 > traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets > 1 _gateway (10.42.3.1) 0.339 ms > 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 2.565 ms > 3 customer-185-24-168-38.ip4.gigabit.dk (185.24.168.38) 1.301 ms > 4 10ge1-2.core1.cph1.he.net (216.66.83.101) 1.339 ms > 5 be2306.ccr42.ham01.atlas.cogentco.com (130.117.3.237) 6.570 ms > 6 149.6.142.130 (149.6.142.130) 6.888 ms > 7 104.24.125.13 (104.24.125.13) 1.785 ms > > > So why is this a problem? The TCP SYN packet first needs to negotiate > ECN, so it is sent without any ECN bits set in the he
Re: ECN
> Hello > > I have a customer that believes my network has a ECN problem. We do > not, we just move packets. But how do I prove it? > > Is there a tool that checks for ECN trouble? Ideally something I could > run on the NLNOG Ring network. > > I believe it likely that it is the destination that has the problem. Hi Baldur I believe I may be that customer :) First of all, thank you for looking into the issue! We've been having great fun over on the ecn-sane mailing list trying to figure out what's going on. I'll summarise below, but see this thread for the discussion and debugging details: https://lists.bufferbloat.net/pipermail/ecn-sane/2019-November/000527.html The short version is that the problem appears to come from a combination of the ECMP routing in your network, and Cloudflare's heavy use of anycast. Specifically, a router in your network appears to be doing ECMP by hashing on the packet header, *including the ECN bits*. This breaks TCP connections with ECN because the TCP SYN (with no ECN bits set) end up taking a different path than the rest of the flow (which is marked as ECT(0)). When the destination is anycasted, this means that the data packets go to a different server than the SYN did. This second server doesn't recognise the connection, and so replies with a TCP RST. To fix this, simply exclude the ECN bits (or the whole TOS byte) from your router's ECMP hash. For a longer exposition, see below. You should be able to verify this from somewhere else in the network, but if there's anything else you want me to test, do let me know. Also, would you mind sharing the router make and model that does this? We're trying to collect real-world examples of network problems caused by ECN and this is definitely an interesting example. -Toke The long version: >From my end I can see that I have two paths to Cloudflare; which is taken appears to be based on a hash of the packet header, as can be seen by varying the source port: $ traceroute -q 1 --sport=1 104.24.125.13 traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets 1 _gateway (10.42.3.1) 0.357 ms 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 4.707 ms 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.283 ms 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.667 ms 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.406 ms 6 104.24.125.13 (104.24.125.13) 1.322 ms $ traceroute -q 1 --sport=10001 104.24.125.13 traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets 1 _gateway (10.42.3.1) 0.293 ms 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 3.430 ms 3 customer-185-24-168-38.ip4.gigabit.dk (185.24.168.38) 1.194 ms 4 10ge1-2.core1.cph1.he.net (216.66.83.101) 1.297 ms 5 be2306.ccr42.ham01.atlas.cogentco.com (130.117.3.237) 6.805 ms 6 149.6.142.130 (149.6.142.130) 6.925 ms 7 104.24.125.13 (104.24.125.13) 1.501 ms This is fine in itself. However, the problem stems from the fact that the ECN bits in the IP header are also included in the ECMP hash (-t sets the TOS byte; -t 1 ends up as ECT(0) on the wire and -t 2 is ECT(1)): $ traceroute -q 1 --sport=1 104.24.125.13 -t 1 traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets 1 _gateway (10.42.3.1) 0.336 ms 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 6.964 ms 3 customer-185-24-168-46.ip4.gigabit.dk (185.24.168.46) 1.056 ms 4 te0-1-1-5.rcr21.cph01.atlas.cogentco.com (149.6.137.49) 1.512 ms 5 netnod-ix-cph-blue-9000.cloudflare.com (212.237.192.246) 1.313 ms 6 104.24.125.13 (104.24.125.13) 1.210 ms $ traceroute -q 1 --sport=1 104.24.125.13 -t 2 traceroute to 104.24.125.13 (104.24.125.13), 30 hops max, 60 byte packets 1 _gateway (10.42.3.1) 0.339 ms 2 albertslund-edge1-lo.net.gigabit.dk (185.24.171.254) 2.565 ms 3 customer-185-24-168-38.ip4.gigabit.dk (185.24.168.38) 1.301 ms 4 10ge1-2.core1.cph1.he.net (216.66.83.101) 1.339 ms 5 be2306.ccr42.ham01.atlas.cogentco.com (130.117.3.237) 6.570 ms 6 149.6.142.130 (149.6.142.130) 6.888 ms 7 104.24.125.13 (104.24.125.13) 1.785 ms So why is this a problem? The TCP SYN packet first needs to negotiate ECN, so it is sent without any ECN bits set in the header; after negotiation succeeds, the data packets will be marked as ECT(0). But because that becomes part of the ECMP hash, those packets will take another path. And since the destination is anycasted, that means they will also end up at a different endpoint. This second endpoint won't recognise the connection, and reply with a TCP RST. This is clearly visible in tcpdump; notice the different TOS values, and that the RST packet has a different TTL than the SYN-ACK: 12:21:47.816359 IP (tos 0x0, ttl 64, id 25687, offset 0, flags [DF], proto TCP (6), length 60) 10.42.3.130.34420 > 104.24.125.13.80: Flags [SEW], cksum 0xf2ff (incorrect -> 0x0853), seq 3345293502, wi
Re: ECN
> On Nov 11, 2019, at 05:01 , Baldur Norddahl wrote: > > Hello > > I have a customer that believes my network has a ECN problem. We do not, we > just move packets. But how do I prove it? Are you saying that none of your routers support ECN or that you think ECN only applies to endpoints? > Is there a tool that checks for ECN trouble? Ideally something I could run on > the NLNOG Ring network. > > I believe it likely that it is the destination that has the problem. I’d say start with asking the reporter to provide a PCAP of the problem and review the packet trace to provide clues of tap points in your network to investigate where ECN is (or should be) occurring and the opposite is occurring. Owen
ECN
Hello I have a customer that believes my network has a ECN problem. We do not, we just move packets. But how do I prove it? Is there a tool that checks for ECN trouble? Ideally something I could run on the NLNOG Ring network. I believe it likely that it is the destination that has the problem. Regards, Baldur
Re: ECN, DNS and Firewalls
> On 28 Dec 2018, at 2:49 pm, valdis.kletni...@vt.edu wrote: > > On Fri, 28 Dec 2018 13:35:04 +1100, Mark Andrews said: >> There are major operators that still have STUPID firewall settings >> in front of DNS servers that drop SYN packets with ECE and CWR set >> 17 years after ECN was specified. > > Time to name-n-shame? No yet. Let people test and fix their firewalls first. A test machine should be sending [SEW] and getting back [S.E] or [S.] in the TCP flags using tcpdump depending upon whether the DNS server’s TCP stack supports ECN or not. e.g. 11:35:50.335713 IP6 2001:470:a001:3:f1f2:b12d:4b18:d934.50670 > 2001:7fe::53.53: Flags [SEW], seq 3764146938, win 65535, options [mss 1220,nop,wscale 5,nop,nop,TS val 522561237 ecr 0,sackOK,eol], length 0 11:35:50.745472 IP6 2001:7fe::53.53 > 2001:470:a001:3:f1f2:b12d:4b18:d934.50670: Flags [S.E], seq 1542147586, ack 3764146939, win 14280, options [mss 1440,sackOK,TS val 1392826170 ecr 522561237,nop,wscale 7], length 0 or 11:40:35.360655 IP6 2001:470:a001:3:f1f2:b12d:4b18:d934.50697 > 2001:502:8cc::30.53: Flags [SEW], seq 81498720, win 65535, options [mss 1220,nop,wscale 5,nop,nop,TS val 522845405 ecr 0,sackOK,eol], length 0 11:40:35.589420 IP6 2001:502:8cc::30.53 > 2001:470:a001:3:f1f2:b12d:4b18:d934.50697: Flags [S.], seq 987294478, ack 81498721, win 1220, options [mss 1220], length 0 Mark -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org
Re: ECN, DNS and Firewalls
On Fri, 28 Dec 2018 13:35:04 +1100, Mark Andrews said: > There are major operators that still have STUPID firewall settings > in front of DNS servers that drop SYN packets with ECE and CWR set > 17 years after ECN was specified. Time to name-n-shame?
