Configuring Multicast Forwarding
Multicast Forwarding
Cisco Small Business 200 1.1 Series Smart Switch Administration Guide
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IGMP/MLD snooping can effectively reduce Multicast traffic from streaming
bandwidth-intensive IP applications. A switch using IGMP/MLD snooping only
forwards Multicast traffic to the hosts interested in that traffic. This reduction of
Multicast traffic reduces the packet processing at the switch, and also reduces the
workload of the end hosts, since they do not have to receive and filter all of the
Multicast traffic generated in the network.
The following versions are supported:
•
IGMP v1/v2/ v3
•
MLD v1/v2
Multicast Address Properties
Multicast addresses have the following properties:
•
Each IPv4 Multicast address is in the address range 224.0.0.0 to
239.255.255.255.
•
The IPv6 Multicast address is FF00:/8.
•
To map an IP Multicast group address to an Layer 2 Multicast address:
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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,
234.129.2.3 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.
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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.