Re: Adoption Call for "The IPv6 Compact Routing Header (CRH)"

[Gyan Mishra <[e-mail]>]

I believe a few variants of what you propose have been done with the SRV6
compression drafts.

Gyan

On Thu, May 28, 2020 at 10:30 PM Wang, Weibin (NSB - CN/Shanghai) <
[e-mail]> wrote:

> I think it is a good idea to create a new routing type for encoding new
> type of SID in RH.
>
> I also think that, as a result of IPv6 address has 16 bytes length, its
> space is big enough, lots of bits-string within it is redundant and
> unnecessary in some scenario. so considering the classic SRv6 scenario, we
> can only use least significance 64 bits within a fixed /64 prefix block for
> all SID assigning for limited domain being deployed by SRv6.
> That means, only one same  /64 block is enough for all kind of SIDs
> assigning within limited domain, so only rightmost 64 bits representing all
> SIDs allocated to all prefix-SID and Adj-SIDs and Service-SIDs should be
> encoded within SRH with new routing type value. During packets being
> encapsulated with outer IPv6 and new RH forwarding through SRv6 domain, its
> left-most 64 bits of DA field keep intact and only right-most 64 bits will
> be replaced endpoint by endpoint from SRH.SL.
> The benefit:
> - get half-reduced SRH length compared to classic SRv6 SRH under same
> number of SIDs encoded segment list;
> - keep same forwarding plane with classic SRH processing; no extra
> processing for deducing compressed SID or normal SID coding in SRH; keeping
> the simple of forwarding plane is most important for all solution.
> - only one /64 prefix as SID block, the complexity level of security
> deployment is largely reduced.
> - the efforts of control plane protocol extension such as ISIS-srv6 or
> OSFP-srv6 have being made previously can be reserved.
> - no mapping mechanism at forwarding procedure and control plane.
> - the solution is balance between SRH size and complexity of forwarding
> plane.
>
>
> Cheers!
>
> Wang Weibin
>
> -----Original Message-----
> From: ipv6 <[e-mail]> On Behalf Of Tom Herbert
> Sent: 2020年5月29日 4:48
> To: Greg Mirsky <[e-mail]>
> Cc: IPv6 List <[e-mail]>; Ran Pang(联通集团联通网络技术研究院本部) <
> [e-mail]>
> Subject: Re: Adoption Call for "The IPv6 Compact Routing Header (CRH)"
>
> On Thu, May 28, 2020 at 1:23 PM Greg Mirsky <[e-mail]> wrote:
> >
> > Hi Tom,
> > I agree that "and ignored on receipt" in the definition of the Flags
> field makes the future use of the field more restrictive. But I believe
> that can be mitigated, as I've mentioned earlier, via control and/or
> management plane extensions. Not that we have not faced a similar situation
> before and dealt with the challenge in a reasonable way.
>
> Or just create a new routing type that is universally unambiguous, doesn't
> require external information just to understand the header format, and
> carries not risk of breaking backwards compatibility. Like Joel said, being
> compatible with SRH routing type for compressed SIDs isn't a requirement
> and I can think of any reason why it should be. A new routing type is also
> an opportunity to revisit all the fields in the header, for instance we can
> reevaluate whether Flags, Tags, and TLVs are really needed in a routing
> header.
>
> Tom
>
> >
> > Regards,
> > Greg
> >
> > On Thu, May 28, 2020 at 1:14 PM Tom Herbert <[e-mail]> wrote:
> >>
> >> On Thu, May 28, 2020 at 12:54 PM Greg Mirsky <[e-mail]>
> wrote:
> >> >
> >> > Hi Tom,
> >> > you've noted that "The format of SRH is very specific that SIDs are
> 128 bits". True, that is the view, the current view based on the definition
> of SRv6 and SRH in  RFCs 8402 and 8754. But both may be updated at some
> point. Thus we can avoid the introduction of RH per SID length. Would you
> agree that it is a viable option?
> >>
> >> Greg,
> >>
> >> Unfortunately it's not an option. There is no field in SRH that could
> >> robustly be used as a code point to indicate an alternate header
> >> format or different length of SIDs. Neither is there any way to
> >> retroactively add that this since RFC8754 is already out the door and
> >> in deployment. This is analogous to someone wanting to create a
