Re: [Gen-art] [Bier] Genart last call review of draft-ietf-bier-tether-04

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

Hi Joel,

Thanks for your review and comments.
Please see zzh> below.


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Reviewer: Joel Halpern
Review result: Ready with Issues

I am the assigned Gen-ART reviewer for this draft. The General Area Review Team (Gen-ART) reviews all IETF documents being processed by the IESG for the IETF Chair.  Please treat these comments just like any other last call comments.

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Document: draft-ietf-bier-tether-04
Reviewer: Joel Halpern
Review Date: 2024-02-15
IETF LC End Date: 2024-02-29
IESG Telechat date: Not scheduled for a telechat

Summary: This document is almost ready for publication as a proposed standard

Major issues:
    Section 3.1 on IGP Signaling states "The helper node (BFRx) MUST advertise
    one or more BIER Helped Node sub-sub-TLVs".  However, I only find a vague
    outline of this sub-sub TLV.  The code point for it is requested in the
    IANA considerations section, but the description is a single sentence
    easily misread and lacking the conventional diagrams and precision that is
    used to define routing TLVs (and sub or sub-sub TLVs.)

zzh> Point taken. How about the following?

   Suppose that the BIER domain uses BIER signaling extensions to ISIS
   [RFC8401] or OSPF [RFC8444].  The helper node (BFRx) MUST advertise
   one or more BIER Helped Node sub-sub-TLVs in the BIER Info sub-TLV in
   the case of ISIS or BIER Helped Node sub-TLVs in the BIER sub-TLV in
   the case of OSPF, one for each helped node:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Type       |   Length      |    Priority   |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Address of the Helped Node                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type is TBD1 (in the case of ISIS) or TBD2 (in the case of OSPF).
   The Value field starts with a one-octet Priority field, followed by a
   one-octet Reserved field, and then the Address of the Helped Node
   (X).  The Length is 6 for IPv4 and 18 for IPv6 respectively.


Minor issues:
    In the paragraph about multiple helpers helping a single non-supporting
    router, I think I missed how one case works properly.  (Section 2,
    additional considerations, paragraph 6).  The text says that the sending
    BFR (BFR1 can choose to use multiple helpers if they are available.
    Assuming that BFR1 chooses to use BFR2 and BFR 3 to reach BFRs 4 .. BFR N,
    the text is clear that this results in BFR2 and BFR 3 both sending copies
    of the packet to Router X.  That is fine.  It is load, but it is a
    tradeoff.  However, it appears that both BFR2 and BFR 3 would send packets
    to BFR4, and to all the other BFR children of X.  This results in duplicate
    packets in the rest of the tree.  Is there some assumption I missed that
    prevents this?

Zzh> The BIER forwarding algorithm ensures that the two copies of the same packet that a BFR sends out never have overlapping bits in the BitString. Therefore, no duplication will happen.
Zzh> Thanks!
Zzh> Jeffrey

Nits/editorial comments:


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