Re: [spring] Beyond SRv6.

[Tom Herbert <[e-mail]>]

On Wed, Sep 11, 2019 at 10:20 PM Xiejingrong <[e-mail]> wrote:
>
> +1
>
> I think the need to ‘walk through the EH chain’ in fast-path is difficult, for the last 2 decades, and will for the near future I guess.
>
> The SRv6 is very careful not to ‘walk through the EH chain’.
>
> Instead it just ‘handle the least leading header(s)’, with a preceding ‘FIB lookup’ indication, and ‘FIB lookup’ is a step that will need to do in chip anyway for any packet.
>
Jingrong,

You seem to be ignoring the fact that SRH includes its own TLV
mechanism. There is no reason to believe that TLVs in the segment
header can somehow be more efficiently processed than TLVs in
Destination Options or Hop-by-Hop Options. Considering that there
seems to be almost no implementation of segment routing TLVs (so far
only Linux is reported to support it and even then the implementation
is not conformant), I'm dubious of any claims that SRv6 is chip
friendly or works in fast-path. If the idea is that TLVs in SRH really
aren't needed and will never actually be used, then it would appear
that the considerable effort in 6man WG trying to fix them was wasted
on a mere academic exercise.

Tom

> This makes SRv6 deployable in chips for the first time of EH invention by ISO and later by IPv6.
>
> This makes SRv6 the paradigm of handling any EH in chips In my opinion.
>
>
>
> One can check my understand on page 11 to 14 of the slides I prepared in ietf105 (though got no time slot to present):
>
> https://datatracker.ietf.org/meeting/105/materials/slides-105-bier-bier-ipv6-encapsulation-00.pdf
>
>
>
> DOH has it benefits, and is recommended in 8200, but the mix of many different EHs and different Option TLVs for a solution is obviously complex in data-plane.
>
> Using a single EH to the best, with the appropriate preceding indication, is simple, ordered, friendly to chip, direct, perfect.
>
> https://mailarchive.ietf.org/arch/msg/ipv6/SgkSGtSBmB4G51ajnBp3UbjJl8I
>
>
>
> Thanks
>
> Jingrong
>
>
>
> From: spring [mailto:[e-mail]] On Behalf Of Bernier, Daniel
> Sent: Thursday, September 12, 2019 11:41 AM
> To: [e-mail]; List <[e-mail]>
> Cc: Rob Shakir <[e-mail]>; 6man <[e-mail]>; Tarek Saad <[e-mail]>; Robert Raszuk <[e-mail]>
> Subject: Re: [spring] Beyond SRv6.
>
>
>
> +1
>
>
>
> The ability of using a single SRH to convey behaviour information wether they are per-segment or per-path has proven to be very simple and quick to define in various data plane targets.
>
>
>
> At first analysis, trying to replicate with CRH + DOH variants, the logic required for service programs is more complex.
>
>
>
> What happens if I need TLVs mid-point in a path but not at its end (e.g. referring to the Ole's ACME analogy) ? Would they now be defined in a seg-end-opt or a vpn-dest-opt ? If seg-end-opt then it means non-interested midpoint devices will have to lookup beyond the TLVs to get to CRH for next segment ?
>
>
>
> Similar question would be on how would we implement proxy behaviours either dynamic or static ? If I read https://tools.ietf.org/html/draft-bonica-6man-seg-end-opt-04 correctly, we then need NSH for richer service chains constructs (think Gi-LAN). This means I need CRH, some variants of DOH + NSH.
>
>
>
> I fail to see the simplicity there.
>
>
>
> Dan B
>
> ________________________________
>
> From: spring <[e-mail]> on behalf of [e-mail] <[e-mail]>
> Sent: Wednesday, September 11, 2019 8:57 PM
> To: List
> Cc: Rob Shakir; 6man; Tarek Saad; Robert Raszuk
> Subject: [EXT]Re: [spring] Beyond SRv6.
>
>
>
>
>
> Hi, folks,
>
