[Bier] Genart last call review of draft-ietf-bier-tether-04

[Joel Halpern via Datatracker <[e-mail]>]

Reviewer: Joel Halpern
Review result: Ready with Issues

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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.)

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?

Nits/editorial comments: