Re: [pim] Replacing unicast BSMs with multicast

[Stig Venaas <stig.venaas at uninett.no>]

John Zwiebel wrote:
> I would guess that in a service provider environment, the
> use of a static-RP is much preferred.  When you say anycast-RP
>
> I'm also guessing that it probably an MSDP anycast system vs
> a PIM anycast.
>
> Within an enterprise, I'll bet there is more auto-rp deployed than
> either static-RP or BSR (but that depends on that enterprise having
> cisco routers only of course).

My impression would be static-RP for server provider and BSR/auto-rp 
more for enterprises, but I haven't seen that many different ones.
> Since we don't often get a look into the same customer network,
> our subjective analysis of which RP distribution method is most used
> will probably be very skewed, so much so that I'm not sure it is useful
> argue about which vendor has what method most broadly deployed.

Right. I don't think it's all that useful to compare how many there are 
either. Even if BSR is less used than static RP (which is the case for 
networks I'm most familiar with), the BSR usage is I think significant.
> At this point of mcast deployment, it is my opinion -- based on nothing
> in particular -- that very few, if any, networks have more than one RP
> address (where anycast-rp is "one RP") or have RPs that support  different
> group ranges. (certainly in the ISP case this is true)

Several academic networks (which is what I'm most familiar with), you 
might call them ISPs, provide a global RP as a service. Universities, 
colleges etc then can choose to run their own RP only for local groups 
(some admin scope ranges and a few other groups as well), while using 
the provider's RP for global groups. This is a fairly straightforward 
way of deploying PIM-SM without any need for MSDP.

It's not so easy to use BSR in such a setting. Perhaps one could 
statically configure the global RP and use BSR internally on the campus. 
Perhaps one could use scoped BSR, but I would generally recommend static 
myself.

> However, we are on the verge of video making the transition to IP and
> I predict this means more RPs with a rapid convergence on SSM to avoid
> setting up any shared-trees, especially in the ISP environment.
>
> And in the enterprise, IFF sparse-mode survives, there will be a lot
> of RPs serving a variety of group ranges.

I suppose for non-SSM, you could make it simpler and a bit more SSM-like 
by having RPs for special purposes and selected groups, where the RP is 
the source at the DR and the RPT and SPT are the same...

> Or, with more bidir, there
> will be the need to set up RPs for many temporary groups, and since the
> RP in bidir doesn't actually -do- anything, there -might- be a smart
> way of determining the receivers in the group and allocating an RP
> address in the center of those receivers rather than trying to
> set it up in advance.

Which also reminds me of embedded-RP. This is not so different from 
trying to do embedded-RP for IPv6 with bidir.

> If I'm correct, the ability of the BSR to quickly distribute RP  
> information
> will become very useful.  (This also assumes the withering of Dense-mode
> since the BSR protocol doesn't have an easy way of identifying a 'hole'
> to be reserved for dense groups, auto-RP does, but 'who cares'? ;-)

I suppose one draw-back of BSR vs auto-RP is that BSR uses its own 
flooding algorithm instead of a standard one :)

Stig

> On Apr 26, 2006, at 9:37 AM, Leonard Giuliano wrote:
>
> > On Wed, 26 Apr 2006, Cao Wei wrote:
> >
> > -) Hi, John
> > -)    I can not give the accurate number that how many PIM routers  
> > are running in the network.
> > -) But as I know,  BSR/BSMs is more popular static RP. A colleague  
> > has years experience
> > -) on network deployment  agree with me.
> > -)
> >
> > I would respectfully beg to differ.  Static Anycast RP has been the  
> > choice
> > of nearly every deployment I have seen.  In fact, I see absolutely  no 
> > use
> > for BSR, and would love to see it deprecated.  Unless you prefer more
> > complexity and less functionality, Static Anycast RP has all the  
> > benefits
> > and lacks some of the disadvantages of BSR.
> >
> > The only place I have seen BSR deployed is where certain equipment
> > actually supported only BSR and somehow didn't allow static RP  (even 
> > when
> > the RP was some other box).
>
>
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