Early Review of draft-ietf-pce-pcep-yang-08
review-ietf-pce-pcep-yang-08-yangdoctors-early-jethanandani-2018-11-26-00

Document reviewed: draft-ietf-pce-pcep-yang-08

I am not an expert in PCEP. This review is looking at the draft from a YANG
perspective. With that said, I have marked it as “On the Right Track” because
of some of the points discussed below.

Summary:

This document defines a YANG data model for the management of Path Computation
Element communications Protocol (PCEP) for communications between a Path
Computation Client (PCC) and a Path Computation Element (PCE), or between two
PCEs.  The data model includes configuration data and state data (status
information and counters for the collection of statistics).

Comments:

General

- The module uses indentation that varies all over the module, from 2 spaces to
5. Please fix the module to have consistent indentation.

- The module makes heavy use of groupings. They are great if they are being
used in multiple places. But I seem to see single usage of groupings, which
makes the model hard to read. Please collapse all groupings that are used only
once into the module.

Abstract:

It is best not to try to redefine terms, specially if they have already been
defined already in another RFC. Case in point, "state data". This term has been
defined in RFC6241, and it would be best to list it in the Terminology and
Notation section, as has been done with other definitions.

The following terms are defined in [RFC6241]:

   o  configuration data

   o  state data

Introduction:

Please update reference of YANG to RFC7950. These are YANG 1.1 modules after
all.

Section 5. The Design of the PCEP Data Model.

Thank you for first of all for creating a abridged version of the tree diagram.
What would really help to understand the design of the model would be to place
the full tree diagram at the end of the section, and move sections 5.3 to 5.7.
directly under 5.1. Scrolling through pages of the full diagram to get to the
design sections is painful to read.

Section 10. PCEP YANG Modules

- Please list all RFCs and I-D that are referenced in the model, so there is a
normative reference to them in the draft.

- Please expand the reference to different RFCs to include the title of the
RFC, and not just the number.

- The reference to tls-server and tls-client should be to
I-D.ietf-netconf-tls-client-server, as it is not an RFC as yet. Also, the
document refers to all other RFCs as RFC XXXX. What is the RFC editor supposed
to replace XXXX with? With the RFC number assigned to this draft?? I think you
want to refer to I-D that contain those modules.

- What is "PCEP common"? That term has not been defined anywhere in the
document, but is used in the YANG model.

- What is the 'identify pcep' for?

- Why is pcep-admin-status a enum and not a boolean? Since YANG nodes are
hierarchical, there should be no reason to repeat prefixes like 'admin-status'
in node names such as 'admin-status-up', both where it is defined and where it
is used (under admin-status).

- Where are the different operational status definitions defined? Can that RFC
be referenced? Same for Session state, Association Type, Objective Function.

- Could the YANG module use existing definitions? For example could the module
use ospf-area as defined in I-D.ietf-ospf-yang or use isis-area defined in the
ISIS YANG Module.

- Can the document use more descriptive names for features such as 'gco'.

- If the range of the timer is 1..65535, why does it need to be a uint32? Same
for the range of 0..255.

- RFC 5440 makes no reference to 'max-keep-alive-timer' or 'max-dead-timer'. If
they are max value, can they not be expressed as part of the range for
'keep-alive-timer' or 'dead-timer'? Same for 'min-keep-alive-timer' and
'min-dead-timer'.

- What is the default value for 'admin-status'?

- The grouping pce-scope seems to be defining a header with each of the leafs
as bits in the header. In that case, it would be better if this was defined as
a bits/bit field, rather than leafs that are of type uint8 and boolean. Same
for the grouping called 'capability'

- The description "LSP is PCE-initiated or not" is hardly a description for the
leaf 'enabled'. It might be more a description of the feature 'pce-initiated'.

- Could description "Valid at PCC" be improved upon?

- Most keys are defined as 'type binary'. Why is key-string defined as 'type
string' or 'type hex-string', and not 'type binary'? Is it possible to reuse
definitions from draft-ietf-netconf-crypto-types?

- I am not an expert in this protocol, but a lot of the nodes defined are
generated by the system. Yet, they are defined as rw. For example, the list
'path-keys' carries a description "The list of path-keys generated by the PCE".
If so, should this not be marked 'config false'. I would suggest authors take a
more concerted look and see what nodes are indeed rw and which ones are ro.
Other examples include 'req-id' and 'retrieved'.

- Can this error-message and description be reconciled?

                    error-message
                        "The Path-key should be retreived";
                    description
                        "When Path-Key has been retreived";

- It is great to see that extensive amount of statistics are required to be
implemented by the model. How many implementations actually support all these
statistics? What would happen if implementations support a small number of
these statistics? In other words, are all these statistics required to be
maintained/implemented?

- In addition, a lot of the statistics have when statements. Since these are
statistics maintained by the system, why the when statement? Does it mean that
even if the statistics are written by the system, they are not valid (for
reading) under certain scenarios. Or is it more likely that they are only
written when the role is ether of a 'pce' or 'pcc-and-pce', in which case
reading for other roles would return 0 values.