richard dumoulin wrote: > > Dear all, > > I am still struggling in understanding the differences and > needs and meanings of Multicast designated routers and IGMP > queriers. > Can anyone help ?
IGMP lets a workstation tell a local router that the router needs to send a multicast stream to the LAN where the workstation resides. IGMP works in the control plane. It's somewhat analagous to ARP which is used by a workstation and its local router to learn how to reach each other via MAC addresses. It works in that same local control plane. In addition, you need routing, however. Just like in unicast routing, multicast designated routers must run multicast routing protocols to learn the best path to multicast receivers. There's various options for multicast routing including MOSPF, if you're using OSPF, DVMRP, and PIM. PIM has caught on as the de facto standard. Multicast routing protocols, like unicast routing protocols, work in the management plane. These planes that I mention are very helpful for understanding issues like the one you bring up. They come from the international telecommunications world. A telephony example helps understand it. When you pick up your telephone handset, the local switch in the Central Office gives you dial tone. That's in the control plane, like IGMP. To actually make and receive phone calls, however, complicated protocols like SS7, etc., run in the management plane to learn paths (and other info in the case of SS7). On data networks, unicast and multicast routing protocols have the job of learning the best paths. The third plane, the user plane, carries the actual data (or phone call in the case of telephony). Does that help? Does it address your concerns? It's usually the first concern people have when learning multicast. Priscilla > > Regards. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=51461&t=51458 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
