[OPSAWG]Ketan Talaulikar's Discuss on draft-ietf-opsawg-discardmodel-14: (with DISCUSS)

[Ketan Talaulikar via Datatracker <[e-mail]>]

Ketan Talaulikar has entered the following ballot position for
draft-ietf-opsawg-discardmodel-14: Discuss

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DISCUSS:
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Thanks to the authors and the WG for their work on this document.

There are a few topics that I would like to discuss.

1) It is not clear to me whether this document considers MPLS traffic as L2 or
L3 (it is somewhat L2.5). Some aspects of L3 apply like "no route" but for MPLS
it should be "no ILM". Then again there is some coverage for SR-MPLS and
invalid-label under layer 3 so I am assuming it is considered under L3? In any
case, I was looking for some clarity and if discards for MPLS traffic would
benefit from their separate counters as opposed to putting them under L3. Under
L3, there is also address-family that covers IPv4 and IPv6 but not MPLS. There
are also cases where the MPLS label is disposed and inner IP packet processed
so we get multiple processing stages (see related point on double counting
further below). Same happens on the egress direction as well.

2) Regarding the following text:

5. A frame accounted for at Layer 2 MUST NOT be accounted for at Layer 3 and
vice versa. This is to avoid double counting.

I am assuming this is regarding discards. AFAIK packet reception would get
counted at both L2 and L3 layers? There are also some other similar
requirements for avoiding double counting which are not very clear to me. If we
take example of encapsulations (MPLS, IP-in-IP, etc.) then there can be
multiple layers of encapsulation that get disposed or imposed as the packet
traverses a router. How are they going to get accounted for in a manner that
avoids double counting?

3) Regarding unclear normative MUST in the following text:

9, When there are multiple reasons for discarding a packet, the ordering of
discard class reporting MUST be defined. Typically, this can be exposed by an
implementation by means of discard-order-capability.

I am not sure what "MUST be defined" means. It sounds vague for something that
is a MUST.

4) Regarding the following text, what about QoS based on IEEE 802.1Q PCP bits
or based on MPLS EXP bits ? What about QoS marking based on other than DSCP?

10. If Diffserv [RFC2475] is not used, no-buffer discards MUST be reported as
class[id="0"], which represents the default class.

5) Could you clarify what is meant by "origin" here?

14. Traffic to the device control plane (to-CPU) has its own class. Traffic
from the device control plane (from-CPU) is accounted for by origin,
independent of the forwarding mechanism (e.g., any egress policer it
traverses), and MUST also be accounted for in the same way as other egress
traffic.