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Configuration Guide - IP Multicast

S7700 and S9700 V200R010C00

This document describes IP multicast basics and how to configure IP multicast features, including IGMP/MLD, PIM (IPv4&IPv6), MSDP, multicast VPN, Layer 3 multicast CAC, Layer 2 multicast CAC, IGMP/MLD snooping, and multicast VLAN, IPv4&IPv6 multicast route management, static multicast MAC address, multicast network.
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Layer 2 Multicast Packets Cannot Be Forwarded in a VLAN

Layer 2 Multicast Packets Cannot Be Forwarded in a VLAN

Fault Description

Multicast packets can be forwarded normally when IGMP snooping is not configured. However, users cannot receive multicast packets after IGMP snooping is configured.

Procedure

  1. Check whether the IGMP snooping version configured on the switch is earlier than that running on user hosts.

    If the IGMP snooping version configured on the switch is earlier than that running on user hosts, the switch only forwards IGMP Report messages to router ports and does not generate group member ports and forwarding entries.

    Run the display igmp-snooping configuration command to check the IGMP snooping configuration. If the IGMP snooping version configured on the switch is earlier than that running on user hosts, run the igmp-snooping version version command to set the IGMP snooping version to be the same as the IGMP version running on user hosts.

  2. Check whether the general query interval configured on the switch is the same as that configured on the upstream device.

    If the general query interval on the switch is smaller than the general query interval on the upstream IGMP querier or IGMP snooping device, the switch may mistakenly age out some IGMP snooping entries that are still in use. As a result, multicast packets matching these entries cannot be forwarded.

    Run the display igmp-snooping command to check IGMP snooping parameters. If the general query interval on the switch is smaller than the general query interval on the upstream IGMP querier or IGMP snooping device, run the igmp-snooping query-interval query-interval command to increase the IGMP snooping general query interval. It is recommended that the upstream and downstream devices use the same general query interval.

    On Huawei modular switches, the default values of the IGMP general query interval and IGMP snooping general query interval are both 60 seconds.

  3. Check whether router port dynamic learning is disabled.

    The switch does not listen to IGMP Query messages in a VLAN after router port dynamic learning is disabled in the VLAN.

    Run the display igmp-snooping configuration command to check whether router port dynamic learning is disabled. If the command output contains "undo igmp-snooping router-learning", run the igmp-snooping router-learning command to enable dynamic learning of router ports in the VLAN.

  4. Check whether fast leave of member ports is enabled.

    Configure fast leave in a VLAN only when each interface in the VLAN connects to only one host. If a member port is connected to multiple hosts and fast leave is enabled in the VLAN, the switch immediately deletes the forwarding entry of the member port after receiving an IGMP Leave message from the member port, and does not send a Group-Specific Query message. Therefore, multicast packets cannot be forwarded.

    Run the display igmp-snooping configuration command to check whether fast leave is enabled. If the command output contains "igmp-snooping prompt-leave", run the undo igmp-snooping prompt-leave command in the VLAN view to disable fast leave.

  5. Check whether the Router-Alert option is configured.

    If the Router-Alert option is configured, the switch checks the Option field of IGMP messages and discards messages without the Router-Alert option.

    Run the display igmp-snooping configuration command to check whether the Router-Alert option is configured. If the command output contains "igmp-snooping require-router-alert", run the undo igmp-snooping require-router-alert command in the VLAN view to delete the configuration.

  6. Check whether a multicast group policy is configured.

    The multicast group policy limits the multicast groups that hosts in a VLAN can join. Run the display igmp-snooping configuration command to verify the multicast group policy configuration. If an access control list (ACL) is configured, run the display acl command to verify the ACL configuration.

  7. Check whether Layer 2 multicast filtering is configured.

    If Layer 2 multicast filtering is configured on an interface, the interface discards the UDP packets from the specified VLAN.

    Run the undo multicast-source-deny command in the physical interface view to disable Layer 2 multicast filtering.

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Updated: 2019-08-21

Document ID: EDOC1000141903

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