On Tue, Dec 21, 2021 at 6:24 AM Templin (US), Fred L <fred.l.temp...@boeing.com> wrote: > > Tom, reading your message makes me think you have not read my drafts. The > > answers to the perceived issues you are raising are all there. I do not see > anything > > new in what you are saying to make me believe otherwise. > >
Fred, I did read your draft. I might be misunderstanding it. Here are points I don't think I understand, f these are in the draft plead reference the precise section: - A clear explanation why GSO/GRO are not sufficient to solve the problem. The draft highlights these to show the advantages of sending/receiving large data units, but it's not clear to me why a change to the protocol is required to get the same or somehow better effect. As a side note, it should be pointed out that GSO/GRO and similar mechanisms are opportunistic optimizations. For instance, the TCP congestion window and receive window have to be large enough for GSO to be effective for sending on a connection. As an anecdote, there was an incident early on at YouTube where they extensively used GSO for serving video which under normal circumstances is a great savings in CPU utilization. But one day there was a hiccup on the Internet that caused all the connections to go to slow start. So now instead of sending 64K at a time the servers were sending two segments at a time for all the connections (this was before the work to raise initcwnd); so now instead of servers running at 50% CPU, they needed 150% CPU and so were dropping a lot of packets, and recovering took quite a bit of time making unhappy customers (moral of this story: always provision your servers to handle the worst case scenario where opportunistic optimizations become ineffective!) - What is the exact algorithm for reassembly of parcels? Searching the document for reassemble only comes up with "when the OAL source or final destination receives the fragments or whole parcels, it reassembles if necessary" - What are the ramifications of middleboxes performing reassembly on behalf of a host. The document says "then rejoined into one or more parcels at a last-hop middlebox to be forwarded to the final destination". I'm not sure what a "last-hop middlebox" means in a normative context, but this does appear to be an intermediate network node which would seem to be susceptible to the issues of stateful intermediate network nodes that I previously raised. - Is in order delivery of segments within a parcel maintained. The draft states "While not desirable, reordering of segments within parcels and individual segment loss are possible. But, what matters is that the number of parcels delivered to the final destination should be kept to a minimum, and that loss or receipt of individual segments (and not parcel size) determines the retransmission unit". Why is it so critical to keep the number of parcels delivered to the final destination to be kept at minimum? As I mentioned, hosts are already used to dealing with reassembly, it seems like the best method is still to send packets at path MTU which is what TCP is doing with PMTUD. - How are IP parcels substantially different from fragmentation? Is the idea that individual segments in an IP parcel can be lost without losing the whole parcel? Is the idea that parcels can make up a >64K super packet? What if a segment in a parcel is greater than an MTU in the path, is an intermediate node breaking up a parcel expected to fragment the segment, or send a PTB? Tom > > Thanks - Fred > > > > From: Tom Herbert [mailto:t...@herbertland.com] > Sent: Monday, December 20, 2021 4:14 PM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: to...@strayalpha.com; int-area@ietf.org > Subject: Re: IP parcels > > > > > > On Mon, Dec 20, 2021 at 3:11 PM Templin (US), Fred L > <fred.l.temp...@boeing.com> wrote: > > Tom, in modern reassembly it is not going to wait for the MSL for all > fragments > > to arrive anymore; either they all get there after a very small inter-fragment > > delay, or you send an immediate FRAGREP and possibly also a PTB soft error > > then quickly declare the reassembly dead if that doesn’t help. And, you make > > sure to inspect IDs of received fragments before admitting them into the > > reassembly cache so you don’t end up caching garbage that will just have to > > be discarded later. > > > > Fred, > > > > It doesn't matter in the sense that reassembly is a non-working conserving > mechanism. In order to perform reassembly packet fragments need to be held > which