How does an S series switch process IGMP messages of a later version


If the version of a received IGMP message is later than the IGMP snooping version configured on the switch, the switch processes the IGMP message as follows:

- If the received message is a Report message, the switch forwards the message only to router ports and does not generate a member port or forwarding entry.
- If the received message is a Query message, the switch broadcasts the message in the VLAN and sets the receiving port as a router port.
After the multicast VLAN service is configured, IGMP messages are replicated and broadcast in user VLANs. If the switch receives many Group-Specific Query messages of a later version, the CPU usage may become high.

If IGMP messages of a later version degrade service performance on the switch, change the IGMP snooping version to the later version.

Other related questions:
IGMP versions available on S series switch
S series switches support three IGMP versions: IGMPv1, IGMPv2, and IGMPv3.

What is the difference between IGMP versions of S series switches
IGMP runs on the last-hop router to collect users' requests for programs. The requested multicast data is then sent from the multicast source to users through PIM. IGMP has three versions. 1. IGMPv1 IGMPv1 defines the General Query message and Report message. A user sends Report message to request a program. After the last-hop router receives the Report message, it adds the user to the specified multicast group and sends General Query messages at intervals to maintain the membership of the user. If the router does not receive any Report message from the user within two intervals, it considers that the user does not require the multicast data and deletes the user from the multicast group. 2. IGMPv2 In IGMPv1, if a user does not require data of a multicast group, it leaves the multicast group after two intervals for sending General Query messages. Multicast data is still sent to the user in this period, wasting bandwidth. IGMPv2 improves IGMPv1 by adding two types of messages: Leave message and Special Query message. When a user does not require data of a multicast group, the user sends a Leave message to the last-hop router. When a port of the router receives the Leave message, the router sends some Group-Specific Query messages (the quantity is specified by the robustness variable) to the interface to check whether other users in the broadcast domain on the interface require data of the multicast group. If another user requires data of the multicast group, the user replies with a Report message. When receiving the Report message, the router retains the interface. If no Report message is received, the router deletes the interface from the multicast forwarding entry. IGMPv2 is the most widely used one on networks. 3. IGMPv3 IGMPv1 and IGMPv2 messages contain only the multicast group addresses of the requested programs. If multiple multicast sources provide data with the same multicast group address, data of all the groups is transmitted to users. Users may not see the programs they request. IGMPv3 solves this problem. IGMPv3 adds a source list in the Report message and supports the following six types of source lists: -Include: accepts data provided by the multicast sources in the list. -Exclude: rejects the multicast group data provided by all sources in the list. -ChangeToInclude: starts to accept multicast group data provided by the multicast sources in the list (previously rejects the data). -ChangeToExclude: starts to reject multicast group data provided by the multicast sources in the list (previously accepts the data). -AllowNew: adds a source of which the data is accepted or rejected. -BlockOld: deletes previous sources of which the data is accepted or rejected. IGMPv3 replaces the Leave message with the Rep ort message and adds the Group-and-Source-Specific Query message.

How does an S series switch elect an IGMP querier
When a host subnet is connected to the interfaces on multiple devices, to avoid data conflict, only one interface is allowed to send Query messages. This interface is the querier. The other interfaces running IGMP can receive the IGMP messages in this subnet. In IGMPv1, the querier is elected by a multicast routing protocol such as PIM. In IGMPv2 and IGMPv3, the switch interface with the lowest IP address acts as the querier.

How IGMP messages are transparently transmitted on an S series switch enabled with IGMP snooping
After global IGMP snooping is enabled on a switch, the switch sends all the IGMP messages received from a VLAN to the CPU for processing. If the multicast service is not configured in a VLAN and the switch needs to directly forward the IGMP messages of this VLAN without sending them to the CPU, run the protocol-transparent command in the VLAN view to enable transparent transmission of protocol packets. S series fixed switches support transparent transmission of protocol packets starting from V200R001, and only the S3700HI, S5710EI, S5720EI, S5700HI, S5710HI, S5720HI, S6700EI, andS6720EI support this function. S series modular switches support this function.

Can S series switches use SSM mapping to convert the version of IGMP messages
Although SSM mapping takes effect only for IGMPv3 messages in a VLAN, the switch does not convert IGMPv2 messages into IGMPv3 messages before sending the messages to router ports. You can configure IGMP snooping proxy or IGMP snooping Report suppression on the switch to enable the switch to send IGMPv3 messages to the upstream device.

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