3com 3031 Instruccion De Instalación
614
C
HAPTER
48: PIM C
ONFIGURATION
correct. Otherwise, the multicast packet will be discarded as a redundant one. The
concerned unicast routing information can be of any unicast routing protocol such
as RIP or OSPF.
concerned unicast routing information can be of any unicast routing protocol such
as RIP or OSPF.
Assert mechanism
As shown in Figure 147, Routers A and B are on the same LAN network segment
but have different paths to the multicast source S. Therefore, both will forward the
multicast packet received from S over the LAN and the multicast router C at the
downstream node will receive two identical multicast packets.
but have different paths to the multicast source S. Therefore, both will forward the
multicast packet received from S over the LAN and the multicast router C at the
downstream node will receive two identical multicast packets.
Figure 147 Assert mechanism diagram
In this case, the assert mechanism helps in choosing a single forwarder. By sending
an Assert packet, a router can find the shortest path. If two or more paths have
the same priority and cost, the IP address of the forwarding routers along the
paths is used in making the decision. The one with a greater IP address is selected
as the upstream neighbor of the (S, G) entry, and is responsible for forwarding the
(S, G) multicast packet.
an Assert packet, a router can find the shortest path. If two or more paths have
the same priority and cost, the IP address of the forwarding routers along the
paths is used in making the decision. The one with a greater IP address is selected
as the upstream neighbor of the (S, G) entry, and is responsible for forwarding the
(S, G) multicast packet.
Grafting
When a pruned downstream node needs to be restored to the forwarding state, it
may send a graft packet to the upstream node.
may send a graft packet to the upstream node.
PIM-SM
PIM-SM (Protocol Independent Multicast, Sparse Mode) is a kind of multicast
routing protocol, mainly used in large-scaled networks where group members are
scattered sparsely.
routing protocol, mainly used in large-scaled networks where group members are
scattered sparsely.
In contrast to PIM-DM, PIM-SM assumes that no host needs the multicast packets,
unless there is an explicit request.
unless there is an explicit request.
PIM-SM sends multicast information to all PIM-SM routers by configuring the RP
(Rendezvous Point) and the BSR (Bootstrap Router) and builds the RP-rooted
shared tree (RPT) using the join/prune information of the routers., To reduce the
bandwidth occupied by data packets and control packetsas well as the processing
costs. Multicast data flows along the shared tree to the network segments where
the multicast group members are. When the data traffic is massive, the SPT
(Shortest Path Tree) rooted on the source can be used to reduce network delay.
(Rendezvous Point) and the BSR (Bootstrap Router) and builds the RP-rooted
shared tree (RPT) using the join/prune information of the routers., To reduce the
bandwidth occupied by data packets and control packetsas well as the processing
costs. Multicast data flows along the shared tree to the network segments where
the multicast group members are. When the data traffic is massive, the SPT
(Shortest Path Tree) rooted on the source can be used to reduce network delay.
Receiver
Router A
Router B
Router C
Multicast datagram forw arded by the upstream node
Receiver
Router A
Router B
Router C
Multicast datagram forw arded by the upstream node