Supported Platforms
Example: Configuring IGMP Snooping
 | Note: This example uses Junos OS for EX Series switches with support for the Enhanced Layer 2 Software (ELS) configuration style. If your switch runs software that does not support ELS, see, Example: Configuring IGMP Snooping on EX Series Switches. For ELS details, see, Getting Started with Enhanced Layer 2 Software. |
You can enable IGMP snooping on a VLAN to constrain the flooding of IPv4 multicast traffic on a VLAN. When IGMP snooping is enabled, a switch examines IGMP messages between hosts and multicast routers and learns which hosts are interested in receiving multicast traffic for a multicast group. Based on what it learns, the switch then forwards multicast traffic only to those interfaces that are connected to relevant receivers instead of flooding the traffic to all interfaces.
This example describes how to configure IGMP snooping:
Requirements
This example uses the following hardware and software components:
- One EX4300 Series switch
- Junos OS Release 13.2X50-D10 or later for EX Series switches
Before you configure IGMP snooping, be sure you have:
- Configured a VLAN, vlan100, on the switch
- Assigned interfaces ge-0/0/0, ge-0/0/1, ge-0/0/2, and ge-0/0/12 to vlan100
- Configured ge-0/0/12 as a trunk interface
See Configuring VLANs for EX Series Switches (CLI Procedure).
Overview and Topology
In this example, interfaces ge-0/0/0, ge-0/0/1, and ge-0/0/2 on the switch are in vlan100 and are connected to hosts that are potential multicast receivers. Interface ge-0/0/12, a trunk interface also in vlan100, is connected to a multicast router. The router acts as the IGMP querier and forwards multicast traffic for group 225.100.100.100 to the switch from a multicast source.
The sample topology is illustrated in Figure 1.
Figure 1: IGMP Snooping Topology Sample Topology
In this sample topology, the multicast router forwards multicast traffic to the switch from the source when it receives a membership report for group 255.100.100.100 from one of the hosts—for example, Host B. If IGMP snooping is not enabled on vlan100, the switch floods the multicast traffic on all interfaces in vlan100 (except for interface ge-0/0/12). If IGMP snooping is enabled on vlan100, the switch monitors the IGMP messages between the hosts and router, allowing it to determine that only Host B is interested in receiving the multicast traffic. The switch then forwards the multicast traffic only to interface ge-0/0/1.
This example shows how to perform the following optional configurations, which can reduce group join and leave latency:
- Configure immediate leave on the VLAN. When immediate
leave is configured, the switch stops forwarding multicast traffic
on an interface when it detects that the last member of the multicast
group has left the group. If immediate leave is not configured, the
switch waits until the group-specific queries time out before it stops
forwarding traffic.
Immediate leave is supported by IGMP version 2 (IGMPv2) and IGMPv3. With IGMPv2, we recommend that you configure immediate leave only when there is only one IGMP host on an interface. In IGMPv2, only one host on a interface sends a membership report in response to a group-specific query—any other interested hosts suppress their reports to avoid a flood of reports for the same group. This report-suppression feature implies that the switch knows about only one interested host at any given time.
- Configure ge-0/0/12 as a static multicast-router interface. In this topology, ge-0/0/12 always leads to the multicast router. By statically configuring ge-0/0/12 as a multicast-router interface, you avoid any delay imposed by the switch having to learn that ge-0/0/12 is a multicast-router interface.
Configuration
To configure IGMP snooping on a switch:
CLI Quick Configuration
To quickly configure IGMP snooping, copy the following commands and paste them into the switch terminal window:
[edit]
set protocols
igmp-snooping vlan vlan100 immediate-leave
set protocols igmp-snooping vlan vlan100
interface ge-0/0/12 multicast-router-interface
Step-by-Step Procedure
To configure IGMP snooping on vlan100:
- Configure the switch to immediately remove a group membership
from an interface when it receives a leave report from the last member
of the group on the interface:
[edit protocols]
user@switch# set igmp-snooping vlan vlan100 immediate-leave - Statically configure interface ge-0/0/12 as a multicast-router
interface:
[edit protocols]
user@switch# set igmp-snooping vlan vlan100 interface ge-0/0/12 multicast-router-interface
Results
Check the results of the configuration:
[edit protocols]
user@switch# show igmp-snooping
vlan vlan100 {
immediate-leave;
interface ge-0/0/12.0 {
multicast-router-interface;
}
}Verifying IGMP Snooping Operation
To verify that IGMP snooping is operating as configured, perform the following task:
Displaying IGMP Snooping Information for VLAN vlan100
Purpose
Verify that IGMP snooping is enabled on vlan100 and that ge-0/0/12 is recognized as a multicast-router interface.
Action
Enter the following command:
user@switch>show igmp snooping membership
VLAN: vlan100
Interfaces: ge-0/0/12.0,
Meaning
By showing information for vlan100, the command output confirms that IGMP snooping is configured on the VLAN. Interface ge-0/0/12.0 is listed as a multicast-router interface, as configured. Because none of the host interfaces are listed, none of the hosts are currently receivers for the multicast group.
