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19-5
Catalyst 2960 and 2960-S Switch Software Configuration Guide
OL-8603-09
Chapter 19 Configuring Flex Links and the MAC Address-Table Move Update Feature
Understanding Flex Links and the MAC Address-Table Move Update
Preemption Mode : off
Multicast Fast Convergence : Off
Bandwidth : 100000 Kbit (Gi0/11), 100000 Kbit (Gi0/12)
Mac Address Move Update Vlan : auto
This output shows a querier for VLANs 1 and 401, with their queries reaching the switch through Gigabit
Ethernet0/11:
Switch# show ip igmp snooping querier
Vlan IP Address IGMP Version Port
-------------------------------------------------------------
1 1.1.1.1 v2 Gi0/11
401 41.41.41.1 v2 Gi0/11
Here is output for the show ip igmp snooping mrouter command for VLANs 1 and 401:
Switch# show ip igmp snooping mrouter
Vlan ports
---- -----
1 Gi1/0/11(dynamic), Gi1/0/12(dynamic)
401 Gi1/0/11(dynamic), Gi1/0/12(dynamic)
Similarly, both Flex Link ports are part of learned groups. In this example, Gigabit Ethernet0/11 is a
receiver/host in VLAN 1, which is interested in two multicast groups:
Switch# show ip igmp snooping groups
Vlan Group Type Version Port List
-----------------------------------------------------------------------
1 228.1.5.1 igmp v2 Gi1/0/11, Gi1/0/12, Gi2/0/11
1 228.1.5.2 igmp v2 Gi1/0/11, Gi1/0/12, Gi2/0/11
When a host responds to the general query, the switch forwards this report on all the mrouter ports. In
this example, when a host sends a report for the group 228.1.5.1, it is forwarded only on Gigabit
Ethernet0/11, because the backup port Gigabit Ethernet0/12 is blocked. When the active link, Gigabit
Ethernet0/11, goes down, the backup port, Gigabit Ethernet0/12, begins forwarding.
As soon as this port starts forwarding, the switch sends proxy reports for the groups 228.1.5.1 and
228.1.5.2 on behalf of the host. The upstream router learns the groups and starts forwarding multicast
data. This is the default behavior of Flex Link. This behavior changes when the user configures fast
convergence using the switchport backup interface gigabitEthernet 0/12 multicast fast-convergence
command. This example shows turning on this feature:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet 0/11
Switch(config-if)# switchport backup interface gigabitethernet 0/12 multicast
fast-convergence
Switch(config-if)# exit
Switch# show interfaces switchport backup detail
Switch Backup Interface Pairs:
Active Interface Backup Interface State
------------------------------------------------------------------------
GigabitEthernet0/11 GigabitEthernet0/12 Active Up/Backup Standby
Preemption Mode : off
Multicast Fast Convergence : On
Bandwidth : 100000 Kbit (Gi0/11), 100000 Kbit (Gi0/12)
Mac Address Move Update Vlan : auto
This output shows a querier for VLAN 1 and 401 with their queries reaching the switch through Gigabit
Ethernet0/11:
Switch# show ip igmp snooping querier
Vlan IP Address IGMP Version Port