Re: [Int-area] [EXTERNAL] Re: A new link service model for the Internet (IP Parcels and Advanced Jumbos)

[Tom Herbert <[e-mail]>]

On Tue, Nov 14, 2023 at 10:36 AM Templin (US), Fred L
<[e-mail]> wrote:
>
> Tom, for IP parcels and advanced jumbos, the {TCP, UDP} checksums cover only the pseudo-header
> of the IP header followed by the fields of the {TCP, UDP} header itself; the checksum does not extend
> to cover the parcel/jumbo body. In this way, it is very much like the IPv4 header checksum and covers
> only header fields and no data octets. The reason for this is that the IP parcel and advanced jumbo
> data segments each have their own CRCs for integrity verification.

Fred,

So this is a type of new checksum of L4 checksum, not the TCP/UDP
checksum defined in RFC793/RFC768? Do you really need this checksum to
cover the transport layer header, could it just be over pseudo header?
(that would greatly simplify router operations)

Tom


>
> Fred
>
> > -----Original Message-----
> > From: Tom Herbert <[e-mail]>
> > Sent: Tuesday, November 14, 2023 10:02 AM
> > To: Templin (US), Fred L <Fred.L.Templin=[e-mail]>
> > Cc: Templin (US), Fred L <[e-mail]>; Joel Halpern <[e-mail]>; int-area <[e-mail]>
> > Subject: Re: [Int-area] [EXTERNAL] Re: A new link service model for the Internet (IP Parcels and Advanced Jumbos)
> >
> > EXT email: be mindful of links/attachments.
> >
> >
> >
> > On Tue, Nov 14, 2023 at 8:11 AM Templin (US), Fred L
> > <Fred.L.Templin=[e-mail]> wrote:
> > >
> > > Tom, thinking more about this IPv6 does not verify header checksums at every hop – only at the
> > >
> > > final destination. So, how would it be if we simply made header checksum verification a SHOULD
> > >
> > > at intermediate hops but a MUST at the final destination?
> >
> > Fred,
> >
> > So if I understand correctly, this would be validating the TCP and UDP
> > checksum at intermediate hops? Frankly, that's going to be a hard sell
> > to router vendors, they don't generally have the capability to compute
> > those checksums. Also, it's not guaranteed that a TCP and UDP checksum
> > are guaranteed to be maintained to be correct while the packet is
> > inflight. I believe in current specifications this For instance,
> > draft-mizrahi-spring-l4-checksum-srv6-00 would potentially make
> > checksums incorrect while packets are inflight.
> >
> > Tom
> >
> > >
> > >
> > >
> > >
> > >
> > > Thanks - Fred
> > >
> > >
> > >
> > > From: Int-area <[e-mail]> On Behalf Of Templin (US), Fred L
> > > Sent: Tuesday, November 14, 2023 7:28 AM
> > > To: Tom Herbert <tom=[e-mail]>
> > > Cc: Joel Halpern <[e-mail]>; int-area <[e-mail]>
> > > Subject: Re: [Int-area] [EXTERNAL] Re: A new link service model for the Internet (IP Parcels and Advanced Jumbos)
> > >
> > >
> > >
> > > Tom, the IP parcel / advanced jumbo header checksum is on the same order of complexity as the
> > >
> > > IPv4 header checksum and covers a similar amount of header data – the checksum does not run
> > >
> > > over the entire length of the parcel/jumbo. Routers that accept IP parcels and advanced jumbos
> > >
> > > would need to verify the IP addresses and {TCP,UDP} port numbers if they receive a parcel that
> > >
> > > was flagged as a CRC error by lower layers – that is all.
> > >
> > >
> > >
> > > Thanks - Fred
> > >
> > >
> > >
> > > From: Tom Herbert <tom=[e-mail]>
> > > Sent: Monday, November 13, 2023 3:38 PM
> > > To: Templin (US), Fred L <[e-mail]>
> > > Cc: Joel Halpern <[e-mail]>; int-area <[e-mail]>
> > > Subject: Re: [Int-area] [EXTERNAL] Re: A new link service model for the Internet (IP Parcels and Advanced Jumbos)
> > >
> > >
> > >
> > > EXT email: be mindful of links/attachments.
