4-22
Multimedia Traffic Control with IP Multicast (IGMP)
Excluding Multicast Addresses from IP Multicast Filtering
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 pre-empted 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:
I 01/15/01 09:21:55 igmp: DEFAULT_VLAN: Querier Election in
process
I 01/15/01 09:22:00 igmp: DEFAULT_VLAN: This switch has been
elected as Querier
Excluding Multicast Addresses from IP
Multicast Filtering
Each multicast host group is identified by a single IP address in the range of
224.0.0.0 through 239.255.255.255. 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 switches covered in this guide, as
well as on the 1600M, 2400M, 2424M, 2650M, 4000M, 6108M, 8000M, and Switch
2500 Series devices.
Table 4-3.IP Multicast Address Groups Excluded from IGMP Filtering
Groups of Consecutive Addresses in
the Range of 224.0.0.X to 239.0.0.X*
Groups of Consecutive Addresses in
the Range of 224.128.0.X to 239.128.0.X*
224.0.0.x 232.0.0.x 224.128.0.x 232.128.0.x
225.0.0.x 233.0.0.x 225.128.0.x 233.128.0.x
226.0.0.x 234.0.0.x 226.128.0.x 234.128.0.x
227.0.0.x 235.0.0.x 227.128.0.x 235.128.0.x
228.0.0.x 236.0.0.x 228.128.0.x 236.128.0.x
229.0.0.x 237.0.0.x 229.128.0.x 237.128.0.x
230.0.0.x 238.0.0.x 230.128.0.x 238.128.0.x
231.0.0.x 239.0.0.x 231.128.0.x 239.128.0.x
* X is any value from 0 to 255.
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