Multimedia Traffic Control with IP Multicast (IGMP)

More on IGMP Operation

HPswitch(vlan-1)# no ip igmp querier

N o t e

A Querier is required for proper IGMP operation. For this reason, if you disable the Querier function on the switch, ensure that there is an IGMP Querier (and, preferably, a backup Querier) available on the same VLAN.

If the switch becomes the Querier for a particular VLAN (for example, the DEFAULT_VLAN), then subsequently detects queries transmitted from another device on the same VLAN, the switch ceases to operate as the Querier for that VLAN. If this occurs, the switch Event Log lists a pair of messages similar to these:

I01/15/01 09:01:13 igmp: DEFAULT_VLAN: Other Querier detected

I01/15/01 09:01:13 igmp: DEFAULT_VLAN: This switch is no longer Querier

In the above scenario, if the other device ceases to operate as a Querier on the default VLAN, then the switch detects this change and can become the Querier as long as it is not preempted by some other IGMP Querier on the VLAN. In this case, the switch Event Log lists messages similar to the following to indicate that the switch has become the Querier on the VLAN:

I01/15/01 09:21:55 igmp: DEFAULT_VLAN: Querier Election in process

I01/15/01 09:22:00 igmp: DEFAULT_VLAN: This switch has been elected as Querier

Excluding Well-Known or Reserved Multicast Addresses from IP Multicast Filtering

Each multicast host group is identified by a single IP address in the range of

224.0.0.0through 239.255.255.255 (which corresponds to the Ethernet multi- cast address range of 01005e-000000 through 01005e-7fffff). Specific groups of consecutive addresses in this range are termed “well-known” addresses and are reserved for predefined host groups. IGMP does not filter these addresses, so any packets the switch receives for such addresses are flooded out all ports assigned to the VLAN on which they were received (except the port on which the packets entered the VLAN). The following table lists the 32 well-known address groups (8192 total addresses) that IGMP does not filter on the Series 5300XL switches.

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