Which statement is true of a source that wants to transmit multicast traffic to group 239.1.1.1?
A.
Before sending traffic, it must first join multicast group 239.1.1.1 by sending an IGMPv2
membership report to the default router on the local subnet.
B.
It must send an IGMPv2 Request to Send packet and then wait for an IGMPv2 Clear to Send
packet from the IGMPv2 querier router on the local subnet
C.
It may begin transmitting multicast traffic to the group only when there is no other host
transmitting to the group on the local subnet.
D.
It may transmit multicast traffic to the group at any time.
Explanation:
IP multicast is a method of sending Internet Protocol (IP) datagrams to a group of interested
receivers in a single transmission. It is often employed for streaming media applications on the
Internet and private networks.
The method is the IP-specific version of the general concept of multicast networking. It uses
specially reserved multicast address blocks in IPv4 and IPv6. In IPv6, IP multicast addressingreplaces broadcast addressing as implemented in IPv4.
Key concepts in IP multicast include an IP multicast group address, [3] a multicast distribution tree
and receiver driven tree creation.[4]
An IP multicast group address is used by sources and the receivers to send and receive multicast
messages. Sources use the group address as the IP destination address in their data packets.
Receivers use this group address to inform the network that they are interested in receiving
packets sent to that group. For example, if some content is associated with group 239.1.1.1, the
source will send data packets destined to 239.1.1.1. Receivers for that content will inform the
network that they are interested in receiving data packets sent to the group 239.1.1.1. The
receiver joins 239.1.1.1. The protocol typically used by receivers to join a group is called the
Internet Group Management Protocol (IGMP).
With routing protocols based on shared trees, once the receivers join a particular IP multicast
group, a multicast distribution tree is constructed for that group. The protocol most widely used for
this is Protocol Independent Multicast (PIM). It sets up multicast distribution trees such that data
packets from senders to a multicast group reach all receivers which have joined the group. For
example, all data packets sent to the group 239.1.1.1 are received by receivers who joined
239.1.1.1. There are variations of PIM implementations: Sparse Mode (SM), Dense Mode (DM),
Source Specific Mode (SSM) and Bidirectional Mode (Bidir, or Sparse-Dense Mode, SDM). Of
these, PIM-SM is the most widely deployed as of 2006; SSM and Bidir are simpler and scalable
variations developed more recently and are gaining in popularity.http://en.wikipedia.org/wiki/IP_multicast