IGMP Snooping Configuration
This chapter describes how to configure Internet Group Management Protocol (IGMP) Snooping.
Note: Run the switchport command on each port to change to Layer-2 mode.
Without IGMP, Layer-2 switches handle IP multicast traffic in the same manner as broadcast traffic and forwards frames received on one interface to all other interfaces. This creates excessive traffic on the network, and affects network performance. IGMP Snooping allows switches to monitor network traffic, and determine hosts to receive multicast traffic. Only one membership report is relayed from a group, instead of a report from each host in the group. To achieve this, IGMP Snooping is enabled on the switches.
Topology
This example describes the configuration on switch S1. The eth1 interface is configured as a multicast router port.
Because IGMP Snooping is used in bridged LAN environments, router R1 does not require running IGMP Snooping, and can run any multicast protocol (such as PIM-SM). Thus, the configuration on R1 is not included in this example.
IGMP Snooping Topology
As a result of this configuration:
• The switch itself replies with membership report messages in response to queries received on interface eth1. However, if you do not enable report suppression on the switch, when it receives an IGMP Query message on eth1, it forwards it to both Host A and Host B. As a result, both hosts reply with a Membership report (as Layer-2 IGMP is running on the hosts).
• Because Host A and Host B are members of the same multicast group, the router is not notified when A leaves the group, because the group still has another member. When Host B leaves the group, the switch will send a Leave message to the Router with the destination address as 224.0.0.2 (All Router Destination Address).
Configuration
To enable IGMP Snooping on an interface:
1. Add a bridge to the spanning-tree table
2. Specify the interface to be configured
3. Associate the interface with bridge group
4. IGMP snooping will be enabled by default
5. Configure ports that are connected to routers as multicast router ports
6. By default, IGMP report suppression is enabled on the switch
S1
#configure terminal | Enter the Configure mode. |
(config)#bridge 1 protocol ieee vlan-bridge | Add bridge 1 to the spanning-tree table. |
(config)#vlan database | enter VLAN mode |
(config-vlan)# vlan 2 bridge 1 | Create VLAN and add it to bridge 1 |
(config)#exit | Exit VLAN mode |
(config)#interface eth3 | Specify the interface eth3 to be configured, and Enter interface mode. |
(config-if)#shutdown | Shut down the interface. |
(config-if)#switchport | Configure the interface as a switch port. |
(config-if)#bridge-group 1 | Associate the interface eth1 with bridge-group 1. |
(config-if)#switchport mode trunk | Configure the port as an trunk port. |
(config-if)#switchport trunk allowed vlan all | Add VLAN to trunk |
(config-if)#no shutdown | Bring up the interface. |
(config-if)#exit | Exit interface mode. |
(config)#interface eth1 | Specify interface eth1 to be configured. |
(config-if)#shutdown | Shut down the interface. |
(config-if)#switchport | Configure the interface as a switch port. |
(config-if)#bridge-group 1 | Associate interface eth1 with bridge-group 1. |
(config-if)#switchport mode trunk | Configure the port as an trunk port. |
(config-if)#switchport trunk allowed vlan all | Add VLAN to trunk |
(config-if)#no shutdown | Bring up the interface. |
(config-if)#exit | Exit interface mode. |
(config)#interface eth2 | Specify interface eth2 to be configured. |
(config-if)#shutdown | Shut down the interface. |
(config-if)#switchport | Configure the interface as a switch port. |
(config-if)#bridge-group 1 | Associate interface eth2 with bridge-group 1. |
(config-if)#switchport mode trunk | Configure the port as an trunk port. |
(config-if)#switchport trunk allowed vlan all | Add VLAN to trunk |
(config-if)#no shutdown | Bring up the interface. |
(config-if)#exit | Exit interface mode. |
(config)#interface vlan1.2 | Specify interface vlan1.1 to be configured. |
(config)#ip address 1.2.3.4/24 | Specify IP address |
(config-if)# igmp snooping mrouter interface eth1 | Configure this port as a multicast router port |
(config-if)#exit | Exit interface mode |
Validation
#show running-config interface eth3
!
interface eth3
switchport
bridge-group 1
switchport mode trunk
switchport trunk allowed vlan add 2
#show running-config interface eth1
!
interface eth1
switchport
bridge-group 1
switchport mode trunk
switchport trunk allowed vlan add 2
#show running-config interface eth2
!
interface eth2
switchport
bridge-group 1
switchport mode trunk
switchport trunk allowed vlan add 2
#show igmp snooping groups
IGMP Snooping Group Membership
Group source list: (R - Remote, S - Static)
Vlan Group/Source Address Interface Flags Uptime Expires Last Reporter Version
2 224.1.1.1 eth3 R 00:00:03 00:04:17 0.0.0.0 V3
2 224.1.1.1 eth2 R 00:00:03 00:04:17 0.0.0.0 V3
#show igmp snooping interface vlan1.2
IGMP Snooping information for vlan1.2
IGMP Snooping enabled
Snooping Querier none
IGMP Snooping other querier timeout is 255 seconds
Group Membership interval is 260 seconds
IGMPv2 fast-leave is disabled
IGMPv1/v2 Report suppression enabled
IGMPv3 Report suppression enabled
Router port detection using IGMP Queries
Number of router-ports: 1
Number of Groups: 1
Number of v1-reports: 0
Number of v2-reports: 0
Number of v2-leaves: 0
Number of v3-reports: 2
Active Ports:
Eth3
Eth1
Eth2