From: Brian McGahan (brian@cyscoexpert.com)
Date: Sun Dec 15 2002 - 16:39:07 GMT-3
Rehan,
Auto-RP is based on two main components, candidate RPs and RP
mapping agents. Candidate RPs send periodic multicast messages to a
reserved well-known group 224.0.1.39. The RP mapping agents join this
group, 224.0.1.39, and determine which RP will service which particular
group (an RP to group mapping). After this is determined, the RP
mapping agent advertises these RP mappings via another well-known group
address, 224.0.1.40.
The problem with this design, however, is that all routers
running PIM Sparse mode must first have an RP mapping for any group they
wish to join. Since the Auto-RP announce and discovery groups are
multicast, these client routers would first have to know who the RP is
before they could find who the RP is. This is like a paradox, or an
error in recursion. To solve this problem, you have the option to run
the PIM domain in sparse-dense mode.
Remember that the fundamental difference between PIM sparse and
PIM dense:
PIM Sparse = explicit join
PIM Dense = explicit leave
In sparse-dense mode, any groups for which you do not have an RP
mapping will be in dense mode. This means that all routers will belong
to the groups 224.0.1.39 and 224.0.1.40. Therefore, they can
automatically listen for the Auto-RP messages without having to define
an RP beforehand.
Your assumptions are therefore correct, and some possible
solutions to this problem are as follows:
1. All routers are directly connected to the mapping agent
2. Run PIM in sparse-dense mode
3. Define a static RP for the groups 224.0.1.39 and 224.0.1.40
4. Join all PIM interfaces to the groups 224.0.1.39 and 224.0.1.40
For more information on auto-rp:
ftp://ftpeng.cisco.com/ftp/ipmulticast/autorp.html
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
Voice: 847.674.3392
Fax: 847.674.2625
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> rehan u nedaria
> Sent: Sunday, December 15, 2002 10:01 AM
> To: ccielab@groupstudy.com
> Subject: Mulicast Basic
>
> Hi All
> May be a silly question but i m bit confuse on it.I was
> reading jeff doyle vploume 11 page number 559 for multicasting.
>
> There is example where it is been explained when to use
> sparse/dense mode.This is if the mapping agent is not directly
> connected to the C-rp and other routes in that case u need to use
> sparse/dense mode.
>
> Here r the following queries.
>
> 1)All the routers in my network need to be connected to the
> mapping agent directly including the C-rp.
>
> 2)If this is not the case then i have to use sparse dense mode
> where the router is not directly connected.
>
>
> Please help me to find out the correct logic behind this.
>
> Regards
> Rehan
> .
.
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