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

[Stewart Bryant <[e-mail]>]

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