Table of Contents
Advertisement
multicast group address in the destination address field of the IP packet. The multicast model differs
from the unicast model in that a multicast packet must be forwarded to several external interfaces to
send the packet to all receiving stations, i.e., multicast forwarding is more complex than unicast
forwarding.
To ensure the multicast packets reach the routers using the shortest route, the multicast protocols
must check the receiving interfaces of the multicast packets against the unicast route table or route
table dedicated for multicast (such as a DVMRP route table). This checking mechanism is the base
for most multicast routing protocols to perform forwarding, and is called Reverse Path Forwarding
(RPF). Multicast routers use the source address of an arrived multicast packet to query the unicast
route table or an independent multicast route table to make sure the ingress interface from which the
packet arrived is in the shortest route from the receiving station to the source address. If an active
tree is used, the source address is the address of source host sending the multicast packet; if a shared
tree is used, the source address is the root address of that shared tree. When a multicast packet
arrives at a router, the packet will be forwarded according to the multicast forwarding rules if the
RPF check is ok; otherwise, the packet will be discarded.
19.1.4 Application of Multicast
IP multicast technology effectively solved the problem of one sender vs. multiple receivers,
fulfilling the high efficiency data transmission from one point to multiple points in the IP network,
and can significantly save the network bandwidth and reduce network traffic. The multicast feature
can be conveniently used to provide some new value-added services, including online live broadcast,
network TV, remote education, remote medical service, network radio, real-time video/audio
meeting that can be summarized in the following three fields:
1)
Multimedia and stream applications.
2)
Data warehouse and financial (like stocks) applications.
3)
Any point-to-multiple-points data distribution applications.
With the increasing of multimedia services in the IP network, multicast represents great market
potential, and multicast service is widely used and spreading quickly.
19.2 Common Multicast Configurations
19.2.1 Common Multicast Configuration Commands
show ip mroute
19.2.1.1 show ip mroute
Command: show ip mroute [group_address] [source_address]
EES4710BD 10 Slots L2/L3/L4 Chassis Switch
459
Advertisement
Table of Contents
Troubleshooting
