Re: UDLR: Comments on draft-ietf-udlr-experiments-00

> ---
> Section  4.5.1. DR Election
> 
> The use of the word "listener", should perhaps be "source" ???

"listener" is the intended word.

The DR has two tasks:
 - send register messages to the RP
 - originate Join/Prune messages to the upstream router toward the
   RP/source if a listener exists on the network segment.

In my understanding of Scenario D, there should be no multicast listener
on the UDL segment, correct?

The paragraph about DR election states that "if a multicast listener
exists ...", which is not the case for the Scenario D.
The last sentence of the paragraph is:
   In the Scenario 5, DR election result is not important as all UDL
   nodes are multicast routers.
There is a typo there: "Scenario 5" should be "Scenario D".
I guess I should change the text into "if a multicast listener exists as
in the Scenario A and B..." to make it clear.

> 
> ----
> PIM Join Override?
> 
> Finally, does anyone have experience of a large PIM-routed network
> based on UDLR links?

We do not have a large UDLR environment.
I experimented with cisco 2621 routers running PIM-SM and found out that
the cisco I used did not suppress Join message. 
Does anybody have similar experiences like this?


> 
> Do we get cases where there are an implosion of Join-Overide messages
> being issued by receiver multicast routers when one router sends a 
> prune?

Let me make an illustration.
Suppose that the unidirectional link contains 1000 PIM-SM routers and
there are 10 multicast streams flowing on the link. Furthermore, suppose
that each router joins all streams.
If a router no longer needs to forward a stream, it sends a Prune
message toward the upstream router. The other routers have to send
overriding Join message to keep the stream flowing on the link.
If the overriding Join suppression is disabled, then there would be 998
overriding Join messages flowing on the link. If at almost the same time
there is a Prune message for each stream, there would be 9980 overriding
Join messages flowing on the link.

This is the worst-case scenario for 1000 routers and 10 streams.

If overriding Join suppression is enabled, the question is about the suppression
effectiveness.
This is an implementation issue, mainly regarding the probability
distribution function of the random timer used to generate overriding
Join messages. (research issue)

I think we can show (and solve) the cases for large flat networks using
simulation .


-- 
Achmad Husni Thamrin <[email protected]>