Re: [CCAMP] Thoughts on Flex-E YANG models

[Jiangyuanlong <[e-mail]>]

Hi Rob,

Thank you  a lot for your comments, they are very helpful.
Please see my further comments inline.

Cheers,
Yuanlong

From: CCAMP [mailto:[e-mail]] On Behalf Of Rob Wilton (rwilton)
Sent: Friday, November 22, 2019 11:01 PM
To: [e-mail]
Subject: [CCAMP] Thoughts on Flex-E YANG models

Hi,

I have some general thoughts on modelling Flex-E in YANG that may help the authors converge.  These comments mostly relate to what I would call the overall shape of the YANG model rather specific configuration (which I think can probably be sorted out once the shape has been agreed).


  1.  Flex-E groups should be identified by their group-number (both models seem to do this, but the group number seems to be optional in one model)
  2.  The configuration to identify the bonded phys should be under the flex-e group (both models do this).
[Jiang] Agreed to both.


  1.  In the flex-e group's bonded-phy interface configuration list, bonded-phy interface list entries could be keyed either by the bonded phy interface name, or the flex-e phy number.
     *   I would suggest that the bonded-phy interface name is the more meaningful identifier to clients.
[Jiang] Just to be clear, are your saying that the list of flexe-phy should be keyed by the interface name? I think in our model, current key "flexe-phy-if" is exactly the PHY interface name, as shown in RFC 8343:
"     typedef interface-ref {
       type leafref {
         path "/if:interfaces/if:interface/if:name";
"

     *   Either way, the entries should also indicate the binding to the bonded-phy interface (e.g. by an interface-ref - both models seem to do this).
  1.  The configuration required to define the client interfaces associated with a flex-e group should be under the flex-e group list entry, based on the assumption that that 16 bit client id must be unique within the group rather than across groups.
[Jiang] Totally agreed.


  1.  In the flex-e group's client interface configuration list, client interface list entries could be keyed either by the client interface name, or the client id.
     *   Again, I would suggest that using the client interface name is the more meaningful identifier for clients.
[Jiang] Earlier we already planned to use "flexe-client-if" as the key to flexe-client-list. Could this resolve your comment?


     *   Either way, the entries should also indicate the binding to the client interface (by interface-ref - both models seem to do this).
  1.  Client interfaces should be modelled as regular interfaces, and use the normal iftype for Ethernet interfaces, i.e. the dubiously named iftype:ethernetCsmacd.  Without using this type regular Ethernet YANG configuration (e.g. as defined in 802.3.2) won't work properly.
     *   I don't think that there should be flex-e specific configuration under the client interface itself, instead, the flex-e specific configuration should be defined as part of the group + client interfaces.
[Jiang] Agreed to bullet a). But I have some doubts whether we can use the normal iftype for Ethernet interfaces directly. As FlexE Client includes only a thin MAC layer, while PHY layer is decoupled into the FlexE PHY, FlexE client management should be simpler than the regular Ethernet YANG configuration, furthermore, it seems to me all the YANG models defined in 802.3 or 802.2 more or less include some PHY configuration which cannot be applied to a FlexE client. Nevertheless, we look forward to seeing more discussions on this topic.

But I think that the main issue to resolve is whether Flex-E group configuration is global or scoped to a FlexE group interface..  I can see pros and cons both ways:

  1.  Putting the configuration under an FlexE group interface seems like a slightly artificial construct.
  2.  However, this does mirror how LAG interfaces are represented (at least in our vendor model), and in some ways FlexE interfaces could be considered to be like an L1 LAG interface.  However, in the LAG case, the LAG interface can forward traffic, where as for FlexE groups, this would not be the case.
  3.  There is probably a natural binding between a FlexE group and the client interfaces that closely relates to the parent child relationship between an interface and sub-interface.  E.g. disabling a FlexE group should have the effect of disabling each FlexE client interface.
  4.  My overall feeling is that representing the FlexE groups as a type of interface seems like a reasonable configuration model.
[Jiang] Totally agreed.

Anyway, hopefully these comments are useful to help the two sets of authors converge towards a common model.  I have other suggestions on the specific models but would suggest solving the big picture issues first.
[Jiang] Very useful indeed, we look forward to your further suggestions on the models.

Regards,
Rob