Subject: [pim] PIM assert function

From: Kumar P <[email-masked]>
Date: Sun, 3 Oct 2004 23:28:43 -0700 (PDT)

Hello All,
 
I am new to PIM, want someboby clear my following doubt.
 
It is mentioned in the PIM draft that assert condition is likely to happen in multi-access environment where in there are more than one upstream routers present and have different opinion on reaching RP or Source, hence generate Join according and end up in receiving multiple streams of same data.
 
Draft also mentions that there should only one forwarder in such environments, which is nothing but DR in this case. So DR in this case is responsible for generating Join after it receives igmp join or pim join from its downstream terminals. My doubt is when there is single DR(hence forwarder) on this multi-access media, how does the other routers send join towards RP or Source when ther are not responsible for the same.
 
When a router doesn't send Join message also doesn't forward the multicast streams. Please clarify this.
 
TIA,
Kumar

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From: Prashant Jhingran <[email-masked]>
Date: Tue, 05 Oct 2004 12:03:55 +0800

Hello Kumar,

Welcome to the group.

Let me briefly explain you the following points about a DR:

1. The concept of DR and DR election is important in case of PIM-SM and
not PIM-DM.

2. You are correct when you say "So DR in this case is responsible for
generating Join after it receives igmp join" but incorrect when you say
"...or pim join from its downstream terminals".
-- DR election is necessary for electing a DR on a LAN, a router which
is responsible for initiating  PIM trees (PIM-SM) as a result of IGMP
reports. Hence in PIM-SM a DR starts acting as a forwarder on the LAN.
However, the DR may loose an Assert election and therefore the winner
may become the forwarder on the LAN.
--In case of PIM-DM, its the assert mechanism which decides the
forwarder on the LAN and DR election has nothing to do with the
forwarder in DM.

3. The concept of DR is once again is of no use when it comes to
exchange of join/prune messages between the PIM routers. 
--If you think over this point then you may come to a conclusion that
Assert mechanism is required due to the above reason and also that
Assert mechanism is an efficient way of deciding  the forwarder on the
LAN.

Hope this may clear your doubts.

Regards,
Prashant Jhingran

Huawei Technologies 
Beijing, China
Ph# 00-86-10-82882837  (O)  

"You see, all the problems in the world are created by those who want
'perfection.' " -- Sri Sri Ravi Shankar  www.artofliving.org  

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Kumar P
Sent: Monday, October 04, 2004 2:29 PM
To: [email-masked]
Subject: [pim] PIM assert function

Hello All,

It is mentioned in the PIM draft that assert condition is likely to
happen in multi-access environment where in there are more than one
upstream routers present and have different opinion on reaching RP or
Source, hence generate Join according and end up in receiving multiple
streams of same data.

Draft also mentions that there should only one forwarder in such
environments, which is nothing but DR in this case. So DR in this case
is responsible for generating Join after it receives igmp join or pim
join from its downstream terminals. My doubt is when there is single
DR(hence forwarder) on this multi-access media, how does the other
routers send join towards RP or Source when ther are not responsible for
the same.

When a router doesn't send Join message also doesn't forward the
multicast streams. Please clarify this.

TIA,
Kumar

---

From: Kumar P <[email-masked]>
Date: Mon, 4 Oct 2004 23:10:19 -0700 (PDT)

Hello Prashant, 
 
Please see my inline response...

Prashant Jhingran <[email-masked]> wrote:

Hello Kumar,

Welcome to the group.

>> OK agreed, in this case downstream routers put it's immediate upstream neighbour's address in join message, hence nexthop might not be the DR here. But in "Multi-access Transit LANs" (draft-ietf-pim-sm-v2-new-09.txt), how does PIM join state is maintained in other router(even if they have routing inconsistency) when the downstream router sends the PIM join message to a particular upstream router? and resulting two seperate join messages towards their respective upstream neighbours?. My understanding is that, since join message is sent to a particular upstream router(even though its destination address is Multicast address), or atleast downstream router is saying that "this PIM join message is supposed to be processed by the router which I have included in this message as -upstream neighbor address". When such is the situation, why does the other routers which are present in the same "Multi-access Transit LAN" process this message to create Join state and propagate join to!
 wards its
 final destination?

>> Here again similar situation, when DR is supposed to take care of sending PIM join, why does the other router sending Join and pulling the multicast data? If the other router(other than DR) doesn't initiate the the PIM join, then there wouldn't be Assert I guess.

>> Sorry, I am still unable to understand. 

Regards,
Prashant Jhingran

Huawei Technologies 
Beijing, China

-----Original Message-----

Hello All,

TIA,
Kumar