> > >
> > >
> > >
> > >
> > >
> > >
> > > On Mon, Nov 13, 2023, 6:01 PM Templin (US), Fred L <Fred.L.Templin=[e-mail]> wrote:
> > >
> > > Joel, I am asking this only for IP parcels and advanced jumbos over links that support them natively.
> > > When a router with a link that supports IP parcels and advanced jumbos natively receives an
> > > ethernet frame with bad CRC, it first checks to see if it is an IP parcel/advanced jumbo. If so, the
> > > router performs an integrity check on the {TCP,UDP}/IP headers and discards the frame if the
> > > header checksum is incorrect. Only if the {TCP,UD}/IP header checksum is correct does the
> > > router forward the (errored) frame. This procedure is repeated at every IP forwarding hop
> > > along the parcel/jumbo-capable path to the final destination.
> > >
> > >
> > >
> > > Fred,
> > >
> > >
> > >
> > > This would mean that routers would not only have process L4 headers in flight which is already an architectural abomination they often
> > do, they'd also have to compute header checksums on L4. It's unlikely router vendors are going to be excited to do that. IMO, it would be
> > better to avoid having routers dabble in L4 at all for this.
> > >
> > >
> > >
> > > Tom
> > >
> > >
> > >
> > >
> > > Fred
> > >
> > > > -----Original Message-----
> > > > From: Joel Halpern <[e-mail]>
> > > > Sent: Monday, November 13, 2023 2:53 PM
> > > > To: Templin (US), Fred L <[e-mail]>
> > > > Cc: [e-mail]
> > > > Subject: [EXTERNAL] Re: [Int-area] A new link service model for the Internet (IP Parcels and Advanced Jumbos)
> > > >
> > > > EXT email: be mindful of links/attachments.
> > > >
> > > >
> > > >
> > > > You seem to be asking that every router in the Internet deliver frames
> > > > with bad Ethernet CRCs.(which may have bad destination addresses, since
> > > > routers do not check upper layer checksums)  This is asking every router
> > > > and eveyr link to pay a significant in the hope that sometimes someone
> > > > may be able to safely reconstruct the frame.
> > > >
> > > > Or are you proposing this for some other network that is not IETF business?
> > > >
> > > > Yours,
> > > >
> > > > Joel
> > > >
> > > > On 11/13/2023 5:43 PM, Templin (US), Fred L wrote:
> > > > > Joel, I don't mind leaving the IEEE specs alone and allowing the receiver to deliver errored
> > > > > frames to upper layers along with a CRC error flag. The CRC error flag would also make for
> > > > > a good indication to the IP layer of when the IP addresses and port numbers should be
> > > > > checked for consistency so there is value in continuing to let the CRC do its work.
> > > > >
> > > > > About delay and disruption tolerance, IP parcels and advanced jumbos present a ready-made
> > > > > vehicle for supporting performance maximization, carrying FEC data, etc. And, this will be
> > > > > important for more than just space systems with their long delay links - it will become more
> > > > > and more important for all air/land/sea/space mobility scenarios as the Internet becomes
> > > > > more and more mobile and more and more interplanetary. I think that should already be
> > > > > of interest to Intarea.
> > > > >
> > > > > Fred
> > > > >
> > > > >> -----Original Message-----
> > > > >> From: Joel Halpern <[e-mail]>
> > > > >> Sent: Monday, November 13, 2023 1:59 PM
> > > > >> To: Templin (US), Fred L <[e-mail]>
> > > > >> Cc: [e-mail]
> > > > >> Subject: [EXTERNAL] Re: [Int-area] A new link service model for the Internet (IP Parcels and Advanced Jumbos)
> > > > >>
> > > > >> EXT email: be mindful of links/attachments.
> > > > >>
> > > > >>
> > > > >>
> > > > >> Top posting two small but important points to Fred:
> > > > >>
> > > > >> 1) Changing Ethernet CRC behavior is up to IEEE.  IETF is not free to
> > > > >> redefine that.
