Re: [Bier] WGLC: draft-ietf-bier-non-mpls-bift-encoding

["Jeffrey (Zhaohui) Zhang" <[e-mail]>]

I believe the spec is ready to progress beyond the WGLC.

Please see zzh> below for more comments.

> -----Original Message-----
> From: BIER [mailto:[e-mail]] On Behalf Of IJsbrand Wijnands
> (iwijnand)
> Sent: Monday, January 28, 2019 6:18 AM
> To: Xiejingrong <[e-mail]>
> Cc: Senthil Dhanaraj <[e-mail]>; BIER WG
> <[e-mail]>; Greg Shepherd <[e-mail]>
> Subject: Re: [Bier] WGLC: draft-ietf-bier-non-mpls-bift-encoding
> 
> Hi Senthil,
> 
> Thanks for the comments.
> 
> See response inline.
> 
> > I believe the ‘Domain-wide unique’ is the key value of Non-MPLS encapsulation.

Zzh> I don't think 'Domain-wide unique' is the KEY value of non-MPLS encapsulation. It's a simplification when you don't need the flexibility provided by non-unique BIFT-IDs.

> > Allocation BIFT-id locally on each node is an extra cost, not only in data-plane, but also in control-plane.

Zzh> I'll defer the advantage and data plane extra cost to later in this email, but control-plane is simple - all you need is a simple local allocation scheme, just like MPLS label allocation. It's a simple task compared to today's sophisticated routing/switching software.

> >
> > Support !
> > However, i would like to get couple of clarifications with respect to the BIFT-
> id in non-MPLS networks..
> >
> > 1.
> >
> > Excerpts from section 2.2.1.1 from RFC8296
> >    In an MPLS network, since the BIFT-id is an MPLS label, its value may
> >    be changed as a BIER packet goes from BFR to BFR.  In a non-MPLS
> >    network, since the BIFT-id is domain-wide unique, it is not expected    //
> Senthil
> >    to change as a BIER packet travels.
> >
> > Senthil// I believe, we do not want to mandate that the BIFT-id must be
> domain-wide-unique in case of non-MPLS networks (for the sake of flexibility).
> >               If its *not* domain-wide-unique, then the BIFT-id may change in
> BFR's as the BIER packet travels from BFIR to BFER.
> >               Authors & Fellow BIER'ers, let me know what do you think ?
> >
> > 2.
> >
> > draft-ietf-bier-non-mpls-bift-encoding-01 proposes two encoding methods
> for BIFT-id and is mentioned that, both of the encoding options are to derive
> "domain-wide-unique: BIFT-id's.
> >
> > I believe, option-2, that is  "6. The Non-MPLS Static IBU-SI BIFT Encoding", is
> flexible and can be used for non-domain-wide-unique BIFT-id's also.
> >
> > If we agree that, we should allow "non-domain-wide-unique" BIFT-id's for
> non-MPLS networks, can we re-phrase the text in draft-ietf-bier-non-mpls-
> bift-encoding-01 to specify that, such an encoding option can be used for non-
> domain-wide-unique cases as well ?
> 
> ICE: The 'IBU-SI BIFT Encoding’ is indeed flexible, but with that the flexibility is
> in the way you can add additional future arguments since the IBU is like a
> Label. But, allowing to change the IBU value from hop-by-hop like MPLS is
> adding a lot of complexity and we’re re-inventing MPLS. So lets keep this
> simple and domain side unique.

I agree that IBU-SI BIFT encoding should still be domain-wide unique encoding.

*** the following is not related to this WGLC ***
*** but I do want to take this opportunity to discuss it ***

I do agree that we should allow local BIFT-IDs just like in MPLS case; but for that the entire 20-bit should be changeable hop by hop (not just the "IBU" part as mentioned above).

In the early days of BIER, we went through significant effort to convince people the advantages of local label based BIFT-ID. It'd be a pity to see that lost in the non-MPLS case. As for additional complexity, it does not have to be implemented like label switching - perhaps just make the BIFT-ID change part of the BIER forwarding (but that's vendor specific). I don't think that's significant extra work compared to BIER lookup/forwarding logic.

If we could reach consensus on this early enough, non-MPLS hardware implementation for BIER may still be able to pick it up.

Jeffrey

> 
> Thx,
> 
> Ice.
> 
> 
> 
> >
> > Thanks,
> > Senthil
> >
> >
> > On Sat, Jan 26, 2019 at 1:43 AM Greg Shepherd <[e-mail]> wrote:
> >
> > Change of subject. This is WGLC for:
> >
> > https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__datatracker.ietf.org_doc_draft-2Dietf-2Dbier-2Dnon-2Dmpls-2Dbift-
> 2Dencoding_&d=DwIGaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-
> ndb3voDTXcWzoCI&r=f7wsLGcfzAWDNS6XNTBZwj_OLAOsZZqdrR2IDAzeZqE&
> m=0T5Q66dsW7YDHgsLXzVWk0n7Wqsnx_LH6Qa_ZEVVDEk&s=RDam3fmstw
> EzhanKQR5CKNHdENaisQ4gBoBX-CY_1X0&e=
> >
> > Same two week timer.
> >
> > Thanks
> >
> > On Fri, Jan 25, 2019 at 10:13 AM Greg Shepherd <[e-mail]> wrote:
> > Please read and reply to this thread with your vote for/against adoption of:
> >
> > https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__datatracker.ietf.org_doc_draft-2Dietf-2Dbier-2Dnon-2Dmpls-2Dbift-
> 2Dencoding_&d=DwIGaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-
> ndb3voDTXcWzoCI&r=f7wsLGcfzAWDNS6XNTBZwj_OLAOsZZqdrR2IDAzeZqE&
> m=0T5Q66dsW7YDHgsLXzVWk0n7Wqsnx_LH6Qa_ZEVVDEk&s=RDam3fmstw
> EzhanKQR5CKNHdENaisQ4gBoBX-CY_1X0&e=
> >
> > ..as a BIER WG document.
> >
> > This starts a two week counter.
> >
> > Thanks,
> > Chairs
> > (Shep)
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