Multicast forwarding enables one-to-many information dissemination. Multicast applicationsare useful for dissemination of information to multiple clients, where clients do not require reception of the entire content. A typical application is a cable-TV-like service, where clients can join a channel in the middle of a transmission, and leave before it ends.
The data is sent only to relevant ports. Forwarding the data only to the relevant ports conservesbandwidth and host resources on links. By default, all Multicast frames are flooded to all ports of the VLAN. It is possible to selectively forward only to relevant ports and filter (drop) the Multicast on the rest of the ports by enabling the Bridge Multicast filtering status in this section.
Multicast addresses have the following properties:
Each IPv4 Multicast address is in the address range 184.108.40.206 to 220.127.116.11.
The IPv6 Multicast address is FF00:/8.
To map an IP Multicast group address to an Layer 2 Multicast address:
For IPv4, this is mapped by taking the 23 low-order bits from the IPv4 address, and adding them to the 01:00:5e prefix. By standard, the upper nine bits of the IP address are ignored, and any IP addresses that only differ in the value of these upper bits are mapped to the same Layer 2 address, since the lower 23 bits that are used are identical. For example, 18.104.22.168 is mapped to a MAC Multicast group address 01:00:5e:01:02:03. Up to 32 IP Multicast group addresses can be mapped to the same Layer 2 address.
For IPv6, this is mapped by taking the 32 low-order bits of the Multicast address, and adding the prefix of 33:33. For example, the IPv6 Multicast address FF00::1122:3344 is mapped to Layer 2 Multicast 33:33:11:22:33:44.
To enable Multicast filtering, and select the forwarding method, follow these steps:
Click Multicast > Properties.
Enter the parameters.
Click Apply. The Running Configuration file is updated.