Re: [spring] A question for draft-fz-spring-srv6-alt-mark

[Tom Herbert <[e-mail]>]

On Tue, Nov 9, 2021 at 7:41 PM Tianran Zhou <[e-mail]> wrote:
>
> Hi Joel,
>
> I do not need to assume a device that support SRH will support this new TLV.
> We only assume the device that do not support this new TLV can ignore and bypass the packet, not to drop.
> I see text from RFC8754 section 2.1.
> " all TLVs are ignored unless local configuration indicates otherwise "
> " Thus, TLV and HMAC support  is optional for any implementation "
> " Type Length Value (TLV) entries contain OPTIONAL information that may
>    be used by the node identified in the Destination Address (DA) of the
>    packet. "
> " The Length field of the TLV is used to skip the TLV while inspecting
>    the SRH in case the node doesn't support or recognize the Type. "
>
> My understanding on SRH can support my assumption.

Tianran,

RFC8200 allows intermediate nodes to ignore TLVs in HBH options, and I
did propose allowing intermediate destinations to ignore destination
options before the routing header in draft-herbert-ipv6-update-opts.

But allowing nodes to ignore TLVs only mitigates the problems of
packet loss in the presence of TLVs; the obvious purpose of defining a
new TLV is that it _will_ be processed, lest the host sender is just
wasting cycles and bandwidth sending bits no one looks at. If all
implementations of SRH ignore TLVs then defining the TLV is pointless
(AFAIK only Linux and maybe VPP software implementations support SRH
TLVs). For the purposes of actually processing a TLV, like alt mark, I
still don't see any advantage to putting this in SRH as opposed to
Destination options or HBH options.

