Re: [lisp] [spring] IPv6-compressed-routing-header-crh

[Greg Mirsky <[e-mail]>]

Hi Tom,
in draft-mirsky-6man-unified-id-sr
<https://tools.ietf.org/html/draft-mirsky-6man-unified-id-sr-02> we've
proposed the use of 20 and 32 bits-long SIDs in SR EH. Two bits-long field
also defined in the Flags to identify the length of SID element in the SR
EH:
      0b00 - 128-bits SID;
      0b01 - 20-bits SID;
      0b10 - 32-bits SID
      0b11 - reserved for future use.

Much appreciate your comments on that draft, suggestions.

Regards,
Greg


On Fri, Apr 12, 2019 at 3:09 PM Tom Herbert <[e-mail]> wrote:

> On Fri, Apr 12, 2019 at 1:48 PM Mark Smith <[e-mail]> wrote:
> >
> > Hi Tom,
> >
> > On Sat, 13 Apr 2019 at 00:26, Tom Herbert <[e-mail]> wrote:
> > >
> > > On Sun, Mar 31, 2019 at 7:40 AM Robert Raszuk <[e-mail]>
> wrote:
> > > >
> > > > Hi Mark,
> > > >
> > > > > As MPLS SR SIDs are 20 bits, then rounding up to an octet boundary
> and a 32 bit alignment,
> > > > > I'd think 32 bit SIDs would be adequate to perform SR in an IPv6
> network.
> > > > >
> > > > > As 32 bit SIDs are also the same size as IPv4 addresses, that may
> also create some opportunities to
> > > > > leverage IPv4 support in existing protocols to suite carrying and
> processing 32 bit SIDs with some, possibly
> > > > > slight, modification. For example, perhaps IPv4 Address Family
> support in OSPFv3 (RFC 5838) could be
> > > > > somehow leveraged to suit SR.
> > > >
> > > >
> > > > Thank you for describing your understanding of fundamentals of SR.
> > > >
> > > > I think SR while indeed started with the story of "less control
> plane is good for you" now clearly has evolved into not only reduction of
> control plane but what can be even more important to some users ability to
> request specific behavior via programmed functions of network elements on a
> per flow basis without actually per flow or per path signalling or state.
> > > >
> > > > Yes for some it may be very useful feature and I am sure some will
> call it overload of data plane or . There is no one size fits all.
> > > >
> > > > With that let's observe that till today SR did not require any new
> mapping plane to be distributed in control plane and to be inserted into
> data plane. This is clearly a precedent.
> > > >
> > > > Furthermore as we see in companion documents all additional network
> functionality is being taken away from SRH and is being shifted to
> Destination Options .
> > > >
> > > > As far as mapping plane I already pointed out in my Vector Routing
> proposal that we have one already it is called BGP. One needs to also
> observe that we as industry worked number of years of protocol suite called
> LISP allowing not only very good mapping plane, but also data plane
> integration. CC-ing lisp authors for their comments. Note also work for
> integrating SRv6 with LISP which is already is published.
> > > >
> > > > Since you correctly observed that now SID can be 32 bit and that is
> similar to the size of IPv4 my fundamental question is why not use
> something which already exists instead of defining some sort of new  from
> scratch ?
> > > >
> > > Robert,
> > >
> > > I don't see in the SRH draft where 32 bit SIDs are defined. Can you
> > > please provide a reference?
> > >
> >
> > To clarify, I've been thinking about the idea of a smaller SID size
> > for IPv6 for a while now (since inserting EHs came up), and thought
> > about what would be a generic single size that might suit SR that
> > wasn't the same size as an IPv6 address. 32 bits seemed suitable to
> > me, although if people wanted bigger, I'd be suggesting 64 bits (not
> > entirely coincidentally the common IID size.)
> >
> > Ron and others have written this draft, which supports SIDS of various
> > sizes - 8, 16 or 32 bits - that triggered this discussion.
> >
> Mark,
>
> Why not just put a SID length field in the header (like RFC6554 but
> more generic). That would allow lengths of 1-16 bytes. Additional
> flags could be used to indicate the semantics of the entries. For
> instance, they might be actual addresses (128 bits for IPv6, 32 bits
> for IPv4), parts of addresses (prefixes of suffixes like in RFC6554)
> where the rest of the address can be inferred, indices into a table,
> labels, etc.
>
> Tom
>
> > "The IPv6 Compressed Routing Header (CRH)"
> > https://tools.ietf.org/html/draft-bonica-6man-comp-rtg-hdr-03
> >
> > Regards,
> > Mark.
> >
> >
> > > As for trying to use something that already exists, why does SR used a
> > > fixed size format for SIDs instead of a variable length format like
> > > that described in RFC6554? Similarly, why does SR define it's own TLV
> > > format instead of using Hop-by-Hop and Destination Options defined in
> > > RFC8200?
> > >
> > > Tom
> > >
> > > > It will be perfectly fine to have full proper SRv6 with SRH and LISP
> or Vector Routing as an alternative options. I really do not see a room or
> need for yet one more mapping plane. What problem does it solve which would
> not be already solved elsewhere ?
> > > >
> > > > Kind regards,
> > > > Robert
> > > >
> > > >
> > > >>> 2) Is there an agreement that solutions which require additional
> per SR path state in both control plane and now in data plane are really
> something we should be endorsing here ?
> > > >>
> > > >>
> > > >> I think so.
> > > >>
> > > >> My understanding of what SR is fundamentally about is to reduce
> control plane state and processing. The trade-off for reduced control plane
> state and processing is to instead carry and encode most or all of that
> information or its semantics as per-packet overhead.
> > > >>
> > > >> If the per-packet overhead becomes too large and expensive, then
> pushing some of that information and processing back into the control plane
> should be ok, as long as there is still a beneficial overall reduction in
> control plane state and processing.
> > > >>
> > > >> As MPLS SR SIDs are 20 bits, then rounding up to an octet boundary
> and a 32 bit alignment, I'd think 32 bit SIDs would be adequate to perform
> SR in an IPv6 network.
> > > >>
> > > >> As 32 bit SIDs are also the same size as IPv4 addresses, that may
> also create some opportunities to leverage IPv4 support in existing
> protocols to suite carrying and processing 32 bit SIDs with some, possibly
> slight, modification. For example, perhaps IPv4 Address Family support in
> OSPFv3 (RFC 5838) could be somehow leveraged to suit SR.
> > > >>
> > > >> Regards,
> > > >> Mark.
> > > >
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