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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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Basic Concepts

Basic Concepts

In Figure 4-2, the user-side device (switch or host) connects to SwitchA and SwitchB through M-LAG to constitute a dual-active system. SwitchA and SwitchB then forward traffic together to ensure network reliability.

Figure 4-2 Basic M-LAG topology
Table 4-1 describes basic concepts of M-LAG.
Table 4-1 Basic concepts of M-LAG



Dynamic Fabric Service (DFS) group

A DFS group is used for pairing between M-LAG devices. M-LAG devices use the DFS group protocol to synchronize information such as the interface status and entries.

DFS master device

The device is configured with M-LAG and is in master state. It is also called the M-LAG master device.

DFS backup device

The device is configured with M-LAG and is in backup state. It is also called the M-LAG backup device.


A DFS group consists of a master device and a backup device. Under normal circumstances, both the master and backup devices forward service traffic and their forwarding behaviors are the same. The master and backup devices have different forwarding behaviors only when a fault occurs.

Dual-Active Detection (DAD) link

A DAD link is used for M-LAG master and backup devices to exchange DAD packets at Layer 3.

Under normal circumstances, the DAD link does not participate in any traffic forwarding behaviors in the M-LAG. It is only used to detect whether two master devices exist when a fault occurs. The DAD link can be an external link, for example, if the M-LAG is connected to an IP network and the two member devices can communicate through the IP network, the link that enables communication between the member devices can function as the DAD link. An independent link that provides Layer 3 reachability can also be configured as the DAD link, for example, a link between management interfaces of the member devices can function as the DAD link.

Peer-link interface

Peer-link interfaces are at both ends of a peer-link.


A peer-link is between two directly connected devices and has link aggregation configured. It is used to exchange negotiation packets and transmit part of traffic. After an interface is configured as a peer-link interface, other services cannot be configured on the interface.

To improve the peer-link reliability, you are advised to use multiple links for aggregation.

M-LAG member interface

M-LAG member interfaces are the Eth-Trunks on M-LAG master and backup devices that are connected to the user-side host or switch.

To improve the reliability, you are advised to configure link aggregation in LACP mode.

M-LAG member interfaces also work in master/backup mode. When the local and remote member interfaces synchronize information, the interface that changes from Down to Up first becomes the master M-LAG member interface, and the other interface becomes the backup M-LAG member interface.

The master and backup M-LAG member interfaces have different forwarding behaviors only when the M-LAG forwards multicast traffic.
Updated: 2019-05-08

Document ID: EDOC1100004351

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