Tom

>
> Best,
> Tianran
>
> -----Original Message-----
> From: spring [mailto:[e-mail]] On Behalf Of Joel M. Halpern
> Sent: Wednesday, November 10, 2021 10:38 AM
> To: Tianran Zhou <[e-mail]>
> Cc: [e-mail]; [e-mail]; [e-mail]
> Subject: Re: [spring] A question for draft-fz-spring-srv6-alt-mark
>
> (Again, speaking as  participant.)
> You seem to be assuming that devices (hard or soft) that support SRH will support this new TLV.  It is not obvious that they will support any SRH TLVs.  And if they do, they clearly will not support a not yet defined TLV.
>
> Yours,
> Joel
>
> On 11/9/2021 9:04 PM, Tianran Zhou wrote:
> > Hi Tom,
> >
> > All you arguments are correct.
> > If a network is built all by supportive devices (support HbH, DoH), there is no doubt that 6man-alt-mk is a sound solution.
> >
> > However, existing network may consist many non-supportive devices.
> > These devices may 1. support SRH, but not HbH and DoH. This is the current situation about most chip vendors.
> > 2. some vendors may not want to support HbH and DoH in near future.
> >
> > Then, how to deploy alt-mk in these network?
> > The way is to bypass those non-supportive nodes without packet drop.
> >
> > This is why SRH TLV based spring-srv6-alt-mark is proposed.
> >
> > Best,
> > Tianran
> >
> > -----Original Message-----
> > From: ipv6 [mailto:[e-mail]] On Behalf Of Tom Herbert
> > Sent: Tuesday, November 9, 2021 11:41 PM
> > To: Joel M. Halpern <[e-mail]>
> > Cc: [e-mail]; [e-mail];
> > [e-mail]
> > Subject: Re: A question for draft-fz-spring-srv6-alt-mark
> >
> > On Tue, Nov 9, 2021 at 7:31 AM Joel M. Halpern <[e-mail]> wrote:
> >>
> >> Let me try phrasing the question about the SRH TLV in a different way.
> >> And this is as a participant, not as co-chair.
> >> Assumptions as I understand them:
> >>
> >> 1) The 6man draft requires support of both the HbH and DoH cases
> >> 2) Any node supporting the SRH altMarking can be assumed to also
> >> support the 6man altMark
> >>
> >> If assumption 2 is accurate, then it seems to me that adding the SRH
> >> TLV adds complexity to save a few bits without adding any capability.
> >> This strikes me as a bad trade.
> >
> > +1
> >
> > Also, destination and hop-by-hop options have the advantage that they work with any other extension header or protocol. SRH TLVs only work in the narrow use case of SRv6 and don't help router headers that might be defined.
> >
> > Tom
> >
> >>
> >> Yours,
> >> Joel
> >>
> >> On 11/8/2021 2:28 PM, Giuseppe Fioccola wrote:
> >>> Hi Greg,
> >>>
> >>> Yes, with DOH + SRH, the end node of a segment should still conform
> >>> to RFC8200, based on the discussion in 6MAN.
> >>>
> >>> The proposal to use HBH is also mentioned in draft-ietf-6man-ipv6-alt-mark.
> >>>
> >>> Regards,
> >>>
> >>> Giuseppe
> >>>
> >>> *From:* Greg Mirsky <[e-mail]>
> >>> *Sent:* Monday, November 8, 2021 6:17 PM
> >>> *To:* Giuseppe Fioccola <[e-mail]>
> >>> *Cc:* [e-mail]; [e-mail];
> >>> [e-mail]
> >>> *Subject:* Re: A question for draft-fz-spring-srv6-alt-mark
> >>>
> >>> Hi Giuseppe,
> >>>
> >>> thank you for the clarification.
> >>>
> >>> I was considering the DOH+SDH but am not sure if the end node of a
> >>> segment conforms to the note attributed to DOH in RFC 8200:
> >>>
> >>>      note 3: for options to be processed only by the final destination of
> >>>      the packet.
> >>>
> >>> I recall the discussion in 6man WG but not the final conclusion of it.
> >>>
> >>> My proposal to use HbH EH included the use of the management plane
> >>> to explicitly enable AltMarking only on segment end-points and keep
> >>> it disabled on transit nodes.
> >>>
> >>> Regards,
> >>>
> >>> Greg
> >>>
> >>> On Mon, Nov 8, 2021 at 8:50 AM Giuseppe Fioccola
> >>> <[e-mail] <mailto:[e-mail]>> wrote:
> >>>
> >>>      Hi Greg,
> >>>
> >>>      The use of HbH EH does not fit well in the case of SRH. Indeed, with
> >>>      the AltMark HbH Option, it is possible to monitor every router on
> >>>      the path with feature enabled, so it potentially allows the
> >>>      measurement to every nodes in the path and not only to the nodes
> >>>      that are identities in the SR path.
> >>>
> >>>      While, with the Destination Option preceding a Routing Header, it is
> >>>      possible to apply the measurement to every destination node in the
> >>>      route list. This means that, whenthe AltMark Destination Option
> >>>      precedes the SRH, it allows the measurement for all the nodes that
> >>>      are identities in the SR path.
> >>>
> >>>      The solution with SRH TLV is equivalent to DOH + SRH, but it can be
> >>>      an optimized solution for SRH since it leverages the SRH TLV
> >>>      capability, without adding an additional EH that can be a problem in
> >>>      some cases.
> >>>
> >>>      Regards,
> >>>
> >>>      Giuseppe
> >>>
> >>>      *From:* Greg Mirsky <[e-mail]
> >>>      <mailto:[e-mail]>>
> >>>      *Sent:* Monday, November 8, 2021 2:57 PM
> >>>      *To:* Giuseppe Fioccola <[e-mail]
> >>>      <mailto:[e-mail]>>
> >>>      *Cc:* [e-mail]
> >>>      <mailto:[e-mail]>; [e-mail]
> >>>      <mailto:[e-mail]>; [e-mail] <mailto:[e-mail]>
> >>>      *Subject:* Re: A question for draft-fz-spring-srv6-alt-mark
> >>>
> >>>      Hi Giuseppe,
> >>>
> >>>      thank you for the detailed explanation of what the authors consider
> >>>      as the problem. In the presentation, you've mentioned that the new
> >>>      AltMark SRH TLV allows for better control of which nodes along an SR
> >>>      Policy participate in the measurement. I imagine that the HbH IPv6
> >>>      extension header that includes the AltMark TLV can be used to
> >>>      achieve the same result if only SR nodes are enabled for the AltMark
> >>>      processing. What do you think of using the HbH EH? Am I missing
> >>>      something?
> >>>
> >>>      Regards,
> >>>
> >>>      Greg
> >>>
> >>>      On Mon, Nov 8, 2021 at 1:13 AM Giuseppe Fioccola
> >>>      <[e-mail] <mailto:[e-mail]>>
> >>>      wrote:
> >>>
> >>>      Hi Greg,
> >>>
> >>>      Thank you for your comment.
> >>>
> >>>      It is very good to have your support on this draft.
> >>>
> >>>      draft-ietf-6man-ipv6-alt-mark defines the AltMark DOH. In case of
> >>>      SRH, DOH + SRH can be used to implement the measurement for every
> >>>      node that is an identity in the SR path.
> >>>
> >>>      But, the approach with DOH + SRH requires two extension headers and
> >>>      this can have operational implications.
> >>>
> >>>      The goal of this draft is to find an optimized solution that best
> >>>      suits for SRH. Therefore we propose to use the SRH TLV. If accepted,
> >>>      this document would update draft-ietf-6man-ipv6-alt-mark only for SRv6:
> >>>
> >>>      - in case of SRH there would be a single way to apply AltMark
> >>>      through SRH TLV,
> >>>
> >>>      - while for all the other cases with IPv6 data plane the use of the
> >>>      HbH and DOH is the only choice to carry AltMark data fields.
> >>>
> >>>      Regards,
> >>>
> >>>      Giuseppe
> >>>
> >>>      *From:* Greg Mirsky <[e-mail]
> >>>      <mailto:[e-mail]>>
> >>>      *Sent:* Sunday, November 7, 2021 9:01 PM
> >>>      *To:* [e-mail]
> >>>      <mailto:[e-mail]>; [e-mail]
> >>>      <mailto:[e-mail]>; [e-mail] <mailto:[e-mail]>
> >>>      *Subject:* A question for draft-fz-spring-srv6-alt-mark
> >>>
> >>>      Dear Authors et al.
> >>>
> >>>      thank you for this document. I am supporting and following the work
> >>>      on the Alternate Marking method in various IETF WGs. What do you see
> >>>      as the benefits of defining a new SRH TLV for the Alternate Marking
> >>>      method compared to solutions defined for IPv6 in
> >>>      draft-ietf-6man-ipv6-alt-mark
> >>>      <https://datatracker.ietf.org/doc/draft-ietf-6man-ipv6-alt-mark/>?
> >>>
> >>>      Regards,
> >>>
> >>>      Greg
> >>>
> >>>
> >>> --------------------------------------------------------------------
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