means memory will be consumed and since memory is a finite resource it > needs to be managed. Managing memory means that some policy is needed when > to time out a reassembly or which fragment train to discard under memory > pressure. A network that implements some arbitrary policy can cause problems > on unsuspecting hosts. For instance, there's mechanisms for hosts to try to > guess what the timeout is in a NAT box and send a keepalive packet before an > idle NAT state is evicted. So this is just a guess that may or may not be > right, and in fact there might not even be a NAT in the path in which case > the host is just wasting energy sending keepalives. Also, the second we > introduce a new exhaustible resource in the path that becomes yet another > denial of service vector (consider the case that an attacker spoofs a whole > bunch of IP parcels). > > > > Unless the network can coordinate very specifically with the host about what > it's doing on behalf of the host stack, I think it's much better for the > network to just focus or forward packets without delay and let the host > handle the details of receive processing, reassembly, security, etc. > > > > Tom > > > > > > Fred > > > > From: Tom Herbert [mailto:t...@herbertland.com] > Sent: Monday, December 20, 2021 1:06 PM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: to...@strayalpha.com; int-area@ietf.org > Subject: Re: IP parcels > > > > > > On Mon, Dec 20, 2021 at 12:03 PM Templin (US), Fred L > <fred.l.temp...@boeing.com> wrote: > > Tom, sorry I will try to use my words more carefully; I am using GSO/GRO also > for > > a UDP-based transport protocol – not QUIC but something similar. I like > GSO/GRO > > very much; I am glad the service is available and I want to see it continue. > But, my > > understanding of the services is that they leverage the IP ID field in whole > IPv4 > > packets that are not eligible for fragmentation and those are limitations I am > > seeking to improve on. > > > > I want to enable a facility similar to GSO/GRO that works for both IPv4 and > IPv6 > > packets and allows for lower layers to fragment if necessary. And, I want to > use > > a well-behaved 32-bit IPv6 ID instead of the 16-bit IPv4 one where the use is > not > > well defined when DF=1. > > > > There has been a lot of work in this area. For instance, you might want to > take a look at https://www.youtube.com/watch?v=ccUeG1dAhbw > > > > About reassembly, that would only happen on the end systems themselves or on > > a very capable device that is very close to the end systems; I would not want > for > > a high-speed core router to have to reassemble. > > > > Even so, an intermediate device close to the end system still has to provide > service to more than one host. Reassembly requires memory to store fragments. > A host would need enough memory to service all of its own flows, but an > intermediate node would need number of hosts it serves times that amount of > memory to perform reassembly. This is a fundamental scaling problem of > stateful services in the network, inevitably the network nodes cannot scale > to the number of users or flows that require service. In the best case > scenario, when resources are not available the network won't attempt the > stateful operation and will just forward the packet unimpeded (which is fine > because host will never rely on this class of optimization). In the worse > case scenario, the network will take a detrimental action such as forcibly > breaking a connection (e.g. this is what can happen when a NAT evicts a TCP > connection because it has run out of memory). IMO, maintaining state in the > network is a bad, albeit unfortunately prevalent, idea. > > > > Tom > > > > > > Again, GSO/GRO is nice work and much respect is due to those who made it > possible. > > > > Fred > > > > From: Tom Herbert [mailto:t...@herbertland.com] > Sent: Monday, December 20, 2021 9:20 AM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: to...