All things related to multicast

[Dan Pritts <>]

I'm not about to suggest that we drop support for wide-area IPv4 multicast. There are legitimate uses still being made of it, even though there aren't any in evidence on our network this Monday morning. I'm really beginning to wonder whether IPv6 multicast has a future, though. It seems to me that we're now seeing the other side of the adoption curve for wide-area multicast in general, and as a result we aren't going to have even the low volume of interesting applications for IPv6 multicast that drove the original adoption for IPv4.

I won't even go so far as to suggest that we 'early adopters' turn off interdomain IPv6 multicast, although nobody would notice. But if anyone is actively using interdomain IPv4 multicast, they really should get to work moving their application over to IPv6 before the tiny number of networks who support it decide that it's just another source of complication, bugs and potential security holes, and dump it.

I project-managed the network build for 12 Internet2 member meetings between 2006 and 2012.  Some of these were easier than others to make happen, but one consistent problem was getting multicast working.  Even in DC, where MAX just turned on and off the same config year after year, I'm pretty sure it got crufty and broke at least once during that period.

We never really saw a lot of application adoption.  We had a few of the same folks every year, fighting the good fight, but never any critical mass.

When I arrived in the R&E networking world in 2002, multicast was still viewed as an advanced technology.  It was clear to me, early on, that it was really difficult to make it work properly, but there was at least the hope that deployment of IGMPv3 would be the magic bullet. 

When I left Internet2 this past , we had not turned on IGMPv3 on our office LANs, because none of the applications worked with it (to be clear, our equipment was capable, and we'd tested it).  We were still running MSDP and having to bug Merit or MAX occasionally when something broke. 

I never felt comfortable saying so while I was an Internet2 employee, but inter-domain multicast is dead.  For the record, there was no explicit gag rule.  The general feeling was that if members wanted it, we should do it, and it surely wasn't my place to tell the membership otherwise. 

Now I'm a member, so I say, shoot it in the head, and put it out of our misery.

Disable IPv6 multicast immediately.  No one will notice. 
 
Phase out inter-domain IPv4 multicast over the next year or two. A few people will have to change their applications.

Most importantly...spend everyone's engineering effort on something more useful.

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Dan Pritts
ICPSR Computing & Network Services
University of Michigan
+1 (734)615-7362