Re: [Idr] RFC5065 - Section 5.3

Danny McPherson <> Tue, 08 July 2008 16:16 UTC

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Subject: Re: [Idr] RFC5065 - Section 5.3
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On Jul 8, 2008, at 8:25 AM, David Freedman wrote:

> Thanks, I do indeed understand but believe it makes it harder now to
> convince vendors to "enhance" implementations now that there is an
> explicit "SHOULD NOT"

It says "SHOULD NOT", not "MUST NOT".  This was done
for interoperability reasons.

Just a reminder, RFC 2119:
2. MUST NOT This phrase, or the phrase "SHALL NOT", mean that the  
definition is an absolute prohibition of the specification.
4. SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that  
there may exist valid reasons in particular circumstances when the  
particular behavior is acceptable or even useful, but the full  
implications should be understood and the case carefully weighed  
before implementing any behavior described with this label.
Given BGP's deployment footprint and the path selection
criteria of existing routers, and the probability of introducing
routing stability with changes of this sort, this text still seems
prudent, IMO.

That said, given that even route reflection CLUSTER_LIST
lengths are considered in path selection, I do consider this
to be a reasonable request, convince your vendor(s) to do it,
the specification certainly doesn't prohibit it.


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