@strayalpha.com; int-area@ietf.org > Subject: Re: [Int-area] [EXTERNAL] Re: IP parcels > > > > The world is not just TCP anymore. QUIC and other UDP-based transports have > already > > shown performance increases using facilities like GSO/GRO which are > essentially a short > > term and non-standard implementation of what parcels promise to do in the > long term. > > > > Fred, > > > > Can you explain why GSO/GRO aren't sufficient and are only short term > solutions? We've been using these for almost twenty years now with good > effect. These are widely deployed with TCP, TSO works well to offload > transmit, LRO is defined and is in much better shape to offload RX now that > programmable devices are emerging. For TCP it's hard to see how IP parcels > would help significantly, but even for UDP we now have UDP GSO, sendmmsg, and > recvmmsg that mitigate the cost of system calls and interrupts to which the > draft refers. The reason these aren't standards in IETF is because they're > implementation techniques and not protocol (although I will point out that > GSO/GRO/sendmmsg/recvmmsg are in all Linux devices so that effectively makes > it a de facto implementation standard). > > > > I am also concerned about the idea that intermediate devices would perform > reassembly. This has a whole bunch of implications like middleboxes are no > longer work conserving and seems to have the implicit requirement that it has > to be in the path of every packet in a parcel (i.e. even in the case of the > last hop performing reassembly. Also, as simply a matter of resources and > capabilities, hosts are in a much better position to perform tasks like > reassembly. I don't readily see that having intermediate devices perform > reassembly would be a win for hosts, and even if it were, host > implementations still would need the capability to perform reassembly > themselves since they will never rely on the network to always do it for them. > > > > Tom > > > > > > Thanks - Fred > > > > From: to...@strayalpha.com [mailto:to...@strayalpha.com] > Sent: Sunday, December 19, 2021 11:53 AM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: int-area@ietf.org; Wes Eddy <w...@mti-systems.com> > Subject: Re: [Int-area] IP parcels > > > > Hi, Fred (et al.), > > > > On Dec 19, 2021, at 10:21 AM, Templin (US), Fred L > <fred.l.temp...@boeing.com> wrote: > > > > Joe, your insistence on using html makes it impossible to respond to all of > your points inline > > which is the reason for my top-posts. > > > > I use MacOS mail, IOS mail, and Thunderbird on Windows, all using default > configurations, FWIW. I appear to be able to post inside everyone else’s > responses. I don’t know if the IETF’s mailers are munging formats, though. > > > > I’ve made my position clear. However: > > > > - You still haven’t shown any evidence that end systems need to do all this > extra work so they can somehow run faster, nor that this will be noticeably > faster than large (i.e., 20-60KB) IPv4 packets. > > > > - You still haven’t shown any reason why this is feasible; in fact, below you > add the idea of on-path fragmentation, which is largely deprecated because > fragments won’t traverse tunnels (in your case, notably for single chunks > larger than 64KB). Nevermind that the fragmentation is both expensive and > slow-path at routers. > > > > - You have claimed that both routers and transports will somehow adopt this > when we can’t even get reasonably large MTUs that already fit within IPv4 > across heterogeneous enterprises. > > > > IPv4 is over; even if you don’t think so, any way forward with larger packets > starts with: > > a) getting ~64KB IP packets across the net > > b) after (a), prove that >64KB are needed based on the IPv6 > jumbo approach > > > > Any way forward with a lot of small packets inside one large one (where both > chunks and total length are less than 64K) starts by proving there’s a need > and it fixing how TCP interacts with its inherent burstiness and loss > correlation. > > > > Only THEN will this issue be worth more discussion. > > > > Joe > > > > > > Parcels that contain a single segment whether 64K or considerably less are > still sent as > > (singleton) parcels and not ordinary packets. That way, nodes in the network > can know > > that it is OK to encapsulate and fragment since by asserting its interest in > receiving parcels > > the destination has also subscribed to being able to reassemble up to a full > 64K. > > > > Parcels do not set (Payload Length / Total Length) to 0; they set it to the > length of the > > first element of the parcel (which is also the same length of each non-final > element of > > the parcel). What happens then is that network equipment will see a unit with > an L3 > > length that may be considerably shorter than the L2 length. You are right > that legacy > > routers might not like this (or, they might truncate the packet according to > L3 length), > > and so for paths that might traverse legacy routers the first-hop node that > recognizes > > parcels instead encapsulates the parcel in an IPv4 