Re: [Bier] [IANA #1359191] expert review for draft-ietf-bier-tether

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

Hi Chris,

“make BFRx and it's tunnels part of the normal routing domain” involves static tunnel configuration and announcement in BIER-specific routing topologies, and this draft talks about how to avoid that:

   For BFR1 to tunnel BIER packets to BFRx, the BFR1-BFRx tunnel need to
   be announced in Interior Gateway Protocol (IGP) as a forwarding
   adjacency so that BFRx will appear on the Shortest Path First (SPF)
   tree.  This needs to happen in a BIER specific topology so that
   unicast traffic would not be tunneled to BFRx.  Obviously this is
   operationally cumbersome.

   Section 6.9 of BIER architecture specification [RFC8279] describes a
   method that tunnels BIER packets through incapable routers without
   the need to announce tunnels.  However that does not work here,
   because BFRx will not appear on the SPF tree of BFR1.

   There is a simple solution to the problem though.  BFRx could
   advertise that it is X's helper and other BFRs will use BFRx (instead
   of X's children on the SPF tree) to replace X during its post-SPF
   processing as described in section 6.9 of BIER architecture
   specification [RFC8279].

Thanks.
Jeffrey




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From: Christian Hopps <[e-mail]>
Sent: Wednesday, March 6, 2024 10:12 AM
To: Jeffrey (Zhaohui) Zhang <[e-mail]>
Cc: Christian Hopps <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: Re: [Bier] [IANA #1359191] expert review for draft-ietf-bier-tether

[External Email. Be cautious of content]

I wasn't talking about BFR1. BFRx is a router, it's forwarding traffic to BFR[2-N] (over tunnel interfaces but the routing protocol doesn't care about this) why do you need anything more than that? I see no need for this extra technology. You simply make BFRx and it's tunnels part of the normal routing domain and let traffic flow from BFR1->X->BFRx->BFR[2-n] as you are trying to achieve, but without any new tech, just routing protocols and metrics.

Thanks,
Chris.


On Mar 6, 2024, at 08:37, Jeffrey (Zhaohui) Zhang <[e-mail]<mailto:[e-mail]>> wrote:

[- IANA]

Hi Chris,

The benefit of tethering is explained in Section 1. Specifically, in Figure 2:

                              ------ BFR2 ------- BFER2
                             /
      BFER1 ---  BFR1 ---- X ------- BFR3 ------- BFER3
                          / \  .........
                         /   \
                      BFRx    ------ BFRn ------- BFERn

W/o using tethering, BFR1 needs to tunnel multiple copies to BFR2/3/…/n individually, which may not be desired if the BFR1—X link is bandwidth-limited.
W/ BFRx being a helper tethered to X, BFR1 only tunnels one copy to BFRx. The link between BFRx and X could be a fat local pipe and it’s much better for BFRx to tunnel individual copies to BFR2/3/…/n.

BFRx is a normal router but it may not be in the normal path from BFR1 and BFR2/3/…/n so the tethering procedure is needed.
You can also view it as a form of TI-LFA: BFR1 tunnels packets to BFRx (as if X went down) that is not in the normal path who will then send to the final destinations.

Thanks.
Jeffrey

-----Original Message-----
From: BIER <[e-mail]<mailto:[e-mail]>> On Behalf Of Christian Hopps
Sent: Wednesday, March 6, 2024 5:33 AM
To: [e-mail]<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Bier] [IANA #1359191] expert review for draft-ietf-bier-tether

[External Email. Be cautious of content]


Allocating the code-point should not destabilize IS-IS itself so it's OK as far as that goes.

As an aside though, given a light read-through the draft's technology seems pretty questionable to me. A lot of complexity has been built here to place a router outside of the normal routing process and I don't understand why. This "helper" *router* could just be a normal BIER router in the domain and none of any of this would seem to be needed then.

Thanks,
Chris.