> > > > >>
> > > > >> 2) There are approaches for links with long delays (sometimes even
> > > > >> longer than the 8 minutes to which you refer).  If you want to propose
> > > > >> different mechanisms, have the discussion with the delay tolerant
> > > > >> networking working group.  It would be rather odd to change IPv6 for
> > > > >> that case, and even odder to do without their making a request for a change.
> > > > >>
> > > > >> Yours,
> > > > >>
> > > > >> Joel
> > > > >>
> > > > >> On 11/13/2023 4:40 PM, Templin (US), Fred L wrote:
> > > > >>> Hi Tom,
> > > > >>>
> > > > >>> On Mon, Nov 13, 2023 at 1:11 PM Templin (US), Fred L
> > > > >>> <Fred.L.Templin=[e-mail]> wrote:
> > > > >>>> Hi Tom, see below for responses:
> > > > >>>>
> > > > >>>>> -----Original Message-----
> > > > >>>>> From: Int-area <[e-mail]> On Behalf Of Tom Herbert
> > > > >>>>> Sent: Monday, November 13, 2023 12:39 PM
> > > > >>>>> To: Templin (US), Fred L <Fred.L.Templin=[e-mail]>
> > > > >>>>> Cc: [e-mail]
> > > > >>>>> Subject: [EXTERNAL] Re: [Int-area] A new link service model for the Internet (IP Parcels and Advanced Jumbos)
> > > > >>>>>
> > > > >>>>> EXT email: be mindful of links/attachments.
> > > > >>>>>
> > > > >>>>>
> > > > >>>>>
> > > > >>>>> On Mon, Nov 13, 2023 at 11:58 AM Templin (US), Fred L
> > > > >>>>> <Fred.L.Templin=[e-mail]> wrote:
> > > > >>>>>> Here is something everyone should read and become familiar with taken from Section 5 of the latest
> > > > >>>>>> version of "IP Parcels and Advanced Jumbos":
> > > > >>>>>>
> > > > >>>>>> https://datatracker.ietf.org/doc/draft-templin-intarea-parcels/
> > > > >>>>>>
> > > > >>>>>> A new link service model is offered that will be essential for supporting air/land/sea/space mobile
> > > > >>>>>> Internetworking. IP Parcels and Advanced Jumbos are the vehicles that support end-to-end as
> > > > >>>>>> opposed to hop-by-hop link error detection in the new model.
> > > > >>>>>>
> > > > >>>>>> This is a truly transformational concept for the Internet - many may already know about it, but
> > > > >>>>>> everyone should become aware of it.
> > > > >>>>> Hi Fred,
> > > > >>>>>
> > > > >>>>> Some comments in line.
> > > > >>>>>
> > > > >>>>>> Fred
> > > > >>>>>> ---
> > > > >>>>>> 5.  IP Parcel and Advanced Jumbo Link Service Model
> > > > >>>>>>
> > > > >>>>>>      The classical Internetworking link service model requires each link
> > > > >>>>>>      in the path to apply a link-layer packet integrity check often termed
> > > > >>>>>>      a "Cyclic Redundancy Check (CRC)".  The link near-end calculates and
> > > > >>>>>>      appends a CRC code value (often 4 octets) to each packet pending
> > > > >>>>>>      transmission, and the link far-end verifies the CRC upon packet
> > > > >>>>>>      receipt.  If the CRC is incorrect, the link far-end unconditionally
> > > > >>>>>>      discards the packet.  This process is repeated for each link in the
> > > > >>>>>>      path so that only packets that pass all link-layer CRC checks are
> > > > >>>>>>      delivered to the final destination.
> > > > >>>>>>
> > > > >>>>>>      While this link service model has contributed to the unparalleled
> > > > >>>>>>      success of terrestrial Internetworks (including the global public
> > > > >>>>>>      Internet), new uses in which significant delays or disruptions can
> > > > >>>>>>      occur are not as well supported.  For example, a path that contains
> > > > >>>>>>      links with significant bit errors may be challenged to pass a
> > > > >>>>>>      majority percentage of packets since loss due to CRC failures can
> > > > >>>>>>      occur at any hop while each packet lost must be retransmitted.  With
> > > > >>>>>>      the advent of space-domain Internetworking, the long delays
> > > > >>>>>>      associated with interplanetary signal propagation can also often
> > > > >>>>>>      render any retransmissions useless especially when communications
> > > > >>>>>>      latency is critical.
