Re: Why MSDP?

[Ali Boudani <aboudani@irisa.fr>]

I think I didnt understand well the SA message.

In unicast (using BGP), a source can send messages without disturbing the BGP ,
so why isnt the case in MBGP??
and if we imagine that we are using PIM-SM shared tree, then it is the same as
unicast ?? (in some way).

what am I missing here?
thanx


>         Not sure about the history of this thread, but here's some
>         of the history.
>
>         First, we looked at putting SAs into BGP. I wanted to
>         do this as a first thought since the MBGP/MSDP split
>         effectively splits the control plane. However, this
>         turned out to be a less than optimal solution for several
>         reasons, not the least of which included:
>
>         (i).    State
>
>                 The reason MSDP is periodic and not incremental
>                 (and originally non-caching) is that we were tryin
>                 to avoid explosion of (S,G) state. I guess we're
>                 not so worried about that (c.f. SSM). In addition,
>                 we had to somehow (attempt to) solve the bursty
>                 source problem.
>
>         (ii).   BGP Stability
>
>                 I don't really want to argue that the dynamic nature
>                 of SA advertisements is going to help the stability
>                 of BGP (that is, of the global routing system). Neither
>                 do you, I would guess.
>
>         (iii).  Deployment
>
>                 Because of (i). and (ii). above, SAs in BGP would have been
>                 impossible to deploy (who would want to deploy a
>                 version of BGP that carried SAs? MBGP with SAFI \in {1,2}
>                 was hard enough).
>
>
>         There were a few other things, but these were the main concerns.
>         BTW, what we were doing was attempting to find a way to free
>         providers from having to co-locate their RPs on a dense-mode
>         exchange point (i.e., get (S,G) state from outside their domain onto
>         their RPs so their customers could join those groups, w/o sharing
>         RPs). That was the (lost in the mist of history) design goal.
>
>         Dave
>
>
> According to Ali Boudani:
> >
> > > One reason: the timescales for change of active source indications are
> > > much different than BGP was designed to carry.  BGP wants to carry
> > > data that doesn't change very often, e.g. see route dampening.  Sources
> > > can come and go at an arbitrary rate, so the rate of change of the
> > > information is potentially much higher.
> >
> > can you specifie more,
> > why should the timescales for change active source indications are much
> > different.???
> >
> >