Subject: [Anima] GRASP multicast frequency

From: Brian E Carpenter <[email-masked]>
Date: Thu, 30 Mar 2017 07:08:29 +1300

One more thing from our tests this week.

We noticed when testing at busy times that link-local multicasts
were often dropped. We would see quite long gaps when discovery
and flooding simply did not occur. Suspecting that the wireless
network was limiting the rate of multicasts, I cheated for a
few minutes by sending multicasts 10 times more frequently,
and the gaps in performance vanished.

According to the NOC:
>  > Do the access points throttle the rate of IPv6 link-local multicasts?
>  Yes, we do MLD snooping on our wireless LAN controllers to prevent
>  multicast storms over the air. The MLD timeout and MLD query interval are
>  set to 60 seconds and 20 seconds, respectively.

So, on a busy network the effect of that is apparently to incent
a protocol like GRASP to increase its rate of LL multicasts to grab a
sufficient share of capacity.

Since we need the autonomic mechanisms to work well in times of
overload, this effect needs to be understood by implementors.

Regards
   Brian