Tom, > SR aware routers to update L4 checksum
That is completely unrealistic. Show me the box which can forward all interfaces at 800 Gb/s and read entire each packet and compute upper layer checksum on it. If anything just do encap and move on. Thx, R. On Thu, Apr 4, 2024 at 7:06 PM Tom Herbert <t...@herbertland.com> wrote: > > > On Thu, Apr 4, 2024, 12:30 PM Robert Raszuk <rob...@raszuk.net> wrote: > >> Hi Tom, >> >> Yes I am with you here. >> >> However let's observe that this is pretty common best practice to disable >> any hardware offload on the box when running tcpdump or wireshark. >> >> In fact some implementations (F5) do it for you automagically :) >> >> And as it has been said based on the fact that hardware offload does not >> understand any Routing Headers it really does not matter if it is there or >> not :) >> > > Robert, > > tcpdump is independent of hardware offload. If the checksum is incorrect > per the packet contents we'll see bad checksums reported if we snoop > packets, but like I said, we can't differentiate the bad from the good. > > Offload becomes an issue for NICs that do protocol specific checksum > offload. We lose the capability on RX which is an inconvenience, on TX we'd > need to change the implementation to ensure the checksum is not computed by > HW. > > If SR without SRH is needed, then I believe the best answer is for SR > aware routers to update L4 checksum when they change DA per NAT > requirements. This solves tcpdump as well as offloads. > > Tom > > >> Cheers, >> R. >> >> >> On Thu, Apr 4, 2024 at 6:11 PM Tom Herbert <tom= >> 40herbertland....@dmarc.ietf.org> wrote: >> >>> >>> >>> On Thu, Apr 4, 2024, 11:48 AM Francois Clad <fclad.i...@gmail.com> >>> wrote: >>> >>>> Hi Tom, >>>> >>>> Tcpdump can determine that this packet is steered onto an SRv6 path by >>>> checking if the DA matches the SRv6 SID block. >>>> >>> >>> Francois, >>> >>> That would require introducing external state to tcpdump for correct >>> operation. This would be a major divergence in both implementation and ops >>> compared to how things work today. >>> >>> Tom >>> >>> >>> >>>> Thanks, >>>> Francois >>>> >>>> On 4 Apr 2024 at 16:59:59, Tom Herbert <t...@herbertland.com> wrote: >>>> >>>>> >>>>> >>>>> On Thu, Apr 4, 2024, 9:39 AM Francois Clad <fclad.i...@gmail.com> >>>>> wrote: >>>>> >>>>>> Hi Mark, >>>>>> >>>>>> Tcpdump/wireshark decodes the IPv6 header just fine. I do not see any >>>>>> issue here. >>>>>> >>>>> >>>>> Francois, >>>>> >>>>> The problem is that tcpdump can't tell that a packet is an SR packet >>>>> if there's no SRH. For instance, if the checksum is not maintained to be >>>>> correct in the wire then tcpdump will show that the packet has a bad L4 >>>>> checksum, but there's no way to tell if that is an SR packet or if the >>>>> checksum is actually bad. This will make debugging checksum failures in >>>>> the >>>>> network much more difficult, and this affects our ability to debug all >>>>> traffic not just SR packets. >>>>> >>>>> Tom >>>>> >>>>> >>>>>> Cheers, >>>>>> Francois >>>>>> >>>>>> On 4 Apr 2024 at 14:09:43, Mark Smith <markzzzsm...@gmail.com> wrote: >>>>>> >>>>>>> >>>>>>> >>>>>>> On Thu, 4 Apr 2024, 22:50 Francois Clad, <fclad.i...