Re: Dumb question about routing headers

For the multicast data plane to build the multicast path during the RPF
check for source or shared tree bust be the same interface as the path
through which the unicast destination was learned for the source for ASM or
SSM source tree or RP for ASM shared tree.  If you had previous segments
that were unicast and then all of sudden at a multicast segment thrown in
it would be a recursion issue there the unicast RPF interface has to be set
uRIB present and then multicast mRIB would use the same interface for its
RPF check based on pim being enabled uRIB path.

That scenario would not work.  All segments have to be unicast segments.  I
believe this question came up on PGM draft WGLC in regards to RFC 8200.  I
think the address type on PGM was lose and not descriptive as it should be
but from a technical multicast perspective it’s not possible to interleave
multicast with unicast segments as RPF check would fail.

Gyan

On Sun, May 24, 2020 at 5:23 PM Nick Hilliard <nick@foobar.org> wrote:

> Brian E Carpenter wrote on 24/05/2020 22:05:
> > Is a routing header whose final destination is a multicast address,
> > but whose previous segments are all unicast, valid?
>
> .... or whose intermediate destinations are multicast addresses?
>
> https://twitter.com/brenankeller/status/1068615953989087232
>
> Nick
>
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*Gyan Mishra*

*Network Solutions A**rchitect *

*M 301 502-134713101 Columbia Pike *Silver Spring, MD