From: Dmitry Volkov (dmitry.volkov@rogers.com)
Date: Fri Jan 02 2004 - 23:28:27 GMT-3
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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