Last Call Review of draft-ietf-bess-evpn-mh-split-horizon-09
review-ietf-bess-evpn-mh-split-horizon-09-secdir-lc-sheffer-2024-06-30-00

This document defines a way to explicitly share the multi-homing split horizon
procedures over BGP, for a large variety of NVO use cases. This reviewer is not
familiar with the EVPN ecosystem, and comments below may reflect my own
ignorance.

In general: the document is clear, and does not appear to create any novel
security risks.

2.1: the first two paragraphs are duplicates.

2.2: "A received A-D per ES route where Single-Active and SHT bits are
different from zero MUST be treat-as-withdraw" - IIUC, this is very fragile
behavior, where an incorrect flag results in the entire path being removed. Why
does this behavior make more sense than simply ignoring the SHT bits?

2.2: For the Geneve use case: is the value "10" always valid, or is it only
valid if the ESI-Label is present? The text is unclear.

4: "The security considerations relevant to multihoming" - is it clear to all
readers which security considerations these are? Are you referring to the
entirety of Sec. 19 of RFC7432?

4: "unauthorized changes to the SHT configuration by an attacker should not
cause traffic disruption" - when various kinds of misconfiguration are "treat
as withdraw", how does that NOT cause traffic disruption? I would assume that
when the route is withdrawn, eventually traffic is disrupted.

7: the Contributors section is empty.