32.5 Notes on using IGMP snooping/MLD snooping

(1) Coexistence with other functions

[See "24.3 Coexistence of Layer 2 Switch Function and Other Functions"

(2) Control packet flooding

Because multicast traffic that is subject to suppression by IGMP snooping or MLD snooping is data traffic, flooding needs to be performed within a VLAN so that the routing protocol and other control packets can be received by all routers and all hosts. Therefore, the Switch forwards packets with destination IP addresses contained in the address ranges shown in the table below to all ports on the VLAN. Packets with destination IP addresses outside the address ranges shown in the following table are forwarded according to learning results for IGMP snooping or MLD snooping.

Note that multicast group addresses that duplicate multicast MAC addresses for control packets cannot be used. The following table describes multicast group addresses that cannot be used for addresses outside the address ranges shown in the above table.

When addresses shown in the above table are used for multicast group addresses, multicast data bound for corresponding multicast group addresses will be forwarded to all ports in the VLAN.

When setting a trunk port, make sure that it does not receive any untagged control packets. Set a native VLAN in the configuration if untagged control packets are to be handled by the trunk port.

(3) Configuring Multicast Router Ports

(4) Auto-learning of multicast router ports

(5) Connecting to IGMP Version 3 Hosts

When connecting IGMPv3 to the Switch, the following actions are required.

• Set an IP address so that the corresponding router connected to the IGMPv3 router becomes the representative querier.

Use a configuration in which IGMPv3 messages from IGMPv3 hosts are not split into fragments.

(6) Connecting with MLD Version 2 Hosts

When connecting MLDv2 to the Switch, the following actions are required.

• Set an IP address so that the corresponding router connected to the MLDv2 router becomes the representative querier.

Use a configuration in which IGMPv2 messages from IGMPv2 hosts are not split into fragments.

(7) Re-learning entries by executing an operation command

In addition to the operation commands for IGMP and MLD snooping, if the commands below are executed, any learned entries are cleared and then relearned. After these operation commands are executed, multicast communication will be cut off temporarily.

• The running-config command is overwritten by the copy command

• Executing the restart vlan command

(8) IGMP Fast-Leave Function

When IGMP instant leave is used and an IGMPv2 Leave or IGMPv3 Report (leave request) message is received, multicast communication to the corresponding port stops immediately. Therefore, when this functionality is used, we recommend that you place only one recipient terminal for each multicast group on the connection port.

When multiple recipient terminals in the same multicast group are placed on a connection port, multicast communication to other recipients stops temporarily. In this case, multicast communication is restarted when an IGMP Report (membership request) message is received from the recipient.

(9) IGMP Query messaging interval

• When operating in IGMPv2, set the sending interval for IGMP Query messaging to the same value in the applicable VLAN including other devices.

• If the interval for sending Query messages is less than 10 seconds, the bursting rate of Report messages sent from multicast group receivers increases, which may cause Report messages to be lost on the Switch. For this reason, set the sending interval of Query messages so that the total number of Report messages to be returned x 1/10 is 100 or less.

(10) Using IGMP snooping in a Stacked Configuration

The following notes apply to using this function in a stack configuration:

• When using IGMP querier function

  Set the networking Query interval to 30 seconds or longer. If it is used in less than 30 seconds, multicast communication may stop when the master is switched.

• When IGMP querier function is not used

  Use a networking Query interval between 30 and 125 seconds. If it is used for more than 125 seconds or less than 30 seconds, multicast communication may stop during master switching.