about the area and then passes it on to the backbone (Area 0) routers in a
summary LSA. The same is done for the multicast topology. The ABR sum-
marizes which multicast groups are active and which groups have sources
within the area. This information is then sent to the backbone routers.
of the area. Each area has an ABR that performs these two functions within
an OSPF network.
same as an ABR but must be able to communicate with non-OSPF speaking
devices. Multicast group information and data is forwarded and received by
the Multicast Autonomous Border Router (MASBR). Because MOSPF runs
natively within OSPF, there must be a method or protocol by which the mul-
ticast information can be taken from MOSPF and communicated to the
external AS. Historically, DVRMP has provided this bridge.
Now we will dedicate some time to learning how it is used in conjunction
with the other multicast routing protocols. Although PIM dense mode (PIM
DM) maintains several functions, the ones that will be discussed here are
flooding, pruning, and grafting.
classless subnet masking and uses it when the router is running an IP classless
unicast protocol.
ticast data throughout the network. The SPT created by PIM DM is based on
source tree distribution.
unicast route table to verify that the interface leads toward the source. It then
forwards the data to all PIM neighbors. Those PIM neighbors then forward
the data to their PIM neighbors. This happens throughout the network