"David Dong via RT" <[e-mail]<mailto:[e-mail]>> writes:

> Dear Chris Hopps and Les Ginsberg (cc: bier WG),
>
> As the designated experts for the Sub-sub-TLVs for BIER Info Sub-TLV
> registry, can you review the proposed registration in draft-ietf-bier-tether-05 for us?
> Hannes has already approved this registration. Please see:
>
> https://datatracker.ietf.org/doc/draft-ietf-bier-tether/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-ietf-bier-tether/__;!!NEt6yMaO-gk!DpTdBx9peej8Kow_TsJSalAraH0LUB3AMqkuBS2WUSO7LSCljszS2G1-R6IL3dctFQ5FDkL9RxwW4Guk$>
>
> The due date assigned was March 1st.
>
> If this is OK, when the IESG approves the document for publication, we'll make the registration at:
>
> https://www.iana.org/assignments/isis-tlv-codepoints/<https://urldefense.com/v3/__https:/www.iana.org/assignments/isis-tlv-codepoints/__;!!NEt6yMaO-gk!DpTdBx9peej8Kow_TsJSalAraH0LUB3AMqkuBS2WUSO7LSCljszS2G1-R6IL3dctFQ5FDkL9R8udZ4B-$>
>
> We will act after all the experts have approved this registration, unless you tell us otherwise.
>
> With thanks,
>
> David Dong
> IANA Services Sr. Specialist
>
> On Mon Feb 26 18:43:14 2024, david.dong wrote:
>> Dear Chris Hopps and Les Ginsberg (cc: bier WG),
>>
>> As the designated experts for the Sub-sub-TLVs for BIER Info Sub-TLV
>> registry, can you review the proposed registration in
>> draft-ietf-bier-
>> tether-05 for us? Hannes has already approved this registration.
>> Please see:
>>
>> https://datatracker.ietf.org/doc/draft-ietf-bier-tether/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-ietf-bier-tether/__;!!NEt6yMaO-gk!DpTdBx9peej8Kow_TsJSalAraH0LUB3AMqkuBS2WUSO7LSCljszS2G1-R6IL3dctFQ5FDkL9RxwW4Guk$>
>>
>> The due date is March 1st.
>>
>> If this is OK, when the IESG approves the document for publication,
>> we'll make the registration at:
>>
>> https://www.iana.org/assignments/isis-tlv-codepoints/<https://urldefense.com/v3/__https:/www.iana.org/assignments/isis-tlv-codepoints/__;!!NEt6yMaO-gk!DpTdBx9peej8Kow_TsJSalAraH0LUB3AMqkuBS2WUSO7LSCljszS2G1-R6IL3dctFQ5FDkL9R8udZ4B-$>
>>
>> We will act after all the experts have approved this registration,
>> unless you tell us otherwise.
>>
>> With thanks,
>>
>> David Dong
>> IANA Services Sr. Specialist
>>
>> On Sun Feb 18 11:10:34 2024, [e-mail]<mailto:[e-mail]> wrote:
>> > Hi David,
>> >
>> > No concerns from my side to make the allocation.
>> >
>> > thanks,
>> >
>> > /hannes
>> >
>> > On Fri, Feb 16, 2024 at 10:26 PM David Dong via RT <
>> > [e-mail]<mailto:[e-mail]>> wrote:
>> >
>> > > Dear Chris Hopps, Hannes Gredler, Les Ginsberg (cc: bier WG),
>> > >
>> > > As the designated experts for the Sub-sub-TLVs for BIER Info Sub-
>> > > TLV registry, can you review the proposed registration in
>> > > draft-ietf-bier-tether-05 for us? Please see
>> > >
>> > > https://datatracker.ietf.org/doc/draft-ietf-bier-tether/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-ietf-bier-tether/__;!!NEt6yMaO-gk!DpTdBx9peej8Kow_TsJSalAraH0LUB3AMqkuBS2WUSO7LSCljszS2G1-R6IL3dctFQ5FDkL9RxwW4Guk$>
>> > >
>> > > The due date is March 1st.
>> > >
>> > > If this is OK, when the IESG approves the document for
>> > > publication, we'll make the registration at:
>> > >
>> > > https://www.iana.org/assignments/isis-tlv-codepoints/<https://urldefense.com/v3/__https:/www.iana.org/assignments/isis-tlv-codepoints/__;!!NEt6yMaO-gk!DpTdBx9peej8Kow_TsJSalAraH0LUB3AMqkuBS2WUSO7LSCljszS2G1-R6IL3dctFQ5FDkL9R8udZ4B-$>
>> > >
>> > > We will act after all the experts have approved this
>> > > registration, unless you tell us otherwise.
>> > >
>> > > With thanks,
>> > >
>> > > David Dong
>> > > IANA Services Sr. Specialist
>> > >
>> >


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