On Mon, Nov 18, 2024 at 8:36 AM Templin (US), Fred L <Fred.L.Templin= 40boeing....@dmarc.ietf.org> wrote:
> Thank you, Tom. With GSO, upper layer protocols prepare a buffer that > contains the concatenation of N segments (N <= 64), each of which contains > upper layer protocol information allowing it to be processed independently > of the others. This multi-segment buffer (call it a “parcel buffer”) is > then presented to progressively lower layers until it reaches the ultimate > point of preparation for transmission over an Internetwork. At that point, > existing GSO implementations break the parcel buffer apart and transmit > each of the N segments as an individual IP packet through a process called > “packetization”. With IP parcels, however, the parcel buffer is kept > intact and a Parcel Integrity Block (PIB) is appended ahead of the buffer. > Next, a Parcel Payload Option (PPO) IP extension header is included, then > the entire parcel is transmitted over the Internetwork without first > applying packetization. > > > IP parcels therefore use exactly the same code as GSO up to the decision > point of whether to apply packetization or send as a whole IP parcel. At > that point, extra code is needed to append the PIB and PPO. Yes, this means > that a parcel will look different than an ordinary packet over the wire and > that the path must have a sufficiently large MTU, which is why the path > must first be probed to ensure all hops can support delivery. (Note, this > is only the send side consideration; an analogous sequence of events is > applied at the receive side according to GRO.) > HI Fred, So we need to do PMTU discovery and ensure that IP parcels don't exceed MTU size? Why not just report the PMTU to the application and let them send bigger packets if PMTU is greater than minimum MTU thereby avoiding complexities of additional on-the-wire protocol? TCP over UDP encapsulation would already work this way, and I imagine QUIC could be adapted to opportunistically send larger packets if that's not already supported. Also, GRO/GSO solve the problem of application sending or receiving greater than PMTU size "packets", so it's not clear to me how IP parcels helps either performance in the local stack or on the wire. Maybe I'm missing something... Tom > > > > Fred > > > > *From:* Tom Herbert <tom=40herbertland....@dmarc.ietf.org> > *Sent:* Saturday, November 16, 2024 12:06 AM > *To:* Templin (US), Fred L <fred.l.temp...@boeing.com> > *Cc:* C. M. Heard <he...@pobox.com>; Gorry Fairhurst <go...@erg.abdn.ac.uk>; > Joe Touch <to...@strayalpha.com>; int-area <int-area@ietf.org>; 6man < > i...@ietf.org>; TSVWG <ts...@ietf.org> > *Subject:* Re: [tsvwg] Re: UDP options [was IP Parcels and Advanced > Jumbos (AJs)] > > > > > > On Fri, Nov 15, 2024, 7:22 PM Templin (US), Fred L <Fred.L.Templin= > 40boeing....@dmarc.ietf.org> wrote: > > Tom, > > > > > Let me rephrase. Does the GRO/GSO implementation need to change because > of IP parcels? > > > > You are more qualified to answer this question than I am. > > > > Fred, > > > > I have some understanding of how GRO/GSO works today, but no idea what the > interaction would be with IP parcels. IMO, it's a matter of design and > implementation. > > > > A key design point of GRO/GSO is that there is no change to protocols and > in fact they're transparent on the wire. For UDP we can do GRO/GSO in two > modes: generic model collects UDP payloads into a single packet where the > application can deduce the individual datagrams (this is critical for QUIC > performance); we can also do TCP GRO/GSO when TCP is encapsulated in UDP > like VXLAN. > > > > IP parcels seems to be a significant change to the protocol, so I imagine > proper support for GRO/GSO needs to be implemented. Even before that, > understanding the interaction with checksum offload might be more pertinent. > > > > I'd also point out that the interaction with GRO/GSO and checksum offload > are also open questions for UDP Options, so it seems to me that trying to > define how IP parcels and UDP Options work together is a bit premature. I > think we need running code for each of them first. > > > > Tom > > > > > > *From:* Tom Herbert <tom=40herbertland....