Subject: [spring] draft-ietf-idr-segment-routing-te-policy-05 - EXP NULL imposition

From: Przemyslaw Krol <[email-masked]>
Date: Sat, 30 Mar 2019 06:39:15 +0100

Greetings,

I have two *minor* comments regarding section 2.4.4

2.4.4.  Explicit NULL Label Policy Sub-TLV

 The policy signaled in this Sub-TLV MAY be overridden by local
      policy.

[pk] Wouldn't something like 'The behavior signaled in this Sub-TLV
MAY be overridden by local configuration/implementation/etc' be
better?

In this daft's context policy has a defined meaning and 'signalling a
policy' or 'local policy' may be confusing.

Also, do you find useful listing such local behaviors or is it too
implementation specific? The reason I'm asking is because I've seen 3
ways of handling automatic EXP NULL push (either available already or
in development/discussion):

- based on Endpoint's AF (if packet's AF doesn't match Endpoint's AF
-> PUSH EXP NULL)

- based on the AF of SIDs/labels in the Segment List (if packet's AF
doesn't match SID AF -> PUSH EXP NULL)

- always assume PUSH for IPv6 (which also means always assume
IPv4-only dataplane)

- always assume PUSH for IPv4 (which also means always assume
IPv6-only dataplane)

Each of these behaviors make assumptions depending on the primary use
case and perhaps having them documented (and potentially referred to
as Option A, Option B, etc or something similar) would help avoiding
confusion when discussing with vendors.

PS: I assume the Type number assignment will be handled by the ongoing
effort Ketan has mentioned in the context of policy name Sub-TLV but
just in case wanted to call this out too.

thanks,

pk

 --
Przemyslaw "PK" Krol |  Strategic Network Engineer ing | [email-masked]