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Page 19 | AlliedWare™ OS How To Note: IGMP
Multiple potential IGMP queriers > Explanation of Multiple potential IGMP queriers
To see the difference between a switch acting as a Snooper and a switch acting as a Querier,
compare the IGMP snooping table for switch 1 (above) with its IGMP table (below). They
seem to contradict each other. The IGMP snooping table tells us that switch 1 is aware that it
is receiving the group 224.12.
1
3.
1
4 and will send all groups (including this one) out port 49
towards the IGMP Querier, switch 2. However, the IGMP table shows that IGMP has not
registered any interested clients—the group list is empty.
This disparity between the IGMP snooping table and the IGMP table simply shows that
switch 1 is acting as a Snooper because it did not become the Querier. The IGMP table on
switch 1 has no entries because no Report message has been seen on switch 1. The disparity
does not appear in the output for switch 2, because switch 2 is the Querier. The IGMP and
IGMP snooping tables show the same group entries on switch 2.
Manager Switch 1> show ip igmp
IGMP Protocol
------------------------------------------------------------------------
Status ........................... Enabled
Default Query Interval ........... 125 secs
Default Timeout Interval ......... 260 secs
Last Member Query Interval ....... 10 (1/10secs)
Last Member Query Count .......... 2
Robustness Variable .............. 2
Query Response Interval .......... 100 (1/10secs)
Disabled All-groups ports ........ None
Interface Name .......... vlan100
Other Querier timeout ... 214 secs
Group List ..............
------------------------------------------------------------------------
Manager Switch 2> show ip igmp
IGMP Protocol
------------------------------------------------------------------------
Status ........................... Enabled
Default Query Interval ........... 125 secs
Default Timeout Interval ......... 260 secs
Last Member Query Interval ....... 10 (1/10secs)
Last Member Query Count .......... 2
Robustness Variable .............. 2
Query Response Interval .......... 100 (1/10secs)
Disabled All-groups ports ........ None
Interface Name .......... vlan100 (DR)
IGMP Proxy .............. Off
Group List ..............
Group. 224.12.13.14 Last Adv. 172.31.0.222 Refresh time 228 secs
Ports 2
------------------------------------------------------------------------