Multicast Address Properties - Cisco 500 Series Administration Manual

Multicast
Multicast Forwarding
NOTE
Cisco 500 Series Managed Switch Administration Guide
If the IGMP/MLD querier election mechanism is disabled, then the IGMP/MLD
Snooping Querier delays sending general query messages after its enabling for
60 seconds. If there is no other querier, it starts to send general query messages. It
stops sending general query messages if it detects another querier.
The IGMP/MLD Snooping querier resumes sending general query messages if it
does hear another querier for the following interval:
Query passive interval = Robustness * Query Interval + 0.5*Query Response
Interval.
It is recommended to disable IGMP/MLD Querier election mechanism if there is an
IPM Multicast router on the VLAN.

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 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.
IGMP/MLD Proxy
IGMP/MLD Proxy is a simple IP Multicast protocol.
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