[Teas] Benjamin Kaduk's No Objection on draft-ietf-teas-assoc-corouted-bidir-frr-06: (with COMMENT)

Benjamin Kaduk <kaduk@mit.edu> Thu, 25 October 2018 03:12 UTC

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Subject: [Teas] Benjamin Kaduk's No Objection on draft-ietf-teas-assoc-corouted-bidir-frr-06: (with COMMENT)
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Benjamin Kaduk has entered the following ballot position for
draft-ietf-teas-assoc-corouted-bidir-frr-06: No Objection

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COMMENT:
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How does the unidirectional link failure logic and the revertive logic
interact?  That is, in the unidirectional failure case a node should be
detecting that there is a failure case and rerouting reverse traffic onto
the protection path to match the forward path.  But a node in the process
of reverting back on to the primary path (before its counterpart in the
other direction) would seem to observe the same packet/path behavior as in
the case of a unidirectional link failure.  Do we need to rely on the
flooding of link status information to differentiate between these cases?

Are the state-keeping and resource consumption burdens large for the
midpoint nodes that now must correlate whether they see traffic on
original/protection paths for associated flows?  (E.g., Section 4.1.3's
"when it receives the un-modified RSVP path messages and traffic".)
It seems like it should just be a linear scaling factor at worst, with no
real path to an attack, but perhaps there are security considerations
relating to router capacity.

Section 2

   In packet transport networks, there are requirements where the
   reverse LSP of a bidirectional LSP needs to follow the same path as
   its forward LSP [RFC6373].  [...]

Does this need a qualifier (e.g., "some packet transport networks" or
"there are sometimes requirements")?


Section 3.2

   tunnel S (on path B-F-G-D) to reach downstream MP node D whereas the
   upstream PLR node C reroute the protected reverse LSP2 traffic over
   the bypass tunnel N (on path C-I-H-A) to reach the upstream MP node
   A.  [...]

nit: "reroutes"

Section 4.1.1

   As shown in Figure 2, when using a node protection bypass tunnel with
   protected co-routed LSPs, asymmetry of paths can occur in the forward
   and reverse directions after a link failure [RFC8271].  In order to
   restore co-routing, the downstream MP node D (acting as an upstream
   PLR) SHOULD trigger the procedure to restore co-routing and reroute
   the protected reverse LSP2 RSVP Path messages and traffic over the
   bypass tunnel S (on path D-G-F-B) to the upstream MP node B upon

Why is this only a SHOULD?

Section 4.2

                                                        An endpoint node
   MAY set the Extended Association ID to the value shown in Appendix A.

The contents of Appendix A do not include a distinguished single value, but
rather a data structure, so I think that a phrase other than "to the
value" should be used.

   o  For double-sided provisioned bidirectional LSPs [RFC7551], both
      endpoints need to ensure that the bidirectional LSP has a unique
      Extended ASSOCIATION Object for each forward and reverse LSP pair
      by selecting appropriate unique Extended Association IDs signaled
      by them.

How does this signalling/selection process get the two endpoints to agree
on the same value?

Appendix A

(Again, "to the value" is not appropriate to describe the general format.
Perhaps, "to a value using the format".)

Please also explicitly describe the semantics of the "Reserved" field(s)
(i.e., set to zero on transmission and ignored on receipt).