Multicast and switches

Jean-Francois Mezei jfmezei_nanog at
Thu Dec 18 22:55:08 UTC 2014

In Bell Canada territory, on the copper, Bell uses 2 VLANs , 35 for
data, and I think 36 for IPTV service.

Multicast is of course enabled on VLAN 36 and on the IPTV aggregation
network back up to the video servers which is separate from the data

VLAN 35  is set to aggregate to the BRAS router somewhere upstream.
Currently, independent ISP traffic is separated at the BRAS and PPPoE
packets reach the ISP premises from BRAS via L2TP links.

Multicast cannot be handled by this service.

One of the proposals is to have ISPs connect at the CO directly into the
switch feeding the DSLAMs. ISPs think that they can then do multicast
without needing Bell's intervention.

My concern is with ISP traffic still needing to pass through at least
Bell 2 switches and the DSLAMs before reaching the end user.

If ISPs pass through this equipment via a differerent VLAN (lets call it
37), would it just be a simple deal of telling those switches and VLAN
to "enable multicast"  on that VLAN, or would it require careful
configurations to enable specific multicast IPs etc ?

Would switches and DSLAMs handle multicast on separate VLANs as totally
separate realms so that one need not worry about the other using same
multicast IPs ? Or is this untested territory since there nobody ever
tried this ?

(I assume that on the Australian NBN, NBNCo would assign separate IP
ranges to different IPtv providers and traffic would be handled as a
single multicast system).

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