Subject: bi-dir PIM-SM: need to extend the assert mechanism

From: Ardas Cilingiroglu <[email-masked]>
Date: Fri, 19 Mar 1999 15:53:30 -0500 (EST)

I believe assert mechanism needs to be extended to assert 
downstream oifs on the same subnet as the upstream traffic.
Example follows:
 
              (*,G)            (*,G)
               RT1              RT3 
                |                |
               1|oif            3|oif
           -----+----------------+------
               2|iif            4|iif
                |                |
               RT2              RT4
              (*,G)            (*,G)

Assume all routers have a (*,G) entry, with RT1 being the 
upstream for RT2 and RT3 being the upstream for RT4.

When data is sent from a source S downstream to RT4, the
following set of events will happen:

  - data will arrive at RT4, and forwarded upstream on RT3 
    and downstream on RT2
  - same data will also be received on RT1 as part of the
    RPT distribution, and forwarded downstream on RT2 and RT4

Note that receivers down to RT2 and RT4 have received data twice.
A solution to this would be to assert oif 1 on RT1 by creating 
an (S,G)RPT entry.

thanks,
Ardas

---

From: Dino Farinacci <[email-masked]>
Date: Mon, 22 Mar 1999 07:41:07 -0800 (PST)

>>                1|oif            3|oif

    This won't happen. Both RT2 and RT4 will use the *same* upstream
    router basd on unicast routing. That is, either RT1 *or* RT3 will have
    the LAN in the olist (the other will not). That same router will forward 
    packets upstream to the RP.

Dino