> https://arxiv.org/pdf/2211.09029.pdf
The paper is a useful high level review of what multicast promised and
why IP multicast has failed so far. As it says, "The takeaway here is
that the woes of previous multicast deployments can be overcome by
observing the lessons learned from those deployments..."
But its cheerful-charlie outlook about its "proposed new multicast
semantic" (which exact semantic, isn't clear) doesn't seem to address
any of three major issues in how today's Internet relates to IP
Multicast:
* Should the allocation of hundreds of millions of IPv4 addresses to
native multicast be reconsidered? Only a tiny fraction of them are
in use, while unicast is the clear success story of the Internet.
Unicast address demand continues to rise, while multicast demand is
invisibly small. IANA has never allocated roughly half of all
multicast addresses to anyone for any use (225-231/8 and
235-238/8). The vast bulk, of the tiny fraction that were
allocated, are for services now considered obsolete (all but LAN
use, e.g. for Neighbor Discovery or MDNS; and all but
Source-Specific Multicast, which is limited to 232/8).
* For end-users seeking access to nonlocal IP multicast, over the last
few decades, one issue at ISPs continued to get in the way. Large
backbone unicast routers could not reliably be used to forward
native multicast traffic, because enabling multicast on those
routers tended to make them crash (more often). When seeking
99.9999% uptime for the unicast traffic that pays all the bills,
and seeking low network debugging and support costs, having a
backbone router crash for even ten minutes a year from running a
niche service, caused ISPs too much trouble. So when multicast was
supported at all, it tended to be supported on side-machines that
were not in the main pipelines of the ISP, were not as highly
capable as the mainline routers, and required custom tunnel
configuration from each end-user -- a non-starter for mass market
use.
* And with few or no ISPs supporting multicast by default, no end-user
applications that tried to use it ever caught on. So there was
very little demand encouraging other ISPs to enable multicast.
The paper does not seem to address any of those issues.
John Gilmore
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