@gmail.com> >>>>>>> wrote: >>>>>>> >>>>>>>> Hi Alvaro, all, >>>>>>>> >>>>>>>> RFC 8754 allows the SR source node to omit the SRH when it contains >>>>>>>> redundant information with what is already carried in the base IPv6 >>>>>>>> header. >>>>>>>> Mandating its presence for C-SID does not resolve any problem because >>>>>>>> it >>>>>>>> will not provide any extra information to the nodes along the packet >>>>>>>> path. >>>>>>>> >>>>>>> >>>>>>> How are troubleshooting tools like 'tcpdump' going to know how to >>>>>>> automatically decode these packets as SRv6 packets if there is no SRH? >>>>>>> >>>>>>> >>>>>>> >>>>>>>> Specifically for the case of middleboxes attempting to verify the >>>>>>>> upper-layer checksum, >>>>>>>> >>>>>>>> - An SRv6-unaware middlebox will not be able to verify the >>>>>>>> upper-layer checksum of SRv6 packets in flight, regardless of >>>>>>>> whether an >>>>>>>> SRH is present or not. >>>>>>>> - An SRv6 and C-SID aware middlebox will be able to find the >>>>>>>> ultimate DA and verify the upper-layer checksum in flight, >>>>>>>> regardless of >>>>>>>> whether an SRH is present or not. >>>>>>>> >>>>>>>> >>>>>>>> Furthermore, transit nodes (e.g., middleboxes) should not attempt >>>>>>>> to identify SRv6 traffic based on the presence of the SRH, because they >>>>>>>> will miss a significant portion of it: all the best-effort or Flex-Algo >>>>>>>> traffic steered with a single segment may not include an SRH, even >>>>>>>> without >>>>>>>> C-SID. Instead, RFC 8402, 8754, and 8986 define identification rules >>>>>>>> based >>>>>>>> on the SRv6 SID block. >>>>>>>> >>>>>>>> Thanks, >>>>>>>> Francois >>>>>>>> >>>>>>>> >>>>>>>> On 2 Apr 2024 at 19:44:51, Alvaro Retana <aretana.i...@gmail.com> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> [Moving this conversation up on your mailbox. :-) ] >>>>>>>>> >>>>>>>>> [Thanks, Robert and Tom for your input!] >>>>>>>>> >>>>>>>>> >>>>>>>>> We want to hear from more of you, including the authors. Even if >>>>>>>>> you already expressed your opinion in a different thread, please >>>>>>>>> chime in >>>>>>>>> here. >>>>>>>>> >>>>>>>>> We will collect feedback until the end of this week. >>>>>>>>> >>>>>>>>> Thanks! >>>>>>>>> >>>>>>>>> Alvaro. >>>>>>>>> >>>>>>>>> On March 28, 2024 at 8:06:18 AM, Alvaro Retana ( >>>>>>>>> aretana.i...@gmail.com) wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>> Focusing on the C-SID draft, some have suggested requiring the >>>>>>>>> presence of the SRH whenever C-SIDs are used. Please discuss whether >>>>>>>>> that >>>>>>>>> is the desired behavior (or not) -- please be specific when debating >>>>>>>>> the >>>>>>>>> benefits or consequences of either behavior. >>>>>>>>> >>>>>>>>> Please keep the related (but independent) discussion of requiring >>>>>>>>> the SRH whenever SRv6 is used separate. This larger topic may impact >>>>>>>>> several documents and is better handled in a different thread (with >>>>>>>>> 6man >>>>>>>>> and spring included). >>>>>>>>> >>>>>>>>> Thanks! >>>>>>>>> >>>>>>>>> Alvaro >>>>>>>>> -- for spring-chairs >>>>>>>>> >>>>>>>>> >>>>>>>>> -------------------------------------------------------------------- >>>>>>>>> IETF IPv6 working group mailing list >>>>>>>>> i...@ietf.org >>>>>>>>> Administrative Requests: >>>>>>>>> https://www.ietf.org/mailman/listinfo/ipv6 >>>>>>>>> >>>>>>>>> -------------------------------------------------------------------- >>>>>>>>> >>>>>>>> -------------------------------------------------------------------- >>>>>>>> IETF IPv6 working group mailing list >>>>>>>> i...@ietf.org >>>>>>>> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 >>>>>>>> -------------------------------------------------------------------- >>>>>>>> >>>>>>> -------------------------------------------------------------------- >>>>>> IETF IPv6 working group mailing list >>>>>> i...@ietf.org >>>>>> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 >>>>>> -------------------------------------------------------------------- >>>>>> >>>>> -------------------------------------------------------------------- >>> IETF IPv6 working group mailing list >>> i...@ietf.org >>> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 >>> -------------------------------------------------------------------- >>> >>
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