Gert Doering said: > On Tue, Oct 12, 2010 at 07:45:10PM +0200, Peter Rathlev wrote: > > I'm just guessing here, > > but I don't see why routed multicast traffic would need to have the L2 > > group bit set. > > Well, if you only ever have two routers in a subnet, it doesn't need to... > > But what if you have 20 routers in a subnet and want the multicast traffic to > be heard by only those 5 that are interested in it?
If those routers' interfaces are multicast enabled, an IGMP snooping switch will flood multicast traffic to them, regardless of interest in a particular group. http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00800b0871.shtml The switch listens to the following messages in order to detect router ports with IGMP snooping: · IGMP Membership query send to 01−00−5e−00−00−01 · PIMv1 hello send to 01−00−5e−00−00−02 · PIMv2 hello send to 01−00−5e−00−00−0d · DVMRP probes send to 01−00−5e−00−04 · MOSPF message send to 01−00−5e−00−05 or 06 By enabling IGMP snooping on a switch, all the above MAC entries are added to the show cam system command output of the snooping switch. Once a router port is detected, it is added to the port list of all GDAs in that VLAN. /chris _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
