Re: [Idr] Review of draft-abraitis-bgp-version-capability-07

[John Scudder <[e-mail]>]

(Individual contributor hat on, one of the chairs will follow up tomorrow.)

Hi Adrian,

A couple of points —

>> On Aug 20, 2020, at 9:29 AM, RFC ISE (Adrian Farrel) <[e-mail]> wrote:
> ...
>>> [?] Was the use of draft-ietf-idr-ext-opt-param considered?
>> 
>> Author to respond, but I believe that while this is available, it is seen
>> as "unlikely to become an RFC any time soon". That would mean that either
>> the author had to fold it in to this document (which I would think makes
>> it absolutely IDR work) or sit with a normative reference for ever.

Actually it’s passed WGLC and the only hurdle remaining is for me (or someone) to clean up the implementation report before it’s shipped off for publication. This is fairly high on my to-do list. In my view it’s actually *likely* to become an RFC in the near future.

> ...
>>> [major] The length to be considered is not 255 octets of Capabilities,
>> but of Optional Parameters -- take a look at rfc4271/§4.2.
> 
> Oh, this is a splendid point!
> And here we have the issue that even modest constraint on the length of
> the Capabilities may cause us to run out of space for other Optional
> Parameters.
> 
> IANA helpfully shows us that there are not many optional parameters
> defined
> (https://urldefense.com/v3/__https://www.iana.org/assignments/bgp-parameters/bgp-parameters.xhtml*bgp-parameters-11__;Iw!!NEt6yMaO-gk!TSP1xJLtCVzr536UQhjnXHW6dt7cLC-OL8cHzqOIX5Mj8anMiLqgJVjms6HwiQ$ )
> so this problem is not rampant, but it raises two questions for the
> authors:
> 1. Why a capability code and not an optional parameter?
>  (I suspect the registry assignment rules may have a lot to do with
>  this!)
> 2. How do you stop the version capability crowding out other optional
>  parameters?

It’s my view that there will likely never be another Optional Parameter defined. The property they have of causing a session reset if not supported is unpleasant for operational purposes. With 20/20 hindsight, we probably should have just bit the bullet and deprecated Optional Parameters, redefining them as something more like Capabilities, but instead we carefully fit Capabilities into the pre-existing Optional Parameters, and we’re stuck with it now. For practical purposes, Capabilities are BGP’s optional parameter mechanism, and the RFC 4271 Optional Parameters field is vestigial. 

I trust that answers your question (1), and I think (2) has already been covered both above and elsewhere in the thread.

—John