Multicast
Defining Multicast Properties
239 Cisco Small Business 300 Series Managed Switch Administration Guide
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If the device is enabled as an IGMP Querier, it starts after 60 seconds have passed
with no IGMP traffic (queries) detected from a Multicast router. In the presence of
other IGMP Queriers, the device might (or might not) stop sending queries, based
on the results of the standard querier selection process.

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:
-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 Layer2 addres s.
-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.
Defining Multicast Properties
The Properties page enables you to configure the Bridge Multicast filtering status.
By default, all Multicast frames are flooded to all ports of the VLAN. To selectively
forward only to relevant ports and filter (drop) the Multicast on the rest of the ports,
enable Bridge Multicast filtering status in the Properties page.
If filtering is enabled, Multicast frames are forwarded to a subset of the ports in the
relevant VLAN as defined in the Multicast Forwarding Data Base. Multicast filtering
is enforced on all traffic. By default, such traffic is flooded to all relevant ports, but
you can limit forwarding to a smaller subset.