Alcatel-Lucent 6850-48 网络指南

Configuring MAC Retention

MAC Retention Overview

OmniSwitch AOS Release 6 Network Configuration Guide

page 18-3

A “stack element” or simply “element” is a switch that has designated stacking ports. The switches are 
operatively interconnected via these ports to form a virtual chassis referred to as a stack. Each element in a 
stack can be elected as the primary or the secondary element. The primary element is elected based on the 
highest uptime or the lowest slot number or the lowest base MAC address. The secondary element is 
elected based on the lowest slot number or the lowest base MAC address of the remaining elements in the 
stack.The system of stackable switches is generally coupled in a series and the topology of the system is 
generally characterized by a closed loop called a ring. A stackable switch is adapted to perform switching 
between its own data ports and between the data ports of other stackable switches by transmitting packets 
via the stacking ports.

Each stack element has a unique base MAC address. Generally, the stack address is the MAC address of 
the current primary element. When a primary element fails, a secondary element starts functioning as the 
new primary element. This is known as takeover. During takeover, the stack address is also accordingly 
changed to reflect the base MAC address of the new primary element.

Whenever a takeover occurs, it impacts not only the stack, but also the devices that communicate with that 
stack. 

The following diagram shows a stack connected to a stand-alone switch:

In the above diagram, Stack 1 has the stack address M1. When a takeover occurs, the secondary element 
starts functioning as the new primary element and the stack address is also changed, for example, to M2, 
the new primary element’s MAC address. Stack 1 advertises its new stack address M2. Switch 1, which