Re: RFC 5771 - Global Multicast Addresses

[Niels Bakker]

* bran...@brandonsjames.com (Brandon James) [Mon 05 Aug 2019, 17:17 CEST]:
As a young network engineer (no historic perspective) and only SMB 
and enterprise experience. It seems like the intention was to allow 
these to be publicly routed, but it would be a nightmare to 
implement so it never was.


Multicast was never popular with operators because it had the 
potential to create a lot of state across every router in a network, 
as well as lead to uncontrolled explosions of traffic, especially in 
network designs that relied on virtual circuits for significant 
portions of last-mile infrastructure.


Some of these problems were addressed with SSM, IP DSLAMs, and having 
consumer connection speeds be significantly faster than what a Full HD 
video stream requires, but given that major network providers already 
don't have the in-house clue to implement IPv6, multicast will be very 
low priority.



-- Niels.

--
"It's amazing what people will do to get their name on the internet, 
which is odd, because all you really need is a Blogspot account."

-- roy edroso, alicublog.blogspot.com

RFC 5771 - Global Multicast Addresses

[Brandon James]

Good Evening,

I'm looking for some insight into the usage of a few of the blocks defined in 
RFC 5771 (and IPv6 Multicast Addressing as described in RFC 4291 and 7346) , 
specifically regarding their use on the public internet. I know multicast isn't 
routed  on the public internet. However, it appears that this may be due to 
operational issues and concerns or that it was simply never implemented. The 
specific blocks I'm looking at are (as defined in RFC 5771 Section 3-10:

Internetwork Control Block - 224.0.1.0/24
> Addresses in the Internetwork Control Block are used for protocol control 
> traffic that MAY be forwarded through the Internet

AD-HOC Blocks (I, II, and III) - 224.0.2.0 - 224.0.255.255, 224.3.0.0 - 
224.4.255.255, and 233.252.0.0 - 233.255.255.255
> These addresses MAY be globally routed

GLOP Block (233/8) - Global routing is never mentioned in RFC 5771, but given 
the context and the use of ASNs, I'm not sure if the intention was for these to 
be publicly routable or to simply to guarantee that the address would be unique 
within your AS (are large telcos and webscale companies exhausting 239.0.0.0/8?)

IPv6 Multicast Addresses with scope 0xE - The RFC doesn't really go into detail 
on how these would be used.

As a young network engineer (no historic perspective) and only SMB and 
enterprise experience. It seems like the intention was to allow these to be 
publicly routed, but it would be a nightmare to implement so it never was.

You'd probably require PIM Sparse Mode (we can't flood traffic to the entire 
internet), RPs would need to be advertised somehow (maybe BSR could be 
implemented with RP advertisements coming from the providers edge?). RPF would 
be a constant process and shortest path trees would change constantly.

That's all without mentioning 224.0.1.0/24 is tiny and the AD-HOC and GLOP 
blocks aren't exactly huge given the size of the internet.

I'd love to hear what others have to say about this, maybe get some historic 
perspective and thoughts on whether or not any of this will change as IPv6 
adoption increases. I'd also love to see any guidance on actually implementing 
multicast on the internet from IANA or the IETF (or guidance that says that it 
should not or can not be done) as I wasn't able to find any.

Regards,

Brandon