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

[Ron Bonica <[e-mail]>]

Tianran,

Should the IETF standardize two methods of encoding the same information because some networks have not deployed the older method? (yes/no)

Should the IETF standardize two methods of encoding the same information because some hardware platforms have never implemented the older method? (yes / no)

If the answer to either question is "yes", please explain why?

If the answer to both questions is "no", please explain why the SRH TLV for Alternate Marking is needed.

                                                                                                     Ron



Juniper Business Use Only

-----Original Message-----
From: Tianran Zhou <[e-mail]> 
Sent: Monday, November 15, 2021 8:03 PM
To: Ron Bonica <[e-mail]>; Tom Herbert <[e-mail]>
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: RE: [spring] A question for draft-fz-spring-srv6-alt-mark

[External Email. Be cautious of content]


Hi Ron,
Please see my reply in line.

Thanks,
Tianran

-----邮件原件-----
发件人: Ron Bonica [mailto:[e-mail]]
发送时间: 2021年11月16日 6:20
收件人: Tianran Zhou <[e-mail]>; Tom Herbert <[e-mail]>
抄送: [e-mail]; [e-mail]; [e-mail]
主题: RE: [spring] A question for draft-fz-spring-srv6-alt-mark

Folks,

The SRH TLV for Alternate Marking isn't needed because its meaning is identical to the AltMark Option when it appears in a Destination Options Header that precedes the SRH.

Arguments regarding the HBH are orthogonal to this issue. The HBH is processed at every node along a packet's deliver path, while the Destination Options header that precedes the SRH is processed " by the first destination that appears in the IPv6 Destination Address field plus subsequent destinations listed in the Routing header.

ZTR> This is clear to me. But this is not my point to propose the SRH TLV method.

Arguments regarding whether a complete IPv6 implementation must support the Destination Options header have already been settled by RFC 8200.

ZTR> I am sorry, I do not understand what do you mean hear. Could you please give more hint?

Arguments about whether it is easier to parse two smaller extension headers or one larger extension headers are not appropriate in the IETF, because they are platform dependent.

ZTR> My point is not about parsing two smaller EH vs. one larger EH. My point is the deployment when a network that support SRH but not support other EHs.


                                                                                                                  Ron







Juniper Business Use Only

-----Original Message-----
From: spring <[e-mail]> On Behalf Of Tianran Zhou
Sent: Friday, November 12, 2021 3:56 AM
To: Tom Herbert <[e-mail]>
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: Re: [spring] A question for draft-fz-spring-srv6-alt-mark

[External Email. Be cautious of content]


Hi Tom,

Firstly, the proposed solution follows the same logic as RFC8200, as in your text. So I do not see any problem. We just find another away to "ignore the options".
" RFC8200 relaxed the requirement for all nodes to process HBH options and acknowledged that this is reality. From an application perspective, if the TLVs can't be processed in a "fast path" it is best to ignore the options."

Secondly, I agree with the complexity of processing TLV. But we have already implemented the function with line rate. So the "core problem" from my perspective is how to deploy it.

We are always on the way to performance optimization. I've read your draft, and your solution is very interesting.

Best,
Tianran

-----Original Message-----
From: Tom Herbert [mailto:[e-mail]]
Sent: Friday, November 12, 2021 1:05 AM
To: Tianran Zhou <[e-mail]>
Cc: Joel M. Halpern <[e-mail]>; [e-mail]; [e-mail]; [e-mail]
Subject: Re: [spring] A question for draft-fz-spring-srv6-alt-mark

On Wed, Nov 10, 2021 at 10:48 PM Tianran Zhou <[e-mail]> wrote:
>
> Hi Tom,
>
> Please see my reply below.
>
> Best,
> Tianran
>
> -----邮件原件-----
> 发件人: Tom Herbert [mailto:[e-mail]]
> 发送时间: 2021年11月11日 2:32
> 收件人: Tianran Zhou <[e-mail]>
> 抄送: Joel M. Halpern <[e-mail]>; 
> [e-mail]; [e-mail]; [e-mail]
> 主题: Re: [spring] A question for draft-fz-spring-srv6-alt-mark
>
> 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.
>
> ZTR> It is true, but this is another story. RFC8200 is new, while RFC2460 has been widely deployed. The industry need time to evolve. I talked about the reality. The new proposal is motivated by the real deployment.
>
> 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.
>
> ZTR> We consider the incremental deployment case, or the deployment with multi-vendors. That means the supportive node could process SRH TLV well, while the non-supportive node could still transit. This is still valuable for operators to narrow down the scope when packet loss happens. This could also encourage the new tech development and deployment. I see this is very useful.

