Cisco Catalyst 3750-X User Manual

23-4
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 23 Configuring Flex Links and the MAC Address-Table Move Update Feature
Understanding Flex Links and the MAC Address-Table Move Update
Leaking IGMP Reports
To achieve multicast traffic convergence with minimal loss, a redundant data path must be set up before
the Flex Link active link goes down. This can be achieved by leaking only IGMP report packets on the
Flex Link backup link. These leaked IGMP report messages are processed by upstream distribution
routers, so multicast data traffic gets forwarded to the backup interface. Because all incoming traffic on
the backup interface is dropped at the ingress of the access switch, no duplicate multicast traffic is
received by the host. When the Flex Link active link fails, the access switch starts accepting traffic from
the backup link immediately. The only disadvantage of this scheme is that it consumes bandwidth on the
link between the distribution switches and on the backup link between the distribution and access
switches. This feature is disabled by default and can be configured by using the switchport backup
interface interface-id multicast fast-convergence command.
When this feature has been enabled at changeover, the swi
tch does not generate the proxy reports on the
backup port, which became the forwarding port.
Configuration Examples
These are configuration examples for learning the other Flex Link port as the mrouter port when Flex
Link is configured on GigabitEthernet1/0/11 and GigabitEthernet1/0/12, and output for the
show interfaces switchport backup co
mmand:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface Gigabit
Ethernet1/0/11
Switch(config-if)# switchport tru
nk encapsulation dot1q
Switch(config-if)# switchport mod
e trunk
Switch(config-if)# switchport bac
kup interface Gi1/0/12
Switch(config-if)# exit
Switch(config)# interface Gigabit
Ethernet1/0/12
Switch(config-if)# switchport tru
nk encapsulation dot1q
Switch(config-if)# switchport mod
e trunk
Switch(config-if)# end
Switch# s
how interfaces switchport backup detail
Switch Backup Interface Pairs:
Active Interface Backup Interface State
GigabitEthernet1/0/11 GigabitEthernet1/0/12 Active Up/Backup Standby
Preemption Mode : off
Multicast Fast Convergence : Off
Bandwidth : 100000 Kbit (Gi1/0/11), 100000 Kbit (Gi1/0/12)
Mac Address Move Update Vlan : auto
This output shows a querier for VLANs 1 and 401, with their queries reaching the switch through
GigabitEthernet1/0/11:
Switch# show ip igmp snooping querier
Vlan IP Address IGMP Version Port
-------------------------------------------------------------
1 1.1.1.1 v2 Gi1/0/11
401 41.41.41.1 v2 Gi1/0/11
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)

Cisco Catalyst 3750-X Specifications

General

Switching Capacity	160 Gbps
Stacking Bandwidth	64 Gbps
Max Stacking Units	9
Layer Support	Layer 2 and Layer 3
Form Factor	Rack-mountable
DRAM	256 MB
Flash Memory	64 MB
Model	Cisco Catalyst 3750-X Series
Ports	24 or 48 10/100/1000 Ethernet ports
Uplink Interfaces	4 SFP or 2 SFP+
Features	StackWise Plus, EnergyWise
Image	IP Base or IP Services
Operating Temperature	0 to 40°C
Operating Humidity	10 to 85% noncondensing