All things related to multicast

[Bruce Curtis <>]

On Jan 16, 2008, at 3:13 PM, Stig Venaas wrote:

> Dan Pritts wrote:
> > On Sat, Jan 12, 2008 at 01:21:04PM -0500, Alan Crosswell wrote:
> > > - What do we do about multicast over WiFi networks?  We are  
> > > looking at
> > >   systems that distribute entertainment content to students in their
> > >   dorm rooms, and, as we all know, students don't use wired networks
> > >   anymore.  What are the issues with various vendors' WiFi  
> > > products and
> > >   multicast snooping, pruning, rate limiting, etc.?
> > I tried this back in the 802.11b days with a mix of apple airports
> > and cisco 350s.  Even when i rate-limited multicast to 512kbps the
> > network was unusable.
> > I believe this was because 802.11a/b/g all drop down to the speed of
> > the slowest client associated to the AP when sending broadcasts, and
> > they made no attempt to do anything more intelligent with multicast.
> > the slowest data rate in the 802.11b spec is 1Mbps; I guess the  
> > 512k of
> > multicast i sent plus all the 802.11 MAC layer stuff was just too  
> > much.
> > if i recall correctly, 802.11 is pretty chatty to prevent stations  
> > from
> > stepping on one another.
> > Looks like the lowest rate in 802.11g is 6Mbps (assuming you  
> > disable b compatibility).  Probably not good enough for IPTV, i  
> > assume you'd need
> > to support several 2-4Mbps streams?
>
> Right. I wish it was possible to configure the minimal rate  
> somehow, and
> just say that any clients below that speed won't get it.
>
> I have the impression that somehow both multicast and IPv6 is
> problematic with some of the controller based solutions. I have  
> however
> not tried to study this myself. It would be great to hear what
> experiences people have in such environments.
>
> Stig

  We have enabled IPv6 on our Cisco controller based solution which  
interestingly required enabling multicast (since IPv6 uses multicast  
for Neighbor Discovery).  But we haven't tested advanced features  
such as rate-limiting IPv6.  But the basic IPv6 connectivity seems to  
work OK.

  We have seen bugs in multicast requiring more throughput like  
watching a stream though.

> > I should be able to attend the BoF.
> > danno
> > --
> > Dan Pritts, System Administrator
> > Internet2
> > office: +1-734-352-4953 | mobile: +1-734-834-7224


---
Bruce Curtis                         

Certified NetAnalyst II                701-231-8527
North Dakota State University