Metro Ethernet Multicast Support

Holmes,David A dholmes at mwdh2o.com
Tue Nov 4 14:13:35 CST 2008


The Metro Ethernet Forum (MEF) MEF10-1 ELAN multipoint-to-multipoint
specification says that multicast packets must be replicated out all
ports in the ELAN, except the ingress port. Some carriers have taken
this literally and built a virtual ELAN service emulating a 1990's style
hub in which all multicast packets are replicated out all ports
regardless of the L3 multicast routing protocol in use. In the case of
PIM sparse mode real physical Ethernet switches use IGMP snooping to
construct a directed path through the switch fabric, so that a given
established multicast stream is forwarded just like a directed unicast
connection with mac/port table entries establishing a single path
through the L2 fabric, and no flooding is done. Some carriers flood
directed multicast traffic out all ELAN ports even though a single path
should be taken. In networks with a large number of directed multicast
streams, flooding out all ports uses unnecessary bandwidth, sometimes
rendering a 10 Mb port useless due to oversubscription caused by this
unnecessary flooding.

Can anyone suggest a carrier MEF ELAN multipoint-to-multipoint service
that does not flood established directed PIM sparse mode streams?    



More information about the NANOG mailing list