From: Bob Sinclair (bob@bobsinclair.net)
Date: Mon Feb 27 2006 - 16:12:27 GMT-3
BIDIR is a strange beast:
Unlike Dense mode, Bidir does not flood to all PIM neighbors, only up the
shortest path tree to the RP. If there are no clients who want traffic, then
Dense will prune back. BIDIR only prunes back to the RP, then the RP drop it.
Traffic continues to be forwarded from the source to the RP as long as it is
active. Receivers join much like regular sparse-mode: explicit joins toward
the RP.
BIDIR is a lot like spanning-tree: think of RPF interface as root port;
think of DF interface as designated port. Basic rule then is if a port is not
RPF or DF, then it cannot forward for the group. In fact, BIDIR is similar
to Core Based Tree, which Radia Perlman had a hand in developing.
Good for many-to-many multicast because it minimizes state.
Try labbing it up and doing some "debug ip mpacket". Just enable globally
(ip pim bidir-enable) and add the "bidir" keyword to your RP statements.
Bob Sinclair
CCIE #10427, CCSI 30427
www.netmasterclass.net
----- Original Message -----
From: CCIEin2006
To: Bob Sinclair
Cc: ccielab@groupstudy.com
Sent: Monday, February 27, 2006 1:24 PM
Subject: Re: Difference between Bidirectional PIM and PIM Sparse Mode
Hi Bob,
Since the first hop routers forward the traffic whether its wanted or not,
isn't that like dense mode?
Do receivers still send joins to the RP?
What does the RP do with the traffic if there are no receivers - send a
prune?
Thanks!
On 2/27/06, Bob Sinclair <bob@bobsinclair.net> wrote:
>
> Bidirectional PIM Differs from Sparse mode in at least these ways:
>
> Bidir does not maintain any (S,G) state. Only (*,G) state. This is what
> makes it scalable for many-to-may multicast.
>
> Bidir does not do PIM registration. First-hop routers do not register
> traffic with the RP. First hop routers, forward traffic for active
groups
> toward the RP, whether anyone wants the traffic or not, as long as the
group
> is active.
>
> Since there is no PIM registration, the RP does not actually have to be a
> reachable address, only a reachable network that acts as a root.
>
> Here is a link with more info:
>
>
>
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configurati
on
_guide_chapter09186a00800ca796.html
>
>
> HTH,
>
> Bob Sinclair
> CCIE #10427, CCSI 30427
> www.netmasterclass.net
>
>
> ----- Original Message -----
> *From:* CCIEin2006 <ciscocciein2006@gmail.com>
> *To:* ccielab@groupstudy.com
> *Sent:* Monday, February 27, 2006 11:28 AM
> *Subject:* Difference between Bidirectional PIM and PIM Sparse Mode
>
>
> Hello group,
>
> I am not very clear on the differences between Bidirectional PIM and PIM
> Sparse Mode. Both use the RP and switchover to shortest path tree after
> the
> first packet is received, correct?
>
> How do they differ exactly?
>
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