ECN, DNS and Firewalls
There are major operators that still have STUPID firewall settings in front of DNS servers that drop SYN packets with ECE and CWR set 17 years after ECN was specified. Do you really want to add a second to EVERY DNS lookup that needs to use TCP? Modern OS actually attempt to use ECN by default. DNS is time critical enough without introducing unnecessary delays. If you have signed zones then TCP requests are almost certainly being made to your servers. EVERYONE TEST YOUR SERVERS FROM OUTSIDE YOUR NETWORK AND FIX THE BROKEN FIREWALLS THAT ARE FOUND. -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org
Re: Apple ECN, Bufferbloat, CoDel (fwd)
On Sat, Jun 13, 2015 at 06:20:31PM +0200, Mikael Abrahamsson wrote: Hi, I just want to bring to your attention the below talk (I am too lazy to re-write the whole email for this slightly different audience). Takeaway: We'll see a lot of ECN enabled traffic in a few months. This shouldn't be a problem. I've been doing it to all my machines for 3-5 years without ill effects. I recall when ECN first came out and firewalls would block it causing me issues on my Linux boxes sending list mail out. It was a small enough percentage that I mostly ignored it, but this will cause trouble for people who still haven't fixed their broken firewalls. I encourage almost everyone on nanog to watch this talk. - Jared -- Forwarded message -- Date: Sat, 13 Jun 2015 18:07:57 +0200 (CEST) From: Mikael Abrahamsson swm...@swm.pp.se To: bl...@lists.bufferbloat.net Subject: Apple ECN, Bufferbloat, CoDel I highly encourage people to take a look at: https://developer.apple.com/videos/wwdc/2015/?id=719 -- Mikael Abrahamssonemail: swm...@swm.pp.se -- Jared Mauch | pgp key available via finger from ja...@puck.nether.net clue++; | http://puck.nether.net/~jared/ My statements are only mine.
Re: Apple ECN, Bufferbloat, CoDel (fwd)
On Mon, Jun 15, 2015 at 9:13 AM, joel jaeggli joe...@bogus.com wrote: On 6/15/15 6:19 AM, Jared Mauch wrote: On Sat, Jun 13, 2015 at 06:20:31PM +0200, Mikael Abrahamsson wrote: Hi, I just want to bring to your attention the below talk (I am too lazy to re-write the whole email for this slightly different audience). Takeaway: We'll see a lot of ECN enabled traffic in a few months. This shouldn't be a problem. I've been doing it to all my machines for 3-5 years without ill effects. you'll also find all the networks that use the entire tos field as part of the hash key... that's not exactly something you notice when you have a 1:1 host to ip correspondence unless it leads to reordering. but with stateless load balancing you can. fortunately those networks are observably rare. I am aware of one such (very large) network that did, indeed, (and til recently!) have devices that used the entire tos field in their ECMP implementation. This led to re-ordering every time ECN CE was exerted on ECN enabled flows. Testing for the existence of this problem is not terribly hard (example, have a rule that periodically exerts CE on a bunch of test tcp flows, count the reorders in TCP_INFO), but the tools for it are kind of adhoc as yet. I am curious if there is a SNMP mib/cacti/mrtg/other support for reporting CE events in addition to loss? Although fq_codel and pie (as deployed in linux - sadly docis-pie has no ECN support in the spec) do do ecn markings (fq_codel *by default*), deployment on bottleneck links is limited as yet. :) My expectation is that this will make a difference first for apple streaming video apps in the home, connecting to other devices in the home (over wifi, ethernet, bluetooth, etc) that will start to make use of this additional signalling information. And a billion new devices with ecn on by default will probably expose all the other problems rather rapidly. ;) I recall when ECN first came out and firewalls would block it causing me issues on my Linux boxes sending list mail out. It was a small enough percentage that I mostly ignored it, but this will cause trouble for people who still haven't fixed their broken firewalls. Better fallbacks exist now. I encourage almost everyone on nanog to watch this talk. - Jared -- Forwarded message -- Date: Sat, 13 Jun 2015 18:07:57 +0200 (CEST) From: Mikael Abrahamsson swm...@swm.pp.se To: bl...@lists.bufferbloat.net Subject: Apple ECN, Bufferbloat, CoDel I highly encourage people to take a look at: https://developer.apple.com/videos/wwdc/2015/?id=719 -- Mikael Abrahamssonemail: swm...@swm.pp.se -- Dave Täht What will it take to vastly improve wifi for everyone? https://plus.google.com/u/0/explore/makewififast
Re: Apple ECN, Bufferbloat, CoDel (fwd)