> > > > >>>>> How would this compare to an L2 reliable protocol that is able to
> > > > >>>>> retransmit over links in the path that are particularly lossy? If
> > > > >>>>> latency is critical then we probably can't do any better than
> > > > >>>>> retransmitting at L2.
> > > > >>>> Link-layer retransmissions are still beneficial on low-delay links yes. But, if
> > > > >>>> slightly errored data is still received after N tries, the errored data should be
> > > > >>>> forwarded to the next hop toward the final destination instead of simply
> > > > >>>> dropped. Link-layer retransmissions on long-delay links (like 4min OWLT
> > > > >>>> from earth to mars) might not be as beneficial.
> > > > >>>>
> > > > >>>>>>      IP parcels and advanced jumbos now offer a new link service model;
> > > > >>>>>>      instead of requiring an independent CRC at each intermediate link
> > > > >>>>>>      hop, IP parcels and advanced jumbos include a CRC code with each
> > > > >>>>>>      segment that is calculated and inserted by the original source and
> > > > >>>>>>      verified by the final destination.
> > > > >>>>> So basically this is an end to end CRC and we'd have to disable the L2
> > > > >>>>> CRC, like Ethernet CRC, everywhere along the path for it to work?
> > > > >>>> It would still work with Ethernet CRC enabled along the path, but the Ethernet
> > > > >>>> CRCs would be redundant with the parcel/advanced jumbo segment CRCs. It
> > > > >>>> might be OK to leave Ethernet CRCs in place, but have the link far end forward
> > > > >>>> any packets with link errors instead of dropping - but, then the Ethernet CRC
> > > > >>>> operations would essentially be wasted energy so better to disable them.
> > > > >>>>
> > > > >>>>>>      Each intermediate hop must
> > > > >>>>>>      therefore pass IP parcels and advanced jumbos without applying
> > > > >>>>>>      traditional link layer CRC checks and/or discarding packets that
> > > > >>>>>>      contain errors.  This relaxes the burden on intermediate systems and
> > > > >>>>>>      delivers all data that transits the path to the destination end
> > > > >>>>>>      system which is uniquely positioned to coordinate recovery of any
> > > > >>>>>>      data that was either lost or corrupted in transit.
> > > > >>>>> "Burden on intermediate" systems is relative. If this refers to
> > > > >>>>> Ethernet routers then the burden of CRC has long been assumed. It will
> > > > >>>>> be more trouble to undo that. Getting the bad packets to the transport
> > > > >>>>> layer might be helpful, assuming that the packet isn't corrupted so
> > > > >>>>> much that the receiver can identify the flow. I would point out that
> > > > >>>>> if the addresses of the packet and probably some other fields are
> > > > >>>>> corrupted and the packet isn't not dropped by the network then this
> > > > >>>>> increases the chances of packet misdelivery-- there may be some
> > > > >>>>> security ramifications there.
> > > > >>>> Right, I should have said that there is still hop-by-hop integrity checking done
> > > > >>>> on the IP parcel and advanced jumbo headers (including addresses and port
> > > > >>>> numbers) to avoid mis-delivery as you say. But, that is with an Internet layer
> > > > >>>> checksum and not an L2 CRC.
> > > > >>>>
> > > > >>>>>>      Each IP parcel and/or advanced jumbo-capable hop along the path from
> > > > >>>>>>      the original source to the final destination must therefore provide
> > > > >>>>>>      an API primitive to inform the link ingress to disable link-layer
> > > > >>>>>>      integrity checks for the current IP parcel or advanced jumbo payload.
> > > > >>>>>>      The parcel/advanced jumbo may therefore collect cumulative link
> > > > >>>>>>      errors along the path, but these will be detected by the per segment
> > > > >>>>>>      CRC checks performed by the final destination.  The final destination
> > > > >>>>>>      in turn delivers each segment to the local transport layer along with
> > > > >>>>>>      a "CRC error" flag that is set if a CRC error was detected or clear
> > > > >>>>>>      otherwise.  The CRC indication is then taken under advisement by the
> > > > >>>>>>      transport layer, which should consult any transport or higher-layer
> > > > >>>>>>      integrity checks to pursue corrective actions.
