[Bier] Shepherd’s review of draft-ietf-bier-bgp-ls-bier-ext-07

[Gyan Mishra <[e-mail]>]

Dear Authors,

Thank you for a well-written succinct document.

I have a few  comments and questions on the use of BGP-LS extension and why
it is necessary for BIER and what gap that exists that is being addressed
by this extension.

What is broken today?

The abstract and introduction describes how BIER works which anyone reading
the draft can read normative references RFC 8279 and RFC 8296.

The last sentence says the following:

This document specifies extensions the BGP Link-state address-family
in order to advertise BIER information.


The last sentence in the introductionstates the following:


In order to satisfy the need for applications that require topological
visibility across one area or Autonomou

System (AS).  This document specifiesextensions to the BGP Link-state
address-family in order to advertise BIER-specific.  An external
component
(e.g., a controller) then can collect BIER information in the "northbound"

direction within the BIER domain.


Section 3 goes on to describe how this new BGP-LS extension for BIER will
be able to gather the BIER specific topology information and send
Northbound to an external controller which will then build rebuild a
topological graph of the BIER domain or multiple domains for multicast
“applications” that won’t work for without this extension.

I think in the draft it is important to note the gap that exists today
without this draft and clearly what is broken that is being fixed by the
draft.

That should be spelled out clearly in the Introduction as well as stated
briefly in the abstract.

Inter-AS BIER trees can be built without a controller and this BGP-LS
extension, similar to today inter-as MVPN mLDP PE P2MP TE stateful
segmented or end to end LSP trees.

I think we need to expand more on the application visibility and what
applications I am guessing ASM, SSM trees over BIER inter-as, but I still
don’t understand the gap as what won’t work with multicast applications
today without this BGP-LS extension for BIER.

Please help me understand.

Also could BIER BGP-LS extension also be used for BIER inter-as
provisioning of stateless tree?

  So possibly be used for instantiation of all inter-as stateless trees
based on the topological graph.  As the BIER trees are stateless in a way
you could pre build all X-PMSI trees set the BFR bitmask for all egress PEs
ahead of time provision inter-as from BFIR ingress domain to BFER egress
domain.

There maybe other use cases or reasons for BGP-LS usage by BIER but I think
provisioning could be one of them.

Once I have received feedback on the comments I will compile the Feedback
and complete the Shepherds write-up.

Kind Regards


Gyan
-- 

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *



*M 301 502-134713101 Columbia Pike *Silver Spring, MD