On 6/15/15 6:19 AM, Jared Mauch wrote: On Sat, Jun 13, 2015 at 06:20:31PM +0200, Mikael Abrahamsson wrote: Hi, I just want to bring to your attention the below talk (I am too lazy to re-write the whole email for this slightly different audience). Takeaway: We'll see a lot of ECN enabled traffic in a few months. This shouldn't be a problem. I've been doing it to all my machines for 3-5 years without ill effects. you'll also find all the networks that use the entire tos field as part of the hash key... that's not exactly something you notice when you have a 1:1 host to ip correspondence unless it leads to reordering. but with stateless load balancing you can. fortunately those networks are observably rare. I recall when ECN first came out and firewalls would block it causing me issues on my Linux boxes sending list mail out. It was a small enough percentage that I mostly ignored it, but this will cause trouble for people who still haven't fixed their broken firewalls. I encourage almost everyone on nanog to watch this talk. - Jared -- Forwarded message -- Date: Sat, 13 Jun 2015 18:07:57 +0200 (CEST) From: Mikael Abrahamsson swm...@swm.pp.se To: bl...@lists.bufferbloat.net Subject: Apple ECN, Bufferbloat, CoDel I highly encourage people to take a look at: https://developer.apple.com/videos/wwdc/2015/?id=719 -- Mikael Abrahamssonemail: swm...@swm.pp.se signature.asc Description: OpenPGP digital signature
Apple ECN, Bufferbloat, CoDel (fwd)
Hi, I just want to bring to your attention the below talk (I am too lazy to re-write the whole email for this slightly different audience). Takeaway: We'll see a lot of ECN enabled traffic in a few months. This shouldn't be a problem. I've been doing it to all my machines for 3-5 years without ill effects. More people will become interested in how TCP works, from application, through the host stack, to the AQM (or lack thereof) in the router etc. If you don't do AQM towards your customers, be prepared that they're going to start complaining in a more informed manner in the not so distant future. IPv6 only with NAT64+DNS64 will become a lot more feasible going forward. I am not a fan of breaking DNSSEC, but perhaps if we can do the DNS64 in the host (as it seems Apple is doing, at least for IPv4 literals), then that might be possible to work around. -- Forwarded message -- Date: Sat, 13 Jun 2015 18:07:57 +0200 (CEST) From: Mikael Abrahamsson swm...@swm.pp.se To: bl...@lists.bufferbloat.net Subject: Apple ECN, Bufferbloat, CoDel I highly encourage people to take a look at: https://developer.apple.com/videos/wwdc/2015/?id=719 (you might have to reigster as an apple developer to watch it, I don't know) Your App and Next Generation Networks IPv6 is growing exponentially and carriers worldwide are moving to pure IPv6 APNs. Learn about new tools to test your apps for compatibility and get expert advice on making sure your apps work in all network environments. iOS 9 and OS X 10.11 now support the latest TCP standards. Hear from the experts on TCP Fast Open and Explicit Congestion Notification, and find out how it benefits your apps. Being on this list you might not learn much from the talk, but I really appreciate a talk aimed at a wider (developer) audience which so clearly outlines the benefits of ECN, CoDel and TCP host opimization to reduce end-to-end experienced application communication latency. One of the major takeaways is that Apple is planning to by default enable ECN in iOS9 and OSX 10.11. This would mean hundreds of millions of devices will be using ECN in a few months. You can skip to 16 minutes into the talk if you're not interested in the new requirement for applications to support an environment where it's Internet access is IPv6 only behind NAT64+DNS64 (I'm myself super excited about this). Let's hope this brings a lot of buzz and requests towards device manufacturers to start supporting ECN marking and AQM. Apple is usually a good megaphone to bring attention to these kinds of issues... -- Mikael Abrahamssonemail: swm...@swm.pp.se
Re: ECN
On Fri, 7 Nov 2008, [EMAIL PROTECTED] wrote: On Fri, 07 Nov 2008 08:27:58 +0100, Mikael Abrahamsson said: for ECN to actually be useful, we (the ISPs) have to turn this option on in the routers as well. Is anyone doing this today? What vendors support it? The only thing that's *required* for it to help is that the routers and firewalls not actually *molest* the bits in the TCP SYN packet. If you pass them and *do nothing else*, it at least has the potential of being useful at some other router along the path. And let's face it - if *your* router is congested enough for ECN to matter, there's a fairly good chance that the router one hop up/downstream is *also* seeing some effects. Even if *you* don't do anything else, your neighbor might - helping you out in the bargain. See: http://www.icir.org/floyd/ecn.html http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ftwrdecn.html -Hank
Re: ECN
When I thought about it, the IP core (10G links etc) first came to mind, and there it's fairly easy to roll out (since I guess a lot of us do WRED already), but what about on slower links? Would it make sense to have our DSLAMs do this? What about DSL/cable modems (well, vendors should first realise that FIFO is not great to begin with :P) ? Implementing this in an MPLS core is not an easy task, you can really only do this on the edge, when the MPLS labelled packet arrives at an LSR, we don't know if it contains a TCP segment or not (fancy deep h/w implementations excluded), all we know is that , if there is congestion, we can discard it based on the EXP bits in the shim. Dave.
