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IGMP snooping

Internet Group Management Protocol (IGMP) snooping allows Sophos Switch to identify multicast groups and intelligently forward multicast traffic.

Multicast groups are endpoint devices using multicast applications such as video conferencing or audio streaming and wanting to receive multicast packets.

IGMP version Description
IGMPv1 Explicit join messages are sent to the switch, and a timeout determines when hosts leave a group.
IGMPv2 Adds a leave message to the join message, allowing the switch to easily determine when a group has no interested listeners on a connected LAN.
IGMPv3 Defined in RFC 3376. Supports a single source of content for a multicast group.

Global settings

Use the Global settings tab to turn IGMP snooping on or off.

To configure IGMP snooping, do as follows:

  1. For Status, select Turned on or Turned off to turn IGMP snooping on or off. The default setting is Turned off.

  2. For Report Suppression, enter the report suppression value. The report suppression feature limits the number of membership reports the member sends to multicast-capable routers. The default value is 5. The range is from 1 to 25.

  3. Click Apply.

VLAN settings

Use the IGMP snooping VLAN Settings to configure IGMP snooping settings for VLANs on the system. The switch performs IGMP snooping on VLANs that send IGMP packets. You can specify the VLANs on which IGMP snooping should be performed.

To configure IGMP snooping for VLANs, do as follows:

  1. Click Edit next to the VLAN you want to configure.
  2. Select On or Off for IGMP snooping status from the drop-down list.
  3. Select the Version from the drop-down list.
  4. Select On or Off for Fast leave.
  5. Click Apply.

If fast leave isn't used, a multicast querier will send a GS query message when an IGMPv2/v3 group leaves a received message. The querier only stops forwarding traffic for that group if no endpoint replies to the query within the specified timeout period. If fast leave is turned on, the switch considers the port to have only one endpoint attached. Therefore, you should only turn fast leave on for a port connected to just one IGMP-enabled device.

Fast leave is supported only with IGMPv2 or IGMPv3 snooping when IGMP snooping is turned on. Fast leave does not apply to a port if the switch has learned that a multicast querier is attached.

Fast leave can improve bandwidth usage for a network that frequently experiences many IGMP host add and leave requests.

Querier settings

IGMP snooping requires that one central switch periodically queries all endpoint devices on the network to confirm their multicast membership. This central device is the IGMP querier.

To configure querier settings, do as follows:

  1. Click Edit next to the VLAN you want to configure.
  2. For Querier status, select On or Off from the drop-down list.
  3. For Interval, enter the time in seconds between general query transmissions. The default is 125 seconds.
  4. For Maximum response interval, enter the maximum response time used in the queries the snooping querier sends. The default is 12 seconds.
  5. For Startup query counter, enter the number of Query Counter values. Query count adjusts the period between membership queries for a specified number of messages.

  6. For Startup query interval, enter the time of Query internal values. The query interval is the period in seconds between IGMP Membership Query message transmissions. The interval ranges from 5 to 3600 seconds.

  7. Click Apply.

Group list

The group list displays the VLAN ID, group IP address, and member ports in the IGMP snooping list.

Router settings

The router settings table shows the learned multicast router attached port if the port is active and a member of the VLAN. All IGMP packets snooped by the switch are forwarded to the multicast router that's reachable from the port.

Options Description
VLAN ID Displays the VLAN ID.
Dynamic Port List Displays router ports that are dynamically configured.
Static Port list Designates a range of ports connected to multicast-enabled routers. Ensures that all the packets will reach the multicast-enabled router.
Forbidden Port List Designates a range of ports as disconnected from multicast-enabled routers. Ensures that the forbidden router port won't propagate routing packets out.

To manually configure router settings, do as follows:

  1. Select the VLAN ID.
  2. Enter the Static port.
  3. Enter the Forbidden port.
  4. Click Apply.