Re: [Idr] [draft-ietf-idr-segment-routing-te-policy] Error handling for Explicit NULL Label Policy Sub-TLV

[Przemyslaw Krol <[e-mail]>]

Hi Nandan,

I personally agree with your proposal for handling multiple ENLP sub-TLV
(1). It's clear and consistent with other similar cases

In terms of ENLP = 0 || >=5 (2), my concern regarding 2b (fallback to
static) is that there may be multiple instances of BGP policy (different
advertisers) with the same or lower preference and valid ENLP values.
Failing back to static would basically skip those BGP policies and "bypass"
policy selection. I suspect it's undesirable. For this reason, treating it
as reserved (2a) sounds to me like a better option. Unless you really meant
ignoring offending policy and moving to the next one (which can be static
or BGP, depending on the selection algo), but regardless, 2a) seems safer
and less disruptive in the future (if/when we need ENLP >=5 ).


thanks,
pk

On Thu, May 16, 2019 at 12:42 AM Nandan Saha <[e-mail]> wrote:

> Hi folks,
>  There error handling for the ENLP sub-TLV isn't defined in
> draft-ietf-idr-segment-routing-te-policy-05 [1].
>
> There are 2 things that need to be clarified:-
>
> 1. The behavior when ENLP sub-TLV occurs more than once:
>   For this, my preference is to add text like we have for policy
> priority sub-TLV [2] (and some other sub-TLVs), mandating only one
> occurrence and treat-as-withdraw when present more than once.
>
> 2. Behavior when ENLP value is either 0 or >= 5.
>   The only meaningful/legal values defined now are 1-4. My preference is to
> 2a: mark other values as reserved for future use. (We could mark them
> illegal but that'll rule out trying to extended them if ever needed)
> and
> 2.b: Upon receipt ENLP = 0 || >=5 the headend call fall back to local
> policy. (If we go down the route of marking 0 || >= 5 as illegal, we
> can do TAW)
>
> Please let me know what you think, and if this seems reasonable.
>
> [1] -
> https://tools.ietf.org/html/draft-ietf-idr-segment-routing-te-policy-05#section-2.4.4
> [2] -
> https://tools.ietf.org/html/draft-ietf-idr-segment-routing-te-policy-05#section-2.4.5
>
> Thanks,
> Nandan
>


-- 
Przemyslaw "PK" Krol |  Strategic Network Engineer ing | [e-mail]