> > > > >>>>>>
> > > > >>>>>>      IP parcels and advanced jumbos therefore provide a revolutionary
> > > > >>>>>>      advancement for delay/disruption tolerance in air/land/sea/space
> > > > >>>>>>      mobile Internetworking applications.  As the Internet continues to
> > > > >>>>>>      evolve from its more stable fixed terrestrial network origins to one
> > > > >>>>>>      where more and more nodes operate in the mobile edge, this new link
> > > > >>>>>>      service model relocates error detection and correction
> > > > >>>>>>      responsibilities from intermediate systems to the end systems that
> > > > >>>>>>      are best positioned to take corrective actions.
> > > > >>>>>>
> > > > >>>>>>      Note: To be verified, IP parcels and advanced jumbos may be realized
> > > > >>>>>>      through simple software updates for widely-deployed link types such
> > > > >>>>>>      as 1/10/100-Gbps Ethernet.  If the network driver API provides a
> > > > >>>>>>      primitive allowing the IP layer to disable link layer integrity
> > > > >>>>>>      checks on a per-"packet" basis, even very large IP parcels and
> > > > >>>>>>      advanced jumbos should be capable of transiting the link since
> > > > >>>>>>      Ethernet link transmission unit sizes are bounded by software and not
> > > > >>>>>>      hardware constraints.
> > > > >>>>> I don't believe disabling the Ethernet CRC is feasible. AFAIK IEEE
> > > > >>>>> 802.3 standards don't allow the Ethernet CRC to be optional. Even if
> > > > >>>>> it were, I doubt any existing NIC hardware or router hardware would
> > > > >>>>> have an API to disable CRC.
> > > > >>>>> That may well be true for current-day hardware, but I can easily imagine future
> > > > >>>>> hardware that presents such an API - or, maybe we need to define a new
> > > > >>>>> EtherType for which the future hardware omits the CRC checks.
> > > > >>>> Fred,
> > > > >>>>
> > > > >>>> A new EtherType wouldn't help. The CRC is an integral part of the
> > > > >>>> Ethernet frame. To make it optional would probably require standards
> > > > >>>> action in IEEE (or appropriate SDO for other L2 technologies).
> > > > >>> OK, then what about set the Ethernet CRC to 0 on transmit and ignore on receipt?
> > > > >>> Which is a behavior that could be keyed off of EtherType.
> > > > >>>
> > > > >>>>> By the way, this is the only way feasible I see for making Internet-like protocols work
> > > > >>>>> over long-delay space-domain links or mobile network edge links that are subject to
> > > > >>>>> significant disruption. Better to deliver (slightly) errored data to the final destination
> > > > >>>>> instead of no data, especially when retransmission delays are intolerable. The final
> > > > >>>>> destination will find a way to make sense out of as much of the received data as
> > > > >>>>> possible, which is way better than nothing.
> > > > >>>> Well, it's not like we are starting from nothing. For instance, TCP
> > > > >>>> selective ACKs allow a receiver to basically tell the sender what
> > > > >>>> segments were received (and implicitly what segments were dropped) and
> > > > >>>> need to be retransmitted. This doesn't work if the drops are at the
> > > > >>>> tail of a communication, and in that case it might be useful to send
> > > > >>>> some sort of selective NAK back to the sender which I imagine is what
> > > > >>>> your proposal might facilitate.
> > > > >>> TCP selective ACK is not helpful over links with 8 minute round-trip times. Also
> > > > >>> probably not great over links with high BERs. Better to get as much data through
> > > > >>> to the destination as possible in the first try whether/not it has errors and let the
> > > > >>> destination either accept it as-is or repair it if it is able to. Forward error correction
> > > > >>> at the destination should be helpful - retransmission requests should be a low
> > > > >>> preference last resort.
> > > > >>>
> > > > >>> Thank you - Fred
> > > > >>>
> > > > >>>> Tom
> > > > >>>>
> > > > >>>>> Thank you - Fred
> > > > >>>>>
> > > > >>>>>> Tom
> > > > >>>>>>> _______________________________________________
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