Hello,

I have been selected as the Routing Directorate reviewer for this draft. The 
Routing Directorate seeks to review all routing or routing-related drafts as 
they pass through IETF last call and IESG review, and sometimes on special 
request. The purpose of the review is to provide assistance to the Routing ADs. 
For more information about the Routing Directorate, please see 
‚Äčhttp://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir

Although these comments are primarily for the use of the Routing ADs, it would 
be helpful if you could consider them along with any other IETF Last Call 
comments that you receive, and strive to resolve them through discussion or by 
updating the draft.

Document: draft-ietf-bfd-yang-09
Reviewer: Ravi Singh
Review Date: 02/09/2018
Intended Status: Proposed standard



Summary: there is more commonality of info in the new modules listed in 
sections 2.6-2.10 than there are differences. So, I think it would be 
worthwhile looking at sub-abstracting things to avoid repetitive fields 
individually listed in the modules of section 2.6-2.10.

Details:
I've reviewed the draft. Most sections look good.
My comments below pertain to 2.6 to 2.10.
Section 2 says "Since BFD is used for liveliness detection of various forwarding
   paths, there is no uniform key to identify a BFD session.  So the BFD
   data model is split in multiple YANG modules where each module
   corresponds to one type of forwarding path. "
That is ok. However, this is causing too much repetition of info across the 
multiple modules.
There appears to be scope for modularization to not repeat the individual 
fields in describing them in every module that uses them.
Instead sub-modules should be considered & listed in one section which just 
augment the newly created modules of this draft wherever currently used.

Eg.
Separate sub-modules could be considered for:
A.
        +--ro session-statistics
        |  +--ro session-count?              uint32
        |  +--ro session-up-count?           uint32
        |  +--ro session-down-count?         uint32
        |  +--ro session-admin-down-count?   uint32

B.
           +--rw source-addr                 inet:ip-address
           +--rw dest-addr                   inet:ip-address
           +--rw local-multiplier?           multiplier
           +--rw (interval-config-type)?
           |  +--:(tx-rx-intervals)
           |  |  +--rw desired-min-tx-interval?    uint32
           |  |  +--rw required-min-rx-interval?   uint32
           |  +--:(single-interval)
           |     +--rw min-interval?               uint32
           +--rw demand-enabled?             boolean {demand-mode}?
           +--rw admin-down?                 boolean
           +--rw authentication! {authentication}?
           |  +--rw key-chain?    kc:key-chain-ref
           |  +--rw meticulous?   Boolean

C.
              +--ro path-type?              identityref
              +--ro ip-encapsulation?       boolean
              +--ro local-discriminator?    discriminator
              +--ro remote-discriminator?   discriminator
              +--ro remote-multiplier?      multiplier
              +--ro demand-capability?      boolean {demand-mode}?
              +--ro source-port?            inet:port-number
              +--ro dest-port?              inet:port-number
              +--ro session-running
              |  +--ro session-index?                uint32
              |  +--ro local-state?                  state
              |  +--ro remote-state?                 state
              |  +--ro local-diagnostic?
              |  |       iana-bfd-types:diagnostic
              |  +--ro remote-diagnostic?
              |  |       iana-bfd-types:diagnostic
              |  +--ro remote-authenticated?         boolean
              |  +--ro remote-authentication-type?
              |  |       iana-bfd-types:auth-type {authentication}?
              |  +--ro detection-mode?               enumeration
              |  +--ro negotiated-tx-interval?       uint32
              |  +--ro negotiated-rx-interval?       uint32
              |  +--ro detection-time?               uint32
              |  +--ro echo-tx-interval-in-use?      uint32
              |          {echo-mode}?
              +--ro sesssion-statistics
                 +--ro create-time?            yang:date-and-time
                 +--ro last-down-time?         yang:date-and-time
                 +--ro last-up-time?           yang:date-and-time
                 +--ro down-count?             uint32
                 +--ro admin-down-count?       uint32
                 +--ro receive-packet-count?   uint64
                 +--ro send-packet-count?      uint64
                 +--ro receive-bad-packet?     uint64
                 +--ro send-failed-packet?     Uint64

D.
           +--rw (interval-config-type)?
           |  +--:(tx-rx-intervals)
           |  |  +--rw desired-min-tx-interval?    uint32
           |  |  +--rw required-min-rx-interval?   uint32
           |  +--:(single-interval)
           |     +--rw min-interval?               uint32


E.

              +--ro sesssion-statistics
              |  +--ro create-time?            yang:date-and-time
              |  +--ro last-down-time?         yang:date-and-time
              |  +--ro last-up-time?           yang:date-and-time
              |  +--ro down-count?             uint32
              |  +--ro admin-down-count?       uint32
              |  +--ro receive-packet-count?   uint64
              |  +--ro send-packet-count?      uint64
              |  +--ro receive-bad-packet?     uint64
              |  +--ro send-failed-packet?     uint64

F.       In notifications:
        +--ro local-discr?                 discriminator
        +--ro remote-discr?                discriminator
        +--ro new-state?                   state
        +--ro state-change-reason?         iana-bfd-types:diagnostic
        +--ro time-of-last-state-change?   yang:date-and-time
        +--ro dest-addr?                   inet:ip-address
        +--ro source-addr?                 inet:ip-address
        +--ro session-index?               uint32
        +--ro path-type?                   identityref

Separate sub-modules for the above could be used to enable cleaner 
abstractions. The same could augment the modules of sections 2.6-2.10.

Regards
Ravi

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