> >> compressed version of the IPv6 header to use 64-bits instead of 128
> >> bit addresses-- there is no way to do that without getting a new IP
> >> version number. The difference in the analogy, is that the IP version
> >> number space is only4 bits, but the routing type space is 8 bits. So
> >> allocating new routing types for compressed SIDs really isn't much
> >> issue since there are plenty of values available (247 routing type
> >> values are unassigned whereas only 5 IP version numbers are
> >> unassigned).
> >>
> >> Tom
> >>
> >> >
> >> > Regards,
> >> > Greg
> >> >
> >> > On Thu, May 28, 2020 at 11:33 AM Tom Herbert <[e-mail]>
> wrote:
> >> >>
> >> >>
> >> >>
> >> >> On Thu, May 28, 2020, 11:22 AM Joel M. Halpern <[e-mail]>
> wrote:
> >> >>>
> >> >>> Several people, including at least one I-D, have asserted that
> >> >>> there is some abstract requirement for compatibility with SRvc6's
> >> >>> SRH.  There is no such requirement.  That is not a criterion the
> >> >>> 6man group needs to consider.  In my personal opinion, it is not
> >> >>> even a constraint on what SPRING chooses to do.
> >> >>
> >> >>
> >> >> Joel,
> >> >>
> >> >> It's not even clear what compatibility with SRH means. The format of
> SRH is very specific that SIDs are 128 bits, and the protocol has no
> sufficient extensibility mechanism that allows that to change without
> breaking backwards compatibility. As far as I can tell, changing or
> compressing SIDs requires a new routing type regardless of the compression
> method or who specifies it.
> >> >>
> >> >> Tom
> >> >>
> >> >>>
> >> >>> Yours,
> >> >>> Joel
> >> >>>
> >> >>> On 5/28/2020 3:38 AM, Ran Pang(联通集团联通网络技术研究院本部) wrote:
> >> >>> > Hi WG,
> >> >>> >
> >> >>> > It seems like CRH is not compatible with SRv6 and SRH. We need
> >> >>> > to discuss how CRH cooperates with uSID, G-SRv6 or other SRv6
> >> >>> > header compression solutions before adoption, or whether CRH
> >> >>> > will cause difficulties in the deployment of G-SRv6 and other
> >> >>> > solutions. At present, we tend to choose solutions compatible
> with SRH.
> >> >>> >
> >> >>> >
> >> >>> > Thanks,
> >> >>> >
> >> >>> > Ran
> >> >>> >
> >> >>> >
> >> >>> >     *From:* Bob Hinden <mailto:[e-mail]>
> >> >>> >     *Date:* 2020-05-16 06:13
> >> >>> >     *To:* IPv6 List <mailto:[e-mail]>
> >> >>> >     *CC:* Bob Hinden <mailto:[e-mail]>
> >> >>> >     *Subject:* Adoption Call for "The IPv6 Compact Routing Header
> (CRH)"
> >> >>> >     This message starts a two-week 6MAN call on adopting:
> >> >>> >     Title:          The IPv6 Compact Routing Header (CRH)
> >> >>> >     Authors:        R. Bonica, Y. Kamite, T. Niwa, A. Alston, L.
> Jalil
> >> >>> >     File Name:      draft-bonica-6man-comp-rtg-hdr-21
> >> >>> >     Document date:  2020-05-14
> >> >>> >     https://tools.ietf.org/html/draft-bonica-6man-comp-rtg-hdr
> >> >>> >     as a working group item. Substantive comments regarding
> adopting
> >> >>> >     this document should be directed to the mailing list.
> Editorial
> >> >>> >     suggestions can be sent to the authors.
> >> >>> >     Please note that this is an adoption call, it is not a w.g.
> last
> >> >>> >     call for advancement, adoption means that it will become a
> w.g.
> >> >>> >     draft.  As the working group document, the w.g.. will decide
> how the
> >> >>> >     document should change going forward.
> >> >>> >     This adoption call will end on 29 May 2020.
> >> >>> >     The chairs note there has been a lot of discussions on the
> list
> >> >>> >     about this draft.   After discussing with our area directors,
> we
> >> >>> >     think it is appropriate to start a working group adoption
> call.  The
> >> >>> >     authors have been active in resolving issues raised on the
> list.
> >> >>> >     Could those who are willing to work on this document, either
> as
> >> >>> >     contributors, authors or reviewers please notify the list.
>  That
> >> >>> >     gives us an indication of the energy level in the working
> group
> >> >>> >     to work on this.
> >> >>> >     Regards,
> >> >>> >     Bob and Ole
> >> >>> >
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*Gyan Mishra*

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