@dmarc.ietf.org> > *Sent:* Friday, November 15, 2024 10:43 AM > *To:* Templin (US), Fred L <fred.l.temp...@boeing.com> > *Cc:* C. M. Heard <he...@pobox.com>; Gorry Fairhurst <go...@erg.abdn.ac.uk>; > Joe Touch <to...@strayalpha.com>; int-area <int-area@ietf.org>; 6man < > i...@ietf.org>; TSVWG <ts...@ietf.org> > *Subject:* Re: [tsvwg] Re: UDP options [was IP Parcels and Advanced > Jumbos (AJs)] > > > > On Fri, Nov 15, 2024, 6:30 PM Templin (US), Fred L <Fred.L.Templin= > 40boeing....@dmarc.ietf.org> wrote: > > Tom, > > > > >Is there any interaction between GRO/GSO and IP parcels then? > > > > An IP parcel is exactly a multi-segment GSO buffer packaged for > transmission over an Internetwork. > > > > Hi Fred, > > > > Let me rephrase. Does the GRO/GSO implementation need to change because of > IP parcels? > > > > Tom > > > > Fred > > > > *From:* Tom Herbert <tom=40herbertland....@dmarc.ietf.org> > *Sent:* Friday, November 15, 2024 10:09 AM > *To:* Templin (US), Fred L <fred.l.temp...@boeing.com> > *Cc:* C. M. Heard <he...@pobox.com>; Gorry Fairhurst <go...@erg.abdn.ac.uk>; > Joe Touch <to...@strayalpha.com>; int-area <int-area@ietf.org>; 6man < > i...@ietf.org>; TSVWG <ts...@ietf.org> > *Subject:* Re: [IPv6]Re: [EXTERNAL] Re: [tsvwg] Re: UDP options [was IP > Parcels and Advanced Jumbos (AJs)] > > > > On Fri, Nov 15, 2024, 6:01 PM Templin (US), Fred L <Fred.L.Templin= > 40boeing....@dmarc.ietf.org> wrote: > > Hi Mike, > > > > This is exactly what happens with Generic Segment Offload (GSO) and > Generic Receive Offload (GRO) in real networks today. After a multi-segment > GSO buffer is broken into individual IP packets during packetization, the > receiver applies GRO to restore the multi-segment buffer if possible; > otherwise, it delivers the individual IP packets to the upper layer. Each > individual IP packet is an atomic unit that will be understood by upper > layers even if it is not restored into the original multi-segment buffer > originally prepared by GSO. This is the way GSO/GRO work today, and IP > parcels does not change that. > > > > Hi Fred, > > > > Is there any interaction between GRO/GSO and IP parcels then? > > > > Tom > > > > > > Fred > > > > *From:* C. M. Heard <he...@pobox.com> > *Sent:* Friday, November 15, 2024 9:36 AM > *To:* Templin (US), Fred L <fred.l.temp...@boeing.com> > *Cc:* Gorry Fairhurst <go...@erg.abdn.ac.uk>; Joe Touch < > to...@strayalpha.com>; int-area <int-area@ietf.org>; 6man <i...@ietf.org>; > TSVWG <ts...@ietf.org> > *Subject:* [EXTERNAL] Re: [tsvwg] Re: UDP options [was IP Parcels and > Advanced Jumbos (AJs)] > > > > EXT email: be mindful of links/attachments. > > > > > Fred, > > > > I very strongly disagree with your statement that it is not an error to > "it will instead deliver each of the individual IP packets to upper layers > without restoring the parce." > > > > That amounts to delivering PIECES of the UDP packet sent by the originator > to the upper layer. This would be exactly equivalent to allowing a receiver > that does not understand the UDP FRAG option to deliver the payload of each > individual fragment to the upper layer. The UDP options draft goes to > considerable effort to ensure that this does not happen. > > > > There is long-standing precedent that the boundaries of UDP datagrams are > preserved during transmission across the Internet. Many if not all > UDP-based protocols depend on that, explicitly or implicitly. I do not > understand why this point is even considered open for discussion. > > > > Mike > > > > On Fri, Nov 15, 2024 at 8:26 AM Templin (US), Fred L < > fred.l.temp...