From: Scott Morris (swm@emanon.com)
Date: Fri Nov 18 2005 - 02:12:40 GMT-3
No... Sparse mode has both shared and source trees. Source trees are a
virtue of how the multicasts flow, NOT specific to either sparse or dense.
Dense mode ONLY uses source-based trees, but has different mechanisms in HOW
that works.
So the pieces are kinda intertwined. In case you hadn't noticed in the
networking world, there very rarely is anything that is black and white
only! :)
Scott
-----Original Message-----
From: Schulz, Dave [mailto:DSchulz@dpsciences.com]
Sent: Thursday, November 17, 2005 3:59 PM
To: Scott Morris; Drew Whitaker; Cisco certification
Subject: RE: Preventing DM Fallback
Scott -
Are your last statement, are you saying that sparse mode has a dense mode as
well, and that it is able to fallback to dense mode? I thought that sparse
mode only will keep everything communicating through the RP (shared tree).
Do I have something backwards?
Dave Schulz,
Email: dschulz@dpsciences.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Scott Morris
Sent: Thursday, November 17, 2005 3:31 PM
To: 'Drew Whitaker'; 'Cisco certification'
Subject: RE: Preventing DM Fallback
Two different pieces actually....
DM Fallback refers to the process when you are running sparse-dense mode and
an RP (or shared tree) cannot be found for the group you are looking for,
then dense mode will work. So in that case, there never is a shared tree to
keep traffic on.
In sparse mode once you hit the RP and shared tree, the spt-threshold will
keep things on that tree instead of finding the better source tree someplace
along the way.
HTH,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Drew
Whitaker
Sent: Thursday, November 17, 2005 12:48 PM
To: Cisco certification
Subject: Preventing DM Fallback
This question for the group revolves around the idea of how to keep traffic
on a shared tree.
To disable dense mode fallback, I can type 'no ip dm-fallback' (thus keeping
traffic on a shared tree). Yet, in my reading, I have also come across the
command 'ip spim spt-threshold infinity' which, according to the Cisco
documentation, "causes all sources for the specified group to use the shared
tree." By using the shared tree, doesn't this also prevent DM fallback like
the 'no ip dm-fallback' command?
Also, in the "IP Multicasting Technology Overview" document (
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hi
mc_c
/
ch05/mcbcncpt.htm#wp1075142)
it says you can create a sink RP (RP of last resort) to ensure that no
groups (other than PIM v1 224.0.1.39 <http://224.0.1.39> and
224.0.1.40<http://224.0.1.40>groups) resort to a source tree. So wouldn't
this do it as well?
I am trying to understand the differences between these three methods.
Are
these three different methods to prevent multicast traffic from using a
source tree?
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