Stefano, Chris and all,
I have to admit that I am completely confused:
        - to the best of my understanding, Chris has asked whether a policy 
that puts a limit on max. number of ECMP next hops is not compatible with the 
Strict SPF algorithm
        - Stefano says that "Yes, this policy is a good example when Strict SPF 
algorithm can be advertised".

What do I miss?

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-----Original Message-----
From: spring [] On Behalf Of Stefano Previdi 
Sent: Monday, September 19, 2016 12:43 PM
To: Chris Bowers <>
Subject: Re: [spring] meaning of "Strict Shortest Path" algorithm in 

> On Sep 14, 2016, at 7:06 PM, Chris Bowers <> wrote:
> The current text in draft-ietf-spring-segment-routing-09 regarding the 
> "Strict Shortest Path" algorithm reads as follows.
>    o  "Strict Shortest Path": This algorithm mandates that the packet is
>       forwarded according to ECMP-aware SPF algorithm and instruct any
>       router in the path to ignore any possible local policy overriding
>       SPF decision.  The SID advertised with "Strict Shortest Path"
>       algorithm ensures that the path the packet is going to take is the
>       expected, and not altered, SPF path.
> One example of a local policy that overrides the ECMP-aware SPF 
> algorithm decision is a limit on the number of ECMP next-hops.  The 
> text above implies that if a router places any limit on the number of 
> ECMP forwarding next-hops then it would be wrong for it to advertise the 
> “Strict Shortest Path” algorithm capability.
> Is this the intended interpretation?

well, yes. Your example is a good one for the “strict-SPF” behavior.


> If not, what is the intended interpretation?
> Thanks,
> Chris
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