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Configuration Guide - Ethernet Switching

CloudEngine 8800, 7800, 6800, and 5800 V200R003C00

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, MUX VLAN, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, and Layer 2 protocol transparent transmission.
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Traffic Forwarding in M-LAG Failure Scenarios

Traffic Forwarding in M-LAG Failure Scenarios

M-LAG technology improves link reliability from card-level to device-level. If a fault (link, device, or peer-link fault) occurs, M-LAG ensures that normal services are not affected. The following describes how M-LAG ensures proper service running when a fault occurs.

Uplink Failure

Figure 4-13 Uplink failure

DAD packets are generally transmitted through the DAD link between management interfaces. Therefore, DAD between M-LAG master and backup devices is not affected when an uplink fails. The dual-active system is not affected, and M-LAG master and backup devices still properly forward traffic. In Figure 4-13, traffic passing the M-LAG master device is forwarded through the peer-link because the uplink of the M-LAG master device fails.

If the DAD link is on a service network and the faulty uplink is the DAD link, the M-LAG works properly without being affected. If the peer-link also fails, DAD cannot be performed and packet loss occurs.

Downlink Failure

Figure 4-14 Downlink failure

If a downstream M-LAG member interface fails, the DFS group master and backup states do not change. However, if the faulty M-LAG member interface is in master state, the backup M-LAG member interface changes to master state, and traffic is switched to the corresponding link for transmission. The link of the faulty M-LAG member interface goes Down, and the dual-homing networking changes to single-homing networking. The MAC address of the faulty M-LAG member interface is changed to that of the peer-link interface in corresponding entries. After the faulty M-LAG member interface recovers, the status of M-LAG member interfaces is not changed. The backup M-LAG member interface that changes to the master M-LAG member interface remains in master state, and the original master M-LAG member interface is in backup state after the fault is rectified. You can run the display dfs-group dfs-group-id node node-id m-lag command to view the status of an M-LAG member interface.

Assume that a multicast source is at the network side and a multicast group member is at the access side. If the M-LAG member interface on the M-LAG master device fails, the device instructs the remote device to update multicast entries through M-LAG synchronization packets. M-LAG master and backup devices do not load balance traffic depending on whether the last digit of the multicast group address is an odd or even number, and all multicast traffic is forwarded by the M-LAG backup device on which the M-LAG member interface is Up. If the M-LAG member interface on the M-LAG backup device fails, multicast traffic is forwarded similarly.

M-LAG Master Device Failure

Figure 4-15 M-LAG master device failure

If the M-LAG master device fails, the M-LAG backup device becomes the master device and continues to forward traffic, and its Eth-Trunk link is still in Up state. The Eth-Trunk link of the M-LAG master device goes Down, and the dual-homing networking changes to single-homing networking.

If the M-LAG backup device fails, the M-LAG master and backup status remains unchanged, and the Eth-Trunk link of the M-LAG backup device goes Down. The Eth-Trunk link of the M-LAG master device is still in Up state and continues to forward traffic. The dual-homing networking changes to single-homing networking.

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Updated: 2019-05-08

Document ID: EDOC1100004351

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