Tianran,

I think you're dancing around the core problem. Hardware implementations didn't support Hop-by-Hop options because they contain TLVs which are considered to be hard to process in a high performance datapath hardware pipeline. RFC2460 did mandate that all intermediate nodes need to process the HBH options which left hardware vendors with three choices: 1) process them in a software slow path and adhere to
RFC2460 2) ignore them altogether and violate RFC2460 3) drop the packet which technically adheres to RFC2460, but obviously kills any utility of feature. RFC8200 relaxed the requirement for all nodes to process HBH options and acknowledged that this is reality. From an application perspective, if the TLVs can't be processed in a "fast path" it is best to ignore the options.

So the underlying problem is in fact the complexity of processing TLVs in hardware datapath. Just replicating the same TLV mechanism in more protocols like SRH does nothing to help solve the problem. Until this is solved I don't believe we'll ever see TLVs being productively used in L3 (I suppose this might the anticipated industry evolution to which you referred). On the other hand if the problem is solved and a deployable an economical solution is presented that hardware vendors would adopt, then the problem would be solved for a whole class of use case (i.e. the same basic TLV construct is used in HBH, DestOpts, SRH, TCP options, IP options, UDP options, etc.).

If you're interested, I will be outlining the solution to this problem that we're working on in IPv6/v6ops meeting tomorrow.

Tom

>
> 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://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-6man-ipv6-alt-mark/__;!!NEt6yMaO-gk!Rer99s0DO7Ys6kR2kNbYfO5WFUh7DlH4ouzWfIp_chK7mPTLWcpo221rpmep31F9$ >?
> > >>>
> > >>>      Regards,
> > >>>
> > >>>      Greg
> > >>>
> > >>>
> > >>> ----------------------------------------------------------------
> > >>> --
> > >>> -- IETF IPv6 working group mailing list [e-mail] 
> > >>> Administrative
> > >>> Requests:
> > >>> https://urldefense.com/v3/__https://www.ietf.org/mailman/listinf
> > >>> o/ipv6__;!!NEt6yMaO-gk!Rer99s0DO7Ys6kR2kNbYfO5WFUh7DlH4ouzWfIp_c
> > >>> hK7mPTLWcpo221rprIfvSmZ$
> > >>> ----------------------------------------------------------------
> > >>> --
> > >>> --
> > >>>
> > >>
> > >> -----------------------------------------------------------------
> > >> --
> > >> - IETF IPv6 working group mailing list [e-mail] 
> > >> Administrative
> > >> Requests:
> > >> https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo
> > >> /ipv6__;!!NEt6yMaO-gk!Rer99s0DO7Ys6kR2kNbYfO5WFUh7DlH4ouzWfIp_chK
> > >> 7mPTLWcpo221rprIfvSmZ$
> > >> -----------------------------------------------------------------
> > >> --
> > >> -
> > >
> > > ------------------------------------------------------------------
> > > -- IETF IPv6 working group mailing list [e-mail] 
> > > Administrative
> > > Requests:
> > > https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/
> > > ipv6__;!!NEt6yMaO-gk!Rer99s0DO7Ys6kR2kNbYfO5WFUh7DlH4ouzWfIp_chK7m
> > > PTLWcpo221rprIfvSmZ$
> > > ------------------------------------------------------------------
> > > --
> > >
> >
> > _______________________________________________
> > spring mailing list
> > [e-mail]
> > https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/sp
> > ring__;!!NEt6yMaO-gk!Rer99s0DO7Ys6kR2kNbYfO5WFUh7DlH4ouzWfIp_chK7mPT
> > LWcpo221rpu4mP70S$
> >
> > --------------------------------------------------------------------
> > IETF IPv6 working group mailing list [e-mail] Administrative
> > Requests:
> > https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/ip
> > v6__;!!NEt6yMaO-gk!Rer99s0DO7Ys6kR2kNbYfO5WFUh7DlH4ouzWfIp_chK7mPTLW
> > cpo221rprIfvSmZ$
> > --------------------------------------------------------------------
_______________________________________________
spring mailing list
[e-mail]
https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/spring__;!!NEt6yMaO-gk!Rer99s0DO7Ys6kR2kNbYfO5WFUh7DlH4ouzWfIp_chK7mPTLWcpo221rpu4mP70S$