Qtech QSW-2900-24T-AC [87/209] Multicast protocol configuration

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Chapter 5 Multicast Protocol Configuration

5.1 Multicast overview

5.1.1 Multicast Address

As receivers are multiple hosts in a multicast group, you should be concerned about the following questions:

· What destination should the information source send the information to in the multicast mode?

· How to select the destination address, that is, how does the information source know who the user is?

These questions are about multicast addressing. To enable the communication between the information source

and members of a multicast group (a group of information receivers), network-layer multicast addresses, namely, IP

multicast addresses must be provided. In addition, a technology must be available to map IP multicast addresses to

link-layer MAC multicast addresses. The following sections describe these two types of multicast addresses:

a) IP multicast address

Internet Assigned Numbers Authority (IANA) categorizes IP addresses into five classes: A, B, C, D, and E.

Unicast packets use IP addresses of Class A, B, and C based on network scales. Class D IP addresses are used as

destination addresses of multicast packets. Class D address must not appear in the IP address field of a source IP

address of IP packets. Class E IP addresses are reserved for future use.

In unicast data transport, a data packet is transported hop by hop from the source address to the destination

address. In an IP multicast environment, there are a group of destination addresses (called group address), rather than

one address. All the receivers join a group. Once they join the group, the data sent to this group of addresses starts to

be transported to the receivers. All the members in this group can receive the data packets. This group is a multicast

group.

A multicast group has the following characteristics:

· The membership of a group is dynamic. A host can join and leave a multicast group at any time.

· A multicast group can be either permanent or temporary.

· A multicast group whose addresses are assigned by IANA is a permanent multicast group. It is also

called reserved multicast group.

Note that:

· The IP addresses of a permanent multicast group keep unchanged, while the members of the group

can be changed.

· There can be any number of, or even zero, members in a permanent multicast group.

· Those IP multicast addresses not assigned to permanent multicast groups can be used by temporary

multicast groups.

Class D IP addresses range from 224.0.0.0 to 239.255.255.255. For details, see Table 1-1.

Table 1-1 Range and description of Class D IP addresses

Class D address range Description