Re: hi

Let's talk about Multicast (MCAST)!

Multicast Distribution Trees - This is the root of the shared tree.

PIM Neighbors - PIM is the language of MCAST we care about for the CCIE Lab.
So let's not waste much time.

Routing Protocols - We need a path (RPF Check)

Neighbors - We need to know where to send or receive a MACST packet from.

Source - We need to know where the packet came from.

There it is folks... Black and White.

Who: As in "Who is the source?"

Where: As is "Where is the neighbor?"

RPF Check: As in "Where is the source and how do I know which PIM enabled
interface to send the MCAST packet to in order to get there?"

Let's talk about PIM Mode:

1. Any Source Multicast (ASM)

- PIM-SM
- Supports both shared and source trees.

2. Source-Specific Multicast (SSM)

- Single Source Multicast (Hint: We are being specific here).
- Supports only Source Trees (No need for RP's, RP Failover, etc.)

3. Bi-directional PIM (Bidir-PIM

- Supports only shared trees.

Here's a quick and simple process.

Computer A wants to subcribe or join a mulicast feed.

So...

Computer A makes an assumption that Router A: knows the RP, has the RP in
its RIB via an IGP with Router B, and has a neighbor relationship with
Router B. It is further assumed that Router B shares similar assumptions for
each router in the path to the RP (which might actually be on any router in
the path).

So I guess we have some questions...

If router A send a PIM (*,G) "Join" out what is really happening anyway?

1. Sending a PIM 224.0.0.13 to all PIM Routers - Kewl.

- Note there are like 5 options here...

- 0 = Hello (Multicast to ALL PIM ROUTERS)
- 1 = Register (Unicast to RP)
- 2 = Register Stop (Unicast to source of Register packet)
- 3 = Join/Prune (Multicast to ALL PIM ROUTERS)
- 4 = Bootstrap (Multicast to ALL PIM ROUTERS)
- 5 = Assert (Multicast to ALL PIM ROUTERS)

- Note we also send the version of the PIM too...

2. Wondering about the IP of the RP?

3. Wondering about the IP of Router B (the PIM neighbor who is in the path
or tree to the RP).

What is the Destination IP of the PIM we sent out in item number 1?

- 224.0.0.13

What are we expecting in return?

- The IP of the RP

Where are we expecting to receive it from in general?

- From a neighbor

which neighbor in this little example?

- Router B

Why would we expect to receive the RP's IP from this neighbor?

- Because it is the closest router that is also a shared PIM neighoor and
knows of the shared tree to the RP.

Now let's introduce Router C. Router C is on the same shared segment as
Router A and Router B. Router C also has an interface that is in the same
segment as Router A and Router B. Furthermore, that interface is also PIM
enabled.

So...

If the destination IP address of the Join is 224.0.0.13 and 224.0.0.13 is
"All PIM Routers" (In our case Router B and Router C)...

Then the question becomes "How do we determine which router will act on this
Join and not say... both routers?"

Hmmm...

Give it a minute to sink in...

Remember we know that the upstream neighbor is the target of the message...
right?

Ok - Let me see if I can finish writing up this basic example and clear some
clouds up.

The idea is to take the concept and expound on it.

We watched Narbik do this from a CLI perspective quite wonderfully and
masterfully.

I've been spending a little time trying to ensure I understand what is
actually happening first and foremost... then I'll take the example(s) and
break them down from a CLI perspective with various show or debug commands
when/if/as needed.

The idea is to:

1. Understand the concept. In this case we need to fully understand that a
Multicast Router needs a few things to work:

- Be enabled on the router (Hey -meet me half way - ip muticast-routing or
ip mulitcast-routing ditributed)
- Be enabled on the interface in the correct mode (Gotta have the correct
operational mode- Sparse, Sparse-Dense, or Dense)
- Have a neighor that is PIM enable (Neighbor Check)
- Have a route (usually via IGP for example) to the RP (RPF Check)
- Know where the source is located (IP Address)

2. Once we understand the concept and the components then we need to know
the basic configuration commands.

3. Then we need to know the basic verification exams.

---------------------------------------------------------
At this point, I'd say we are still at a CCNP level
----------------------------------------------------------

4. Then we need to know those special commands use to help MCAST overcome
hurdles as they might be presented in the Lab.

5. We also need to ensure we understand all the show and debug output at an
expert's level.

6. Items 1-5 will allow us to correctly configure and troubleshoot IP
Multicast in the CCIE Lab both effeciently and effectively - resulting in
100% of the Mlticast Points that may or may not be available in any given
lab.

Now let's introduce Router C. Router C is on the same shared segment as
Router A and Router B. Router C also has an interface that is in the same
segment as Router A and Router B. Furthermore, that interface is also PIM
enabled.

So...

If the destination IP address of the Join is 224.0.0.13 and 224.0.0.13 is
"All PIM Routers" (In our case Router B and Router C)...

Then the question becomes "How do we determine which router will act on this
Join and not say... both routers?"

Hmmm...

Give it a minute to sink in...

Remember we know that the upstream neighbor is the target of the message...
right?

Let's see...

Where was I...

Oh yes, how does Router A know whether to use Router B or Router C as the
next hop upstream router if both are PIM enabled neighbors?

Hmm...

Well for this we need a little more information. Like the IP Address of
each. In this case let's say that Router A is 172.16.123.1, Router B is
172.16.123.2, and router C is 172.16.123.3....

Now which is selected?

Think about it.

Hmm....

Ok - I'll be back later with the correct answer

In this case they are directly connected. So the IP Address would be the tie
breaker and the hisghest will be Router A's choice for the next hop.

Router C is the winner.

On Sun, Aug 2, 2009 at 11:42 PM, sameer khan <skkingpk11253006_at_gmail.com>wrote:

> Hi
> Confuse about the active source in multicasting
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
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Received on Mon Aug 03 2009 - 00:05:02 ART