Re: [mpls] I-D Action: draft-ietf-mpls-sfl-framework-01.txt

[Balaji venkat Venkataswami <[e-mail]>]

Hi Stewart,

I get it now. In order to avoid midway changes to the ECMP path once the
flow has begun
the draft advises to use the SFL label always from PW or VPN creation time
to the end of the
flow to get it to take one ECMP path throughout the lifetime of the flow
consistently. Replacing the SFL
with the original application label may cause it to take a different path
midway.

The rest is very clear.

Thank you for your kind explanation.

thanks and regards,
balaji venkat

On Mon, Jan 29, 2018 at 10:08 PM, Stewart Bryant <[e-mail]>
wrote:

>
>
> On 29/01/2018 14:50, Balaji venkat Venkataswami wrote:
>
> Hi Authors,
>
>
> In the current version of the draft, this follows in section 5.
>
>
>
>
>    The introduction to an SFL to an existing flow may cause that flow to
>    take a different path through the network under conditions of Equal
>    Cost Multipath (ECMP).  This is turn may invalidate the certain use
>
>    of the SFL such as performance measurement applications.  Where this
>    is a problem there are two solutions worthy of consideration:
>
>    1.  The operator can elect to always run with the SFL in place in the
>        MPLS label stack.
>
>
> What this is saying is that you could set up monitoring at for example PW
> or VPN
> creation and always run with that extra label. This is not ideal but the
> ECMP issue goes away. In other words always run with the SFL in place.
>
>
>
>
>    2.  The operator can elect to use [RFC6790] Entropy Labels in a
>        network that fully supports this type of ECMP.  If this approach
>        is adopted, the intervening MPLS network MUST NOT load balance on
>        any packet field other than the entropy label.  Note that this is
>        stricter than the text in Section 4.2 of [RFC6790].  In networks
> Bryant, et al.           Expires August 2, 2018                 [Page 7]Internet-Draft                   MPLS FI                    January 2018
>
>        in which the ECMP decision is independent of both the value of
>        any other label in the label stack, and the MPLS payload, the
>        path of the flow with the SFL will be congruent with the path
>        without the SFL.
>
>
>
> This is an alternative to point 1. Use the EL system (always) and require
> a strict implementation
> of it in which the only packet characteristic taken into account when
> selecting the ECMP path
> is the value of the EL.
>
> The text seems clear, but if you have any changes in mind please let me
> know.
>
> Best Regards
>
> - Stewart
>
> Question ?
>
> You dont seem to be considering the consequences of point 1 in the
> explanation given.
> Or are you trying to say that if point 1 is what is followed, the ECMP
> decision should be
> independent of the SFL label in place and the MPLS payload, so that the
> path of the
> flow with the SFL in place will be congruent with the path without the SFL
> ?
>
> Are you specifying something in point 2 that also applies to point 1 ?
>
> Please clarify.
>
> thanks and regards,
> balaji venkat
>
>
>