Subject: PIM-SM source aggregation

From: Sudhir Cheruathur <[email-masked]>
Date: Mon, 20 Sep 1999 10:57:51 -0700

Hi ,

I have a question on source aggregation in PIM-SM.

Consider the following network.

    R1----------------------R2------s1,s2
     |                         |
     |                         |
    R4----------------------R3
     |
    G

  (in case the above figure is unreadable)
  R1 is connected to R2 and R4. 
  R2 is connected to R3 and R1 
  R3 is connected to R2 and R4
  R4 is connected to R1 and R3

  Let R1 be the RP.
 
  Let sources 1.1.1.1(s1) and 1.1.1.2(s2) be connected 
  to R2 on another interface.

  A host on R4 wants to recv packets to group G.

  When source S1 starts to send packets to G, At
R2, (S,G) is created where is S is (1.1.1.0,G).
  
   When source S2 starts to send packets to G. The above
   (1.1.1.0,G) is used to send packets to the RP.

Now R4 initiates SPT towards S1. However the (S,G)
created here is (1.1.1.1,G),

After the SPT tree (via R3) is built, we have the following states

At R4  (1.1.1.1,G) upstream R3.
At R3  (1.1.1.1,G) upstream R2.
At R2  (1.1.1.0,G) upstream local interface.

Because of these states traffic from S2 also starts following 
down the SPT tree (towards R3). But will get dropped at R3.

I am sure I am missing something. 

Or is it required that all routers use  fully qualified source
addresses for (S,G) ?  The J/P packets contain the netmask
so intermediate routers can have same (S,G) as the 
one who initiates the joins. But what happens at the 
sender's/receiver's end ?

Thanks,

Regds
Sudhir C