Subject: [MBONED] problem of multicast flooding discussion---thanks for recommendation from Brian Haberman

From: zhoudi <[email-masked]>
Date: Thu, 29 Jul 2010 12:55:45 +0800

Hi all,
   We'v found a problem in our network deployment.
   According to the recommendation from Brian Haberman, I bring 
this issue up here. Thanks.
   When there are one or more IGMP-Snooping switches between 
the multicast source and PIM DR, the multicast streams will
tranfer through these switches from source to DR, even if there
is no request from receivers. This often leads to waste of 
switches' cache and link bandwidth when the multicast streams 
are not actually required.
   The following is an example.
   
                ++++++++++
                + PIM DR +
                ++++++++++
                +         + 
       ++++++++++             +
       + switch +                  +
       ++++++++++                      +
        +     +                            +
      +        +                               +    
 ++++++++++    +++++++++++++++++++++++++++++       +++++++++++++++++++++++++++++     
 + source +    + other application client1 +       + other application client2 +
 ++++++++++    +++++++++++++++++++++++++++++       +++++++++++++++++++++++++++++

In such a common deployment, the client1 and client2 are communicating, such as 
some vedio application. 

If the switch is always forwarding streams which not requested, these streams will 
waste the cache of switch's port connecting PIM DR and the cache shared by all 
of the switch's ports. They will also waste the bandwidth of the switch's
port connecting PIM DR.

If replacing the switch with PIM router, these stream will not flood if not required.
But in the deployment where there are much sources, it is not acceptable to put an 
PIM Router beside each source. Because it will bring about deployment changing, such 
as ip address segment split, and cost increasing, such as equipment cost increasing
and ip address wasted. It will also bring about other problems, such as complicated 
network management.

If we can control the switch just forwarding the requested stream, and control the streams 
just stop at the exact switch, it will be perfect. 

I hope you are interested in solving this problem. Thanks.
                                   
Regards!
                                       Sincerely yours,Zhou Di