Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Software Configuration Guide, Release 12.2(33)MRB
OL-21227-02
Chapter 1 Cisco MWR 2941 Router Overview
Features
Multicast Routing
The following sections describe the support for multicast routing on the Cisco MWR 2941.
• Role of IP Multicast in Information Delivery
• Multicast Group Transmission Scheme
• IP Multicast Group Addressing
• IP Multicast Address Scoping
• Layer 2 Multicast Addresses
• IP Multicast Delivery Modes
• Protocol Independent Multicast
• Multicast Group Modes
• Rendezvous Points
• Multicast Forwarding
Role of IP Multicast in Information Delivery
IP multicast is a bandwidth-conserving technology that reduces traffic by delivering a single stream of
information simultaneously to potentially thousands of businesses and homes. Applications that take
advantage of multicast include video conferencing, corporate communications, distance learning, and
distribution of software, stock quotes, and news.
IP multicast routing enables a host (source) to send packets to a group of hosts (receivers) anywhere
within the IP network by using a special form of IP address called the IP multicast group address. The
sending host inserts the multicast group address into the IP destination address field of the packet and
IP multicast routers and multilayer switches forward incoming IP multicast packets out all interfaces that
lead to the members of the multicast group. Any host, regardless of whether it is a member of a group,
can send to a group. However, only the members of a group receive the message.
Multicast Group Transmission Scheme
IP communication consists of hosts that act as senders and receivers of traffic as shown in Figure 5.
Senders are called sources. Traditional IP communication is accomplished by a single host source
sending packets to another single host (unicast transmission) or to all hosts (broadcast transmission). IP
multicast provides a third scheme, allowing a host to send packets to a subset of all hosts (multicast
transmission). This subset of receiving hosts is called a multicast group. The hosts that belong to a
multicast group are called group members.
Multicast is based on this group concept. A multicast group is an arbitrary number of receivers that join
a group in order to receive a particular data stream. This multicast group has no physical or geographical
boundaries—the hosts can be located anywhere on the Internet or on any private internetwork. Hosts that
are interested in receiving data from a source to a particular group must join that group. Joining a group
is accomplished by a host receiver by way of the Internet Group Management Protocol (IGMP).
In a multicast environment, any host, regardless of whether it is a member of a group, can send to a
group. However, only the members of a group can receive packets sent to that group. Multicast packets
are delivered to a group using best-effort reliability, just like IP unicast packets.