Re: You asked about multicast scope

On 3/29/2012 3:38 AM, Kerry Lynn wrote:
> On Thu, Mar 29, 2012 at 12:02 PM, Iljitsch van Beijnum
> <iljitsch@muada.com <mailto:iljitsch@muada.com>> wrote:
>
>     On 28 Mar 2012, at 12:08 , Fred Baker wrote:
>
>      >> I haven't read the spec yet, but isn't PCP supposed to work in
>     the service provider run NAT64/CGN case, too? In that case, the
>     multicasts need to escape out of the site or even organization to
>     reach the service provider at least in the SOHO case. So this would
>     be a scope just shy of global, maybe a new "service provider" scope?
>
>      > I personally rarely use "zero configuration" and "service
>     provider" in the same sentence...
>
>     Am I understanding you correctly when I take that to mean that the
>     admin (value 4) scope is appropriate because then the people running
>     the multicast routing can determine exactly how far these packets
>     travel?
>
>     That makes sense, but there is one potential issue, that I think
>     some people who are well-steeped in IPv6 multicast should look at:
>     in this situation, the scope value 4 may need wider distribution
>     than side-wide, which is scope 5. I can't find any documentation on

IMO you cannot do that. The higher scope value, the wider distribution.
If you have scopes X and Y where X < Y, then the distribution of X
should be a subset (can be the same) of the distribution of Y.

There are implementations making such assumptions.

>     whether that's ok or not between sessions right now, but I'm
>     reluctant to assume that a lower scope value can have wider
>     distribution than a higher one without having a spec that explicitly
>     says so or hearing from some implementers.
>
> Correct me if I'm wrong, but isn't Admin Scoped multicast defined on a per-
> port, per-application basis?  That would suggest that some multicast group
> addresses can (selectively) be forwarded through the CER uplink to the ISP.

There is nothing magical with scope 4. It is wider than link-local, and
you need to configure routers to limit the distribution according to
your policy.

Stig

> -K-
>
>     Iljitsch
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