All things related to multicast

[John Kristoff <>]

Bear with me here if I"m not making much sense... I seem to work on
multicast issues every 6 months and doing so tends to make my brain hurt
every time I dive back in.

On Tue, 30 Nov 2004 13:15:44 -0800 (PST)

 wrote:

> YES, if you change the priority of the candidate DR so that it becomes the 
> elected DR, then the magic of IGMP/PIM will move the state. Then you can 
> do what you like with the other router as it is no longer in the path.

I see in the latest draft spec, it's recommended that implementations
keep local membership state even if they are not DR.  This appears to
be the case on my Cisco boxes.  So given that... when the new DR is
elected, it should immediately issue the appropriate joins while the
old DR router removes it's OILs (and IIFs in my case as long as the new
DR is also the active HSRP interface).  If my interpretation is correct
I suspect there may be a very small window of packet loss as the path
changes.

> Setting the PIM hello interval will help reduce the convergence times upon 
> an unscheduled failure event.

That may be something I can investigate.  A previous contributor's post
regarding the use of a tracking interface for HSRP and unicast traffic
was interesting also.  I think I'd prefer to use something like BFD or
just hello timers for handling unicast routing decisions rather than
messing with OSPF weights, but that was a useful observation also.  I
wonder if it would be useful to consider BFD between PIM peer interfaces.

In any case I'm not sure I want to implement all the custom tweaks, 
since a few seconds of downtime along with a simpler config may just
be easier.  Though as we try to maintain as near perfect uptime as
possible this is all useful stuff to at least understand better.

Thanks for all the responses.

John