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Configuration Guide - Device Management

S1720, S2700, S5700, and S6720 V200R011C10

This document describes the principles and configurations of the Device Management features, and provides configuration examples of these features.
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Stack Setup

Stack Setup

A stack is set up after the following stages:
  1. Physical connection setup: When multiple switches are connected in a specific topology using an appropriate method based on network requirements, a stack network is established.
  2. Master election: Member switches exchange stack competition packets and elect a master switch according to master election rules.
  3. Topology information collection and standby switch election: The master switch collects topology information from all the member switches and assigns stack IDs to the member switches. Then a standby switch is elected.
  4. Running: The master switch synchronizes the topology of the stack to all the member switches, and member switches synchronize their system software and configuration files with the master switch. After that, the stack runs stably.

Physical Connection Setup

Member switches can be connected to form a stack using stack cards or service ports. For details about the two stack connection methods, see Stack Connection Modes. No matter which connection method is used, member switches can be connected in a chain or ring topology, as shown in Figure 9-4. Table 9-1 compares the two stack topologies in terms of reliability, link bandwidth utilization, and convenience of cable connections.
Figure 9-4  Stack topologies
Table 9-1  Comparison of stack topologies

Topology

Advantage

Disadvantage

Usage Scenario

Chain topology

Applicable for long-distance stacking because the first and last member switches do not need to be connected by a physical link.

  • Low reliability: If any stack link fails, the stack splits.

  • Low stack link utilization: The entire stack relies on a single path.

A chain topology is recommended when member devices are far from one another and a ring topology is difficult to deploy.

Ring topology

  • High reliability: If a stack link fails, the topology changes from ring to chain, and the stack can still function normally.

  • High link bandwidth efficiency: Data can be forwarded along the shortest path.

The first and last member switches need to be connected by a physical link, so this topology is not appropriate for long-distance stacking.

A ring topology is recommended when member switches are located near one another, because this topology has higher reliability and link utilization.

Master Election

Determine the stack connection mode and topology, connect the member switches with physical links, and then power on all member switches. These member switches elect the master switch, which manages the stack. The master switch is elected based on the following rules (the election ends when a winning switch is found):

  1. The switch that starts first becomes the master switch.

    The master election timeout interval is 20 seconds. The startup process may take different lengths of time on different member switches. When stack member switches are powered on or restart, some member switches may not participate in the first master election. When a switch that starts later joins the stack, the master switch is elected again. If the previous master switch fails the election, it restarts and then joins the stack as a non-master switch. If the switch that starts later fails the election, it can join the stack only as a non-master switch. For details, see Joining and Leaving a Stack. If you want a specific switch to act as the master switch, power on that switch first, and power on the other switches after this switch starts.
    NOTE:

    To ensure that master election is completed at a time, you are advised to use switches of the same model to set up a stack. If you want to set up a stack of different switch models, you are advised to connect switches of the same model together.

    For example, three switches A, B, and C set up a stack in a chain topology.
    • If A and B start first and C starts later, C joins the stack only as a non-master switch.
    • If A and C start first and become the master switches, A and C compete to be the master switch based on their startup time when B starts and joins the stack. The switch that fails the election restarts and joins the stack as a non-master switch.
    For example, four switches A, B, C, and D set up a stack in ring topology:
    • If A and B start first and C and D start later, C and D join the stack only as non-master switches.
    • If A and C start first and become the master switches, A and C compete to be the master switch based on their startup time when B and D start and join the stack. The switch that fails the election restarts and joins the stack as a non-master switch.
  2. If multiple switches complete startup at the same time, the switch with the highest stack priority becomes the master switch.

  3. If multiple switches complete startup at the same time and have the same stack priority, the switch with the smallest MAC address becomes the master switch.

Stack ID Assign and Standby Switch Election

After the master switch is elected, it collects topology information from member switches. Based on the information, the master switch calculates forwarding entries, and sends the calculated information to member switches. The master switch also assigns a stack ID to every member switch. The standby switch is elected to operate as a backup for the master switch. The first switch that completes startup after the master switch becomes the standby switch. If multiple switches complete the startup at the same time, the standby switch is elected according to the following rules:
  1. The switch with the highest stack priority becomes the standby switch.
  2. If the switches have the same stack priority, the one with the smallest MAC address becomes the standby switch.

The election ends when a winning switch is found. After the standby switch is elected, all the other member switches join the stack as slave switches.

Running

After role election and topology information collection are complete, all the member switches synchronize their system software and configuration files with the master switch.
  • Automatic software loading: Member switches can run different software versions. If different software versions running on the member switches are compatible with one another, the member switches can set up a stack. If the software version running on the master switch is different from those on the standby switch and slave switches, these switches download the system software from the master switch. Then, they restart with the new system software and rejoin the stack.

  • Configuration file synchronization: The standby switch and slave switches can download the configuration file of the master switch and apply this configuration file. This mechanism enables member switches to work like a single device and ensures that other switches continue working normally if the master switch fails.

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Updated: 2019-10-21

Document ID: EDOC1000178167

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