From: Scott Morris (swm@emanon.com)
Date: Fri Jan 02 2004 - 23:50:19 GMT-3
The default of the command is not to always use the shared tree.. The
default is to have no effect on operation. If you use the 'infinity'
parameter with the command, that's how you get to always use the shared
tree!
Scott
-----Original Message-----
From: Dmitry Volkov [mailto:dmitry.volkov@rogers.com]
Sent: Friday, January 02, 2004 9:28 PM
To: 'Scott Morris'; 'Yasser Aly'
Cc: ccielab@groupstudy.com
Subject: RE: Role of Rendezvouz point in multicast
Just to add :
command "ip pim spt-threshold" can trigger whether to switch so SPT:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_command_summ
ary_chapter09186a008007fd31.html#xtocid62
default: "Causes all sources for the specified group to use the shared
tree."
Dmitry
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Scott Morris
> Sent: Friday, January 02, 2004 9:07 PM
> To: 'Yasser Aly'; ccielab@groupstudy.com
> Subject: RE: Role of Rendezvouz point in multicast
>
>
> The RP is the "know it all" of the multicast network. It prevents
> every router from needing to maintain state for every single multicast
> group that exists. In our lab networks, we generally could care less
> about this, but in real life, this could get ugly!
>
> Yes, an edge multicast router may decide to not go with the RP. But
> only AFTER it joins the shared tree and starts to get multicast
> traffic. Only then does it learn where the source actually is, and
> can examine its routing table to determine whether it really is on the
> shortest path tree (SPT) or not. If not, then it will create a source
> distribution tree directly to the source.
>
> So while yes it's true, it's not always the case. Just depends on
> where source and receivers are located compared to the RP.
>
> So specifically to your questions:
>
> 1. Only for the *,G tree and MAYBE for the S,G tree.
> 2. Only after seeing multicast traffic and IF it determines that the
> source is closer to itself than the RP is.
>
> HTH,
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
> CISSP, JNCIS, et al.
> IPExpert CCIE Program Manager
> IPExpert Sr. Technical Instructor
> swm@emanon.com/smorris@ipexpert.net
> http://www.ipexpert.net
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of Yasser Aly
> Sent: Monday, December 29, 2003 6:39 PM
> To: ccielab@groupstudy.com
> Subject: Role of Rendezvouz point in multicast
>
> Dear All,
>
> I am confused about the role of RP in multicast sparse-mode. I
> thought that a shared distribution tree will be created where sources
> register themselves with the RP and receivers send request to RP.
>
> However after reading the following lines from a PDF speaking about
> configuring RP, I got confused.
> Kindly have a look at the lines below and let me hear your feedback.
>
> My questions mainly are:
> 1) Will multicast traffic pass by the PR all the time on its way from
> source to receiver or not ?
>
> 2) Is it true that after the first hop router of the receiver learns
> about the source, it will send a join message directly to the source,
> creating a source-based distribution tree ??
>
> Your thoughts are highly appreciated
>
> ---------
>
> An RP acts as the meeting place for sources and receivers of multicast
> data.
>
> In a PIM-SM network,
> sources must send their traffic to the RP. This traffic is then
> forwarded to receivers down a shared distribution tree. By default,
> when the first hop router of the receiver learns about the source, it
> will send a join message directly to the source, creating a
> source-based distribution tree from the source to the receiver. This
> source tree does not include the RP unless the RP is located within
> the shortest path between the source and receiver.
> In most cases, the placement of the RP in the network is not a complex
> decision. By default, the RP is needed only to start new sessions with
> sources and receivers. Consequently, the RP experiences little
> overhead from traffic flow or processing. In PIM-SM version 2, the RP
> requires less processing than in PIM-SM version 1 because sources must
> only periodically register with the RP to create state.
> -----------------------
>
> Regards,
> Yasser
>
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