Re: ECN
David Freedman [EMAIL PROTECTED] writes: Implementing this in an MPLS core is not an easy task, you can really only do this on the edge, when the MPLS labelled packet arrives at an LSR, we don't know if it contains a TCP segment or not (fancy deep h/w implementations excluded), all we know is that , if there is congestion, we can discard it based on the EXP bits in the shim. Please see RFC 5129 Bjørn
Re: ECN
Interesting , I hadn't followed this since draft-ietf-mpls-ecn-00, , I eagerly await a vendor implementation :) Dave. Bjørn Mork wrote: David Freedman [EMAIL PROTECTED] writes: Implementing this in an MPLS core is not an easy task, you can really only do this on the edge, when the MPLS labelled packet arrives at an LSR, we don't know if it contains a TCP segment or not (fancy deep h/w implementations excluded), all we know is that , if there is congestion, we can discard it based on the EXP bits in the shim. Please see RFC 5129 Bjørn
Re: ECN
On Fri, 7 Nov 2008, David Freedman wrote: Implementing this in an MPLS core is not an easy task, you can really only do this on the edge, when the MPLS labelled packet arrives at an LSR, we don't know if it contains a TCP segment or not (fancy deep h/w implementations excluded), all we know is that , if there is congestion, we can discard it based on the EXP bits in the shim. I did some more checking and neither 12000 (IOS) nor CRS-1 seems to support WRED with ECN (at least the command doesn't show when I create a policy-map), so I'm going to ping my Cisco SE and hear about what's going on. -- Mikael Abrahamssonemail: [EMAIL PROTECTED]
Re: ECN
On Fri, 07 Nov 2008 08:27:58 +0100, Mikael Abrahamsson said: for ECN to actually be useful, we (the ISPs) have to turn this option on in the routers as well. Is anyone doing this today? What vendors support it? The only thing that's *required* for it to help is that the routers and firewalls not actually *molest* the bits in the TCP SYN packet. If you pass them and *do nothing else*, it at least has the potential of being useful at some other router along the path. And let's face it - if *your* router is congested enough for ECN to matter, there's a fairly good chance that the router one hop up/downstream is *also* seeing some effects. Even if *you* don't do anything else, your neighbor might - helping you out in the bargain. pgpWRdhiL6ucT.pgp Description: PGP signature
ECN
Hi, On LKML (Linux Kernel Mailing List) there is talk http://lkml.org/lkml/2008/11/4/151 about shipping the Linux kernel with ECN turned on by default (it was on by default a few years back but that change was reverted due to too many sites dropping ECN enabled SYNs). Recent investigations http://www.imperialviolet.org/binary/ecntest.pdf shows that 0.5% of end hosts will drop SYN packets with ECN turned on. This is approximately the same rate I have seen for A/ adoption in this tread http://www.ops.ietf.org/lists/v6ops/v6ops.2008/msg01585.html. Do we in the operational ISP community have an opinion on ECN adoption that we want to voice? As far as I can discern from http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ftwrdecn.html for ECN to actually be useful, we (the ISPs) have to turn this option on in the routers as well. Is anyone doing this today? What vendors support it? When I thought about it, the IP core (10G links etc) first came to mind, and there it's fairly easy to roll out (since I guess a lot of us do WRED already), but what about on slower links? Would it make sense to have our DSLAMs do this? What about DSL/cable modems (well, vendors should first realise that FIFO is not great to begin with :P) ? http://www.icir.org/tbit/ is a summary page I found on ECN that looks like a good resource for further reading. Is anyone looking into including ECN configuration into some BCP document? -- Mikael Abrahamssonemail: [EMAIL PROTECTED]