or IPv6 header then > performs (source) > > fragmentation if necessary. These IP fragments will then travel through > legacy routers > > just fine. > > > > About RFC793bis, you and Wes Eddy know far more about its status than I do; I > only > > noted that this is something with TCP implications and so made mention of it > in case > > there is still room for a few more engine tweaks while the hood is still open. > > > > About IPv4, I am currently running IPv4 edge networks with IPv4-in-IPv6 > tunnel endpoints > > connected to an IPv6 transit network and it works really good. End systems > get to use > > smaller addresses and smaller headers, and they can talk to remote > correspondents using > > IPv4 as if they were all on the same IPv4 network. So yes, I think we might > still want to > > consider IPv4 for edge networks like that. > > > > About getting 64K packets across, only the edge networks or end systems see > them as > > large packets; in the core thy are typically broken up into something much > smaller by > > ingress nodes that apply segmentation/fragmentation. We don’t need the core > to move > > to jumbo links; we only need that at the edges. ATM taught us that. > > > > About our “nail”, end systems get to see larger packets/parcels and get to > take advantage > > of the reduced interrupts and system call overhead they provide. That is what > makes it > > worthwhile. > > > > Fred > > > > From: to...@strayalpha.com [mailto:to...@strayalpha.com] > Sent: Saturday, December 18, 2021 8:13 PM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: int-area@ietf.org; Wes Eddy <w...@mti-systems.com> > Subject: Re: [Int-area] IP parcels > > > > HI, Fred, > > > > If you have one segment that’s less than 64K, you don’t need the parcel > option at all. > > > > If you have something longer than 64K, either as a single segment or multiple > smaller segments, by setting total length to 0, you end up being dropped by > legacy routers, which either ignore options they don’t understand or drop > packets with options they don’t support. > > > > RFC793bis does talk about IPv6 jumbos, but this new work is out of scope for > RFC793bis - furthermore, it’s too late. It has passed WGLC, IETF LC, and is > currently in IESG review for publication. > > > > You also haven’t addressed why the IETF should be taking up this *new* work > for IPv4, which I thought also had been considered ineligible. > > > > But overall, again, what’s the point? We can’t even get 64K IP packets > through the Internet; making them larger doesn’t make that easier or more > likely. Such large sizes are of diminishing benefit; routers already forward > at 40Gbps per link for minimal packets and end systems have other problems > that this exacerbates. > > > > This seems a lot like a huge hammer in search of a nail. Where’s the nail? > > > > Joe > > > > — > > Joe Touch, temporal epistemologist > > www.strayalpha.com > > > > On Dec 18, 2021, at 7:18 PM, Templin (US), Fred L <fred.l.temp...@boeing.com> > wrote: > > > > Joe, I never said that I wanted to restrict this to small transport segments; > in fact, I want > > just the opposite – I want large segments. A perfectly legal parcel is one > which includes 1 > > ~64KB segment - another legal parcel is one which includes 64 of them! If you > want bigger > > segments than that, then true jumbos are necessary and this spec does not > preclude that. > > > > About RFC793(bis), I see there is a section on Jumbos and IP parcels is (sort > of) an application > > of Jumbos. > > > > Fred > > > > From: to...@strayalpha.com [mailto:to...@strayalpha.com] > Sent: Saturday, December 18, 2021 4:57 PM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: int-area@ietf.org; Wes Eddy <w...@mti-systems.com> > Subject: [EXTERNAL] Re: [Int-area] IP parcels > > > > EXT email: be mindful of links/attachments. > > > > > Hi, Fred, > > > > Regarding 793bis, new ideas are out of scope. It’s supposed to be a roll-in > of existing items only. > > > > Nevermind the problems below, which “TCP will find a way” doesn’t magically > fix. > > > > The problem is this: > > - end systems need to send larger transport segments (not just IP segments) > > - if they can do that, they should, filling up to the largest IP payload > > > > Having an IP packet have the opportunity to include lots of small transport > packets assumes transport packets either work better or faster when they’re > small. It’s the opposite. > > > > Joe > > > > — > > Joe Touch, temporal epistemologist > > www.strayalpha.com > > > > On Dec 18, 2021, at 4:42 PM, Templin (US), Fred L <fred.l.temp...