Re: Auto-RP sparse mode

Guys,

In a nutshell, Cisco consider the sparse-dense mode to make Auto-RP work.
Why? because before having a functioning multicast network you needed to
send and receive multicast traffic of 224.0.0.39/40. What a mess. Remember
the egg!

It acted just like a pain killer at that time, and some issues were seen
when in WAN-based networks their RP(s) went down. Without a valid RP,
sparse-dense falls back to "dense only" and ruins low bandwidth ISDN, DDR
etc. links.

(Some) Solution(s)?

1- Don't use Auto-RP. Go to 4.
2- Use it with the Listener feature (new IOS needed - sometimes possible)
3- Disable the whole fallback thing and stop multicast.
4- Use some other Mcast technologies like SSM or BSR

Your question is "what is number 3?" - it means "hey I do comprehend that in
case of RP failure if I use this command I am not going to have any
Multicast traffic, but I prefer not to have multicast since the chatty dense
mode is a more serious threat to my shaky infrastructure".

Just think about it; you have a massive network across the EU with 1000
offices, both RP's just died do you want to saturate your WAN links with
multicast traffic and keep taking support calls about network/app slowness
until you fix the problem or you just prefer to shut off multicast until it
get's fixed up?

My answer depends on the importance of multicast traffic and whom I work
for, if it's a stock exchange application in Manhattan I'd take the rap and
keep the multicast traffic going but it it's ESPN video broadcasting to see
how Spain wins the cup I'll go for a temp shut off.

HTH
Kambiz Agahian

CCIE Instructor/Consultant
M.Eng Telecom, CCIE# 25341, CCSI# 33326, MCSE, MCSA

On Tue, Aug 10, 2010 at 2:27 PM, karim jamali <karim.jamali_at_gmail.com>wrote:

> Hello Experts,
>
> The whole story put short is that Auto-RP depends on two basic functions:
> 1.Candidate-RP which sends its information to the mapping agent using
> 224.0.1.39
> 2.Mapping agent which distributes the results to the other router using
> 224.0.1.40
> 3. Most important fact is that 224.0.1.39/224.0.1.40 are dense mode
> groups.
> 4. A sparse mode interface can't forward a dense mode group out the
> interface, thus the Auto-RP groups will be blocked, and we will not be able
> to have a converged domain, i.e. all the routers agreeing on who the RP for
> a particular group is.
> 5. Cisco came up with the 1st solution which was using sparse-dense-mode,
> this allows the two Auto-RP groups to be passed, and to reach a converged
> domain. A group which has an RP is treated as sparse/a group with no RP is
> treated as dense. The ip pim dm-fallback allows a group which lost its RP
> to
> still continue to function/run as a dense mode group.
> 6. The last solution/permanent one is using sparse-mode and auto-rp
> listener. Well eventhough the syntax "ip pim auto-rp listener" has nothing
> to do with what the command does, it is saying eventhough these 2 groups
> 224.0.1.39/224.0.1.40 and although I am only running a sparse mode
> interface, I will allow these advertisements ONLY to go through.
>
> HTH,
>
> Best Regards,
>
> On Tue, Aug 10, 2010 at 10:52 PM, Rohit Ghodke <rohit.nw_at_gmail.com> wrote:
>
> > Hello,
> >
> > Correct me if Im wrong about any of this
> >
> > The ip pim dm fallback feature is for sparse-dense mode and allows dense
> > mode flooding for groups without an RP.
> >
> > On Tue, Aug 10, 2010 at 9:24 AM, GAURAV MADAN <gauravmadan1177_at_gmail.com
> > >wrote:
> >
> > > For the groups that RP is found : Sparse mode .
> > > For the groups where RP is not found : Flooded like dense mode .
> > >
> > > On Tue, Aug 10, 2010 at 6:51 PM, masroor ali <masror.ali_at_gmail.com>
> > wrote:
> > > > Hi,
> > > >
> > > > In auto-RP sparse-dense mode, why the traffic is sent through Dense??
> > > > unable to understand the auto-RP listener and ip-dm fallback feature,
> > > >
> > > >
> > > > --
> > > > Regards,
> > > > Masroor Ali
> > > >
> > > >
> > > > Blogs and organic groups at http://www.ccie.net
> > > >
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>
> --
> KJ
>
>
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Received on Tue Aug 10 2010 - 18:58:11 ART