[Tsv-art] Tsvart early review of draft-ietf-idr-bgp-ct-srv6-03

[Joseph Touch via Datatracker <[e-mail]>]

Reviewer: Joseph Touch
Review result: Not Ready

This document was reviewed as per the following request:

TSV-DIR - Please look at this draft from the viewpoint of having intent (color)
aware customer traffic forwarded over a VPN overlay (tunnels) that forwarded
over a set of intent (color) aware underlay of tunnels.  Please consider the
problems with tunnels in your review of this text.

The document refers to these tunnels in a manner that appears consistent with
draft-ietf-idr-bgp-ct. As a side note, it would be preferable for this document
to refer to the terminology of this bgp-ct draft rather than repeating it, so
it would be more clear which terms are introduced herein. Avoiding duplication
also avoids the need to align the two sets of definitions upon publication.

TSV-DIR area of concern appears to originate in the bgp-ct draft rather than
herein. There are a variety of issues with tunnels not addressed in either
document, many of which are described in draft-ietf-intarea-tunnels (though not
refreshed, this remains an active INTAREA doc), notably the difference between
tunnel path MTU, tunnel egress MTU, and overall path MTU of the tunneling
service (which is dependent on the latter rather than the former), especially
the difficulty in determining the tunnel path MTU. The way in which both
documents refer to tunneling as (IMO) 'do a tunnel, whatever that involves' is
a bit of a disconnect with the idea that these tunnels, when deployed, provide
service assurances on which upper layers can plan. In particular, Section 4.1
of the bgp-ct doc gives some potentially relevant examples, but only for a
subset of the tunneling technologies described in the definition.

Both documents would benefit from a more precise definition of the tunnel
technologies that have properties needed to support these methods. In
particular, a tunnel cannot provide "transport class aware" services unless
that can be assured by the layer over which the tunnel operates or by the
tunnel protocol itself. E.g., a tunnel cannot provide guaranteed BW over a
best-effort network, but a tunnel can create assured in-order delivery over an
underlay without such ordering guarantees.