How is convergence performance of Layer 2 multicast accelerated on an S series switch?


When the network topology changes, Layer 2 multicast detects the topology change by responding to notification messages of ring network protocols. Layer 2 multicast sends General Query messages in the VLAN where the topology changes to re-collect group member relationships. Ring network protocols include STP, MSTP, RRPP, Smart Link, and SEP. The ring network protocols supported by the switches excluding the S1700 are as follows:
- STP: supported by all switch models
- MSTP: supported by all switch models excluding the S2700SI
- RRPP: supported by all switch models excluding the S1720 and S2700SI
- Smart Link: supported by all switch models excluding the S1720, S2700SI, S2710SI, and S2700EI
- SEP: supported by all switch models excluding the S1720, S2700SI, S2710SI, and S2700EI

Other related questions:
Configure an S series switch to accelerate OSPF route convergence
The following network changes affect OSPF route convergence. A device detects that the peer link is down and the neighbor relationship becomes invalid. A new link-state advertisement (LSA) is generated and flooded. The Link State Database (LSDB) is updated. A new route is calculated through the Shortest Path First (SPF) routing algorithm and delivered to the Forwarding Information Base (FIB) table. To accelerate OSPF aggregation, you can perform the following operations on a switch: Set a Hello interval and a Dead interval on the peer device or configure the BFD to rapidly detect failures. Set spf-schedule-interval (of which the default value is 5, in seconds) to a smaller value to shorten the SPF calculation interval. Set the LSA generation interval to a smaller value. Set the LSA arrival check interval to a smaller value. Run the ospf trans-delay command in an interface view to speed up LSA flooding.

Difference between forwarding modes of Layer 2 multicast on an S series switch
After Layer 2 multicast is enabled on an S series switch, the switch maintains a Layer 2 multicast forwarding table. When receiving a multicast packet, the switch matches the multicast address of the packet with multicast forwarding entries to determine the outbound interface. Whether the switch determines the outbound interface based on the multicast IP address or multicast MAC address depends on the configured Layer 2 multicast forwarding mode. Multiple multicast IP addresses may be mapped to one MAC address. If multicast data is forwarded based on the MAC address, multicast data may be sent to the users who do not order the multicast data. MAC address-based multicast forwarding can improve specifications in certain scenarios. Different models support different Layer 2 multicast forwarding modes: - The S1720, S2700SI, S2710SI, S2700EI, S2720, S2750EI, S5700S-LI, and S5700LI support only MAC address-based multicast forwarding. - The S3700SI and S5710-C-LI support only IP address-based multicast forwarding. - The S5700SI supports only IP address-based multicast forwarding in V200R002 and earlier versions, and supports MAC address-based and IP address-based forwarding modes starting from V200R003. - The S3700EI, S3700HI, S5710-X-LI, S5720S-SI, S5720SI, S5700EI, S5710EI, S5720EI, S5700HI, S5710HI, S5720HI, S6700EI, S6720EI, S7700, S9700, S12700, S9300, and E600 support MAC address-based and IP address-based forwarding modes.

Layer 2 multicast entries and usage of S series switches
For an S series switch, entries fall into protocol and forwarding entries. Protocol entries include router port entries and host port entries. You can run the display igmp-snooping router-port command to check router port entries, run the display igmp-snooping port-info command to check host port entries, and run the display l2-multicast forwarding-table command to check forwarding entries. Protocol entries are triggered by protocol packets or manually generated. They are used to identify the protocol exchange status. Forwarding entries are generated based on protocol entries and are used to guide subsequent multicast data forwarding.

Default Layer 2 multicast forwarding mode on an S series switch
For S series switches excluding the S1700, after Layer 2 multicast is enabled, the S1720, S2710SI, S2700SI, S2700EI, S2720EI, S2750EI, S5700LI, and S5700S-LI (S5700S-28X-LI-AC and S5700S-52X-LI-AC) forward multicast data based on MAC addresses, and other models forward multicast data based on IP addresses by default.

How to configure Layer 2 multicast on a CE series switch

When a CE series switch functions as a Layer 2 switch, it broadcasts all multicast packets passing through it in a broadcast domain by default. Therefore, all hosts in the same broadcast domain receive the multicast packets, regardless of whether they are group members. This causes a waste of network bandwidth and brings security risks.

This problem can be solved by configuring IGMP snooping on the Layer 2 multicast switch. After IGMP snooping is configured, the Layer 2 multicast switch listens to and analyzes IGMP packets exchanged between multicast users and the upstream router, and creates Layer 2 multicast forwarding entries accordingly. Multicast data packets are then forwarded based on the Layer 2 multicast forwarding entries, instead of being broadcast on the Layer 2 network.

# Configure IGMP snooping in VLAN 10.

<HUAWEI> system-view
[~HUAWEI] igmp snooping enable   //Enable IGMP snooping globally.
[*HUAWEI] vlan 10
[*HUAWEI-vlan10] igmp snooping enable   //Enable IGMP snooping in a VLAN (broadcast domain).
[*HUAWEI-vlan10] commit

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