Multicast Acquisition Protocols
There are two accepted types multicast acquisition protocols, alleged close and dispersed mode. Close approach agency that every multicast router receives every multicast packet unless and until it absolutely says that it doesn't appetite it. As we will altercate shortly, this applies to anniversary accumulation and anniversary interface separately. Dispersed mode, on the added hand, agency (loosely) that no router will accept a multicast accumulation unless it absolutely requests it. It is important to agenda that end devices, whether multicast servers or accumulation members, are absolutely blind of which approach their arrangement uses, or alike which multicast acquisition protocol. Indeed it is accessible to run a arrangement area the routers use a aggregate of these modes.
There are abounding examples of dense-mode protocols, such as Agreement Absolute Multicast-Dense Approach (PIM-DM), Distance Vector Multicast Acquisition Agreement (DVMRP), and Multicast Open Shortest Path Aboriginal (MOSPF). There are beneath sparse-mode protocols, with the best examples actuality Agreement Absolute MulticastSparse Approach (PIM-SM) and Core-Based Copse (CBT).
Not all of these protocols are accessible in Cisco routers. Like best vendors, Cisco accouterments PIM-DM and PIM-SM as able-bodied as MBGP. But Cisco does not apparatus MOSPF or CBT, and has a bound adaptation of DVMRP.
There are two added accepted categories of multicast acquisition protocols: agreement abased and agreement independent. The aberration has to do with the alternation with an basal acquisition protocol, and not with the adeptness to handle nonIP multicast traffic. All of the multicast protocols mentioned in this book are specific to IP multicast communications.
For example, MOSPF is protocol-dependent because it relies on OSPF and uses a appropriate OSPF LSA blazon to backpack advice about multicast routing. PIM and CBT, on the added hand, both use the multicast cartage itself, forth with the accepted unicast IP acquisition table and IGMP requests to body the multicast forwarding trees. Back they don't affliction how the router got its unicast IP acquisition table, they are alleged agreement independent.
For the arrangement engineer, these distinctions are absolutely important, back they affect flexibility, reliability, and arrangement performance. In general, if you accept a ample network, decidedly with bandwidth accountable WAN links, and the multicast sources and destinations can be added or beneath anywhere through your network, you should use a agreement absolute dispersed approach multicast acquisition protocol. If you're not abiding if this absolutely describes your network, it is about safer and easier to angular in this administration anyway.
The PIM protocols, and, in particular, PIM-SM, are about the best choices for implementing new multicast networks. In the accomplished there were problems with interoperability in multi-vendor networks, as altered router manufacturers implemented altered sets of multicast acquisition protocols. Back DVMRP was the aboriginal broadly implemented multicast acquisition protocol, the aphorism of deride acclimated to be that DVMRP was the best way to acquiesce advice amid groups of routers from altered vendors. However, a quick analysis of protocols accurate by above router vendors shows that about all of them now abutment PIM as able-bodied as DVMRP.