@boeing.com> > wrote: > > > > Joe, TCP will find a way to adapt – it always has. I also see that TCP is > currently undergoing > > a second edition revision so the timing seems right to consider IP parcels in > the analysis. > > I am Cc’ing the second edition editor for his information – Wesley, please > consider this > > new concept called “IP Parcels” as it relates to your document. > > > > Here is the latest draft version – it expands on the “Motivation” section and > adds a number > > of important feature such as a new “Parcels Permitted” TCP option: > > > > https://datatracker.ietf.org/doc/draft-templin-intarea-parcels/ > > > > Fred > > > > From: to...@strayalpha.com [mailto:to...@strayalpha.com] > Sent: Friday, December 17, 2021 6:01 PM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: int-area@ietf.org > Subject: Re: [Int-area] IP parcels > > > > Hi, Fred, > > > > I’m first concerned at the use of an IP option at all, due to the problems > with *any* options forcing processing to slow-path. > > > > From TCP’s viewpoint, it seems like you’ve just created a nightmare for SACK > and ECN, basically because you will encourage drops of large bursts of > packets. > > > > This will also increase the bustiness of TCP, i.e., rather than letting the > ACKs support pacing. > > > > Any part of the system that currently coalesces TCP packets is likely to > generate errors here, because they might see only the first TCP segment. > > > > However, AFAICT the most significant consideration is that the issue with > per-packet performance is at the TCP and UDP layers, not as much at the IP > layer. > > > > So what problem is this trying to solve? > > > > Joe > > — > > Joe Touch, temporal epistemologist > > www.strayalpha.com > > > > On Dec 17, 2021, at 5:06 PM, Templin (US), Fred L <fred.l.temp...@boeing.com> > wrote: > > > > Here's one that should help with shipping, just in time for Christmas. Thanks > to everyone for the past and future list exchanges. > > Fred > > -----Original Message----- > From: I-D-Announce [mailto:i-d-announce-boun...@ietf.org] On Behalf Of > internet-dra...@ietf.org > Sent: Friday, December 17, 2021 5:00 PM > To: i-d-annou...@ietf.org > Subject: I-D Action: draft-templin-intarea-parcels-00.txt > > > A New Internet-Draft is available from the on-line Internet-Drafts > directories. > > > Title : IP Parcels > Author : Fred L. Templin > Filename : draft-templin-intarea-parcels-00.txt > Pages : 8 > Date : 2021-12-17 > > Abstract: > IP packets (both IPv4 and IPv6) are understood to contain a unit of > data which becomes the retransmission unit in case of loss. Upper > layer protocols such as the Transmission Control Protocol (TCP) > prepare data units known as "segments", with traditional arrangements > including a single segment per packet. This document presents a new > construct known as the "IP Parcel" which permits a single packet to > carry multiple segments. The parcel can be opened at middleboxes on > the path with the included segments broken out into individual > packets, then rejoined into one or more repackaged parcels to be > forwarded further toward the final destination. Reordering of > segments within parcels is unimportant; what matters is that the > number of parcels delivered to the final destination should be kept > to a minimum, and that loss or receipt of individual segments (and > not parcel size) determines the retransmission unit. > > > The IETF datatracker status page for this draft is: > https://datatracker.ietf.org/doc/draft-templin-intarea-parcels/ > > There is also an htmlized version available at: > https://datatracker.ietf.org/doc/html/draft-templin-intarea-parcels-00 > > > Internet-Drafts are also available by rsync at rsync.ietf.org::internet-drafts > > > _______________________________________________ > I-D-Announce mailing list > i-d-annou...@ietf.org > https://www.ietf.org/mailman/listinfo/i-d-announce > Internet-Draft directories: http://www.ietf.org/shadow.html > or ftp://ftp.ietf.org/ietf/1shadow-sites.txt > > _______________________________________________ > Int-area mailing list > Int-area@ietf.org > https://www.ietf.org/mailman/listinfo/int-area > > > > _______________________________________________ > Int-area mailing list > Int-area@ietf.org > https://www.ietf.org/mailman/listinfo/int-area _______________________________________________ Int-area mailing list Int-area@ietf.org https://www.ietf.org/mailman/listinfo/int-area