> Last year China Telecom begun to implement SRv6 trial in Sichun province for the bearing and interconnection of video platforms which are  located in different cities, service agilities,secure sepertion, traffic steering and other features of SRv6 have been demonstrated in this trial. Based on this, SRv6 will be implementated in larger-scale in CT.
>
> No technologies is 100% perfect,I agree that compression mechanism is needed to reduce the the overhead of long SID in the long term, but it is better to be compatible withe SRH, instead of designing a complete new one. CRH is a complete new design, it move the complexities from SRH to DOH.
>
> Moreover, I hope more efforts of SRv6 should be given on how to support new services,for instance, Application-aware network (APN). Meanwhile, we should consider more on how to implmement smooth transition and protect the network assetof carriers.
>
>
>
> Best regards
>
> Chongfeng
>
>
>
>
>
> From: Dirk Steinberg
>
> Date: 2019-09-09 21:31
>
> To: Gyan Mishra
>
> CC: SPRING WG List; [e-mail]; Robert Raszuk; Rob Shakir; Tarek Saad
>
> Subject: Re: [spring] Beyond SRv6.
>
> There seems to be some confusion regarding TI-LFA.
>
> A couple of comments:
>
>
>
> - Remote LFA tunnel is not used with SR, only TI-LFA which
>
>   only operates on the node that is the PLR (point of local repair).
>
>
>
> - Any encapsulation on the ingress PE with or without EH has nothing
>
>   to do with TI-LFA except for the special case where the ingress PE
>
>   itself is the PLR.
>
>
>
> - TI-LFA is not an IGP extension and does not require one.
>
>   It is a purely local computation based on IGP topology.
>
>
>
> - The PLR for TI-LFA may need to insert some SIDs into the SID
>
>   list to steer the packet around the failure. For the LFA base case
>
>   no SIDs are needed at all. If SID insertion is needed, the PLR
>
>   will push the required number of labels in the MPLS case.
>
>
>
>   For SRv6, the equivalent operation to the label push is to
>
>   insert an EH with the required SID list. The packet will already
>
>   have been encapsulated on the ingress PE and in the most
>
>   common Internet or VPN base use case it will not even have
>
>   an EH so that this EH insertion will result only in a single EH.
>
>
>
>   Alternatively, the PLR could also be configured to perform
>
>   encapsulation with a new IPv6 header using the repair SID
>
>   as IPv6 destination address, without needing any EH.
>
>   This will work for the vast majority of cases.
>
>   Remember that one 128-bit SID in SRv6 is in most cases
>
>   equivalent to 2 MPLS labels, i.e. a node label plus an
>
>   adjacency SID can be encoded in a single SRv6 SID.
>
>
>
>   Only in extreme cases would the PLR need to add an
>
>   EH to the new IPv6 header with more SIDs.
>
>
>
> - EH insertion for TI-LFA has nothing to do with stitching SRv6 domains.
>
>
>
> Hope it helps.
>
>
>
> Cheers
>
> Dirk
>
>
>
> Am 08.09.2019 um 09:19 schrieb Gyan Mishra <[e-mail]>:
>
>
>
> From reading through all the discussion threads the SR insertion is two fold one being for FRR capabilities using Ti-LFA or remote LFA tunnel so end up requiring double EH insertions on the Ingress PE tunnel head end SRv6 source node and then second scenario being a possible EH insertions occurrence on intermediate nodes.  I have not read through the drafts or RFC regarding Ti-LFA with SR but since that is an IGP extension I am guessing an opaque LSA and is not the traditional MPLS FRR link/node/path protection that adds an additional mpls shim so not sure why an EH insertion needs to occur for Ti-LFA.  Can someone clarify that use case for me.  Also the EH insertion on intermediate node what is the use case or reason for that.  My guess is it’s for special use case of stitching SRv6 domains together.  Please clarify..
>
>
>
>
>
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