Show me Broadcom's SDK which does this in DNX family and we can talk more about such option.
Best, R. On Thu, Apr 4, 2024 at 9:22 PM Tom Herbert <t...@herbertland.com> wrote: > > > On Thu, Apr 4, 2024, 3:12 PM Robert Raszuk <rob...@raszuk.net> wrote: > >> 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. >> > > Robert, > > It's not necessary to calculate the whole checksum, only the L4 checksum > needs to be updated by adding in the delta checksum. With IPv6 we can also > do a checksum neutral mapping. Basically, this uses the low order 16 bits > in the DA address as the checksum adjustment value. For instance, if we can > use the low order bits in a SID block then that would be simplest to > implement. > > Tom > > >> 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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