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Chapter 14: IGMP Snooping Querier
174
with the second lowest IP address is made the standby querier, again by
switch 2. In the case where there are three queriers, the switch in the
network with IGMP snooping enabled and IGMP querier disabled
determines the standby querier and then the second standby querier by
comparing their IP addresses.
The following example consists of a LAN with three switches. See
Figure 62. IGMP snooping is enabled on all three switches. However,
IGMP snooping querier is enabled on switches 1 and 3. Switch 2
determines that switch 1 has the lowest IP routing address and forwards
all multicast packets to switch 1, making switch 1 the active querier.
Switch 3 becomes the standby querier in case switch 1 stops transmitting
query packets.
Note
Switches 1 and 3 are only sending queriers. Neither switch detects
nor displays an opposing querier.
Figure 62. IGMP Snooping Querier with Two Queriers
Multicast source:
IP address: 149.123.48.1
Switch 1:
VLAN: Default_VLAN
Routing interface:
149.123.48.2
Host nodes:
IP addresses:
149.123.48.3 to 149.123.48.24
Host nodes with IP addresses:
149.123.48.41 to 149.123.48.62
Switch 3:
VLAN: Default_VLAN
Routing interface:
149.123.48.4
Switch 2:
VLAN: Default_VLAN
Routing interface:
149.123.48.3
Host nodes:
IP addresses:
149.123.48.25 to 149.123.48.40