I am an assigned INT directorate reviewer for
draft-ietf-bier-idr-extensions-16.txt. These comments were written primarily for
the benefit of the Internet Area Directors. Document editors and shepherd(s)
should treat these comments just like they would treat comments from any other
IETF contributors and resolve them along with any other Last Call comments that
have been received. For more details on the INT Directorate, see
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<https://datatracker.ietf.org/group/intdir/about/>.

This is a well-written document and I only have a few minor issues to mention:

1. Section 3 - The guidance provided that unknown or unsupported TLVs are to be ignored and propagated is appropriate, but implementations that do not implement this spec will not know that unless that behavior is standard for BGP. If it is standard, it would be useful to reference the RFC where that guidance is first documented.

2. Section 3 - Should "a BFR needs to include one BIER TLV for every Sub-domain that the prefix belongs to" be re-worded to use MUST?

3. Should there be mention of error checks to ensure that the TLVs do not cause the Update message to exceed the maximum allowable size (4K or 64K depending upon support for extended messages)?

4. Section 4 - I was expecting some mention of procedures in this section that describes how the BIER information is prevented from leaking out of an AS.

5. What harm is caused if BIER information is propagated outside of an administrative domain? Those should be listed in the Security Considerations section.