@boeing.com> wrote: > > Hi Mike, > > > > Thank you for looking and commenting. A UDP/IP parcel containing N > segments that undergoes packetization somewhere along the path will arrive > at the final destination as N individual IP packets, each containing a > Parcel Parameters UDP option. If the destination recognizes the option, it > will restore the N segment parcel within the kernel before delivering the > entire parcel as a single unit to upper layers. If the destination does not > recognize the option, it will instead deliver each of the individual IP > packets to upper layers without restoring the parcel which is not an error. > Very significantly, each of the individual IP packets can be dealt with as > standalone units once packetization has been applied; it is just that if > the receive-side does not apply restoration (i.e., GRO) the performance > optimization will be lost at that end. So, I don’t think there is any > problem to worry about. > > > > Fred Templin > > > > *From:* C. M. Heard <he...@pobox.com> > *Sent:* Thursday, November 14, 2024 4:55 PM > *To:* Templin (US), Fred L <fred.l.temp...@boeing.com> > *Cc:* Gorry Fairhurst <go...@erg.abdn.ac.uk>; Joe Touch < > to...@strayalpha.com>; int-area <int-area@ietf.org>; 6man <i...@ietf.org>; > TSVWG <ts...@ietf.org> > *Subject:* Re: [tsvwg] Re: UDP options [was IP Parcels and Advanced > Jumbos (AJs)] > > > > Fred and WG participants, > > > > I have finally freed up some cycles to read draft-templin-6man-parcels2-14 > <https://datatracker.ietf.org/doc/html/draft-templin-6man-parcels2-14>, > and I have found some issues with it that need to be addressed with respect > to its handling of UDP. > > > > The big one -- if I have correctly understood what I have read -- is that > it's possible for a single parcel of a parcellated UDP packet to be turned > into a stand-alone UDP packet (see Section 7.1 > <https://datatracker.ietf.org/doc/html/draft-templin-6man-parcels2#name-packetization-over-non-parc>) > and delivered to an end system as such (see Section 7.4 > <https://datatracker.ietf.org/doc/html/draft-templin-6man-parcels2#name-final-destination-restorati>). > That packet would contain a Parcel Parameters UDP Option to tell the > endpoint host that the packet is a parcel and not a complete UDP datagram, > but the option kind is taken from the SAFE option space (KIND = 127; see > draft-ietf-tsvwg-udp-options#section-10 > <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-udp-options#section-10>). > Legacy endpoints that do not understand UDP options will ignore that SAFE > option and will deliver the parcel as if it were a complete UDP datagram. > That, to my mind, is completely unacceptable. Unlike TCP, which is a > byte-stream protocol in which segment boundaries have no meaning for the > upper layer, UDP is a datagram protocol in which message boundaries are > meaningful to the upper layer. The protocol has a contract with the upper > layer to deliver a message as it was submitted or not at all. Delivering a > parcel in a manner that can be misinterpreted as a complete datagram > violates that contract. > > > > It is possible to repair this defect by making the Parcel Parameters > Option, or something with equivalent functionality, into an UNSAFE option. > My suggestion would be to define an UNSAFE version of the existing FRAG > option (see draft-ietf-tsvwg-udp-options#section-11.4 > <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-udp-options#section-11.4>) > -- let's call it UFRAG -- that would allow for packet sizes greater than > 65,535 bytes. The same option could be used to send singleton advanced > jumbo packets as atomic fragments. This would avoid any need to modify the > base UDP and UDP Options specifications. > > > > Additionally: during the review of draft-ietf-tsvwg-udp-options > <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-udp-options>, Joe > Touch correctly pointed out that RFC 2675 > <https://datatracker.ietf.org/doc/html/rfc2675> (and its predecessor RFC > 2147 <https://datatracker.ietf.org/doc/html/rfc2147>) failed to note that > it updated RFC 768 <https://datatracker.ietf.org/doc/html/rfc768>. > Similar concerns apply to TCP. If this draft foes forward, it should note > that it updates the UDP and TCP specifications, and it should get buy-in > from TSVWG and TCPM. > > > > Thanks and regards, > > > > Mike Heard > > > > > > > > > > > > On Sun, Sep 29, 2024 at 3:51 PM C. M. Heard <he...@pobox.com> wrote: > > Fred, > > > > I currently hold the editing pen for the changes to the UDP Options draft > that have been requested prior to the shepherd report, and my intention is > to remain silent about how, if at all, IP Parcels and Advanced Jumbos (AJs) > will support UDP Options. > > > > I'll provide comments on the IP Parcels and Advanced Jumbos work at a > later date, when I have spare intellectual cycles to fully comprehend the > contents of draft-templin-6man-parcels2. At this point I must confess that, > like Brian, I do not understand how a receiver will locate the options > trailer in the case of an IP Payload Length exceeding 65535. Like Joe, I > think it would be better to put the options just after the UDP header and > make a new UNSAFE option to delimit the position where the options end and > the user data begins.. But that discussion (and the corresponding update to > the UDP options draft) can occur when it is ripe; IMO that is not the case > at this time. > > > > Respectfully, > > > > Mike Heard > > > > On Sun, Sep 29, 2024 at 3:07 PM Templin (US), Fred L <Fred.L.Templin= > 40boeing....@dmarc.ietf.org> wrote: > > IP parcels and Advanced Jumbos (AJs) of all sizes ranging from 1 to 2^32 > are now eligible > > for using UDP options. This is just one way in which they offer a better > service than RFC2675 > > Jumbograms, but there are also many others. > > > > Joe, you can either note this in your draft or just leave it be and let my > draft do an > > “updates UDP options”. > > > > Thank you - Fred > > > > *From:* Brian Carpenter <brian.e.carpen...@gmail.com> > *Sent:* Saturday, September 28, 2024 2:20 AM > *To:* Gorry (erg) <go...@erg.abdn.ac.uk> > *Cc:* Joe Touch <to...@strayalpha.com>; Templin (US), Fred L < > fred.l.temp...@boeing.com>; Tim Chown <tim.ch...@jisc.ac.uk>; Internet > Area <Int-area@ietf.org>; IPv6 List <i...@ietf.org>; tsvwg IETF list < > ts...@ietf.org> > *Subject:* [EXTERNAL] Re: [tsvwg] Re: UDP options [was IP Parcels and > Advanced Jumbos (AJs)] > > > > EXT email: be mindful of links/attachments. > > > > > That works for me.. > > > > (via tiny screen & keyboard) > Regards, > Brian Carpenter > > > > On Sat, 28 Sept 2024, 19:08 Gorry (erg), <go...@erg.abdn.ac.uk> wrote: > > See below > > > On 28 Sep 2024, at 04:05, Brian E Carpenter <brian.e.carpen...@gmail.com> > wrote: > > > > Joe, > > On 28-Sep-24 03:13, to...@strayalpha.com wrote: > >>>> On Sep 27, 2024, at 7:58 AM, Templin (US), Fred L <Fred.L.Templin= > 40boeing....@dmarc.ietf.org> wrote: > >>> > >>>> Indeed. But if sendmsg() and recvmsg() can and do generate RFC2675 > packets, it means that any discussion of obsoleting RFC2675 should be > >>>> off the table. > >>> > >>> No one that I know of has suggested obsoleting RFC2675 - my documents > do not say "obsoletes" (nor even "updates”). > >> That approach to UDP jumbo grams is incompatible with UDP options. > >> And yes, there was a proposal to move that RFC to historic: > >> Jones, T., G. Fairhurst, "Change Status of RFC 2675 to Historic," > draft-jones-6man-historic-rfc2675, May 2019. > >> We COULD have a new option with a longer length, but that’s not in our > baseline draft. > > > > Wouldn't that be tricky, because the options follow the whole payload as > I understand it? So a JumboUDPgram has to be received in full, however big > it is, before the option saying that it's a jumbo can be received and > interpreted. > > > > Where the udp-options draft says: > > > >>> The technique has been proposed for deprecation [Jo19]. > > > > I think you'd better change it to something like: > > > > The technique is known to be in active use in special situations, so > cannot reasonably be deprecated. However, users of this technique cannot > simultaneously use UDP options. > > > > Brian > > > I do not think the I-D needs to say anything about the deployment status > of jumbograms, that another topic. > > I suggest if people wish, we just say that users of this technique can or > cannot simultaneously use UDP options. > > Gorry > > > > > > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > i...@ietf.org > List Info: https://mailman3.ietf.org/mailman3/lists/i...@ietf.org/ > -------------------------------------------------------------------- > >
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