How to configure MAC-Delay on Omada S6500 and S7500 series switches

Contents

Introduction

Requirements

Configuration

Verification

Conclusion

Introduction

In a stacked network topology, the stacking system operates as a single logical device when interfacing with other network devices; a single MAC address will be designated as the MAC address for this stacking system. On Omada switches, when the stacking system is formed for the first time, this address is the master unit's MAC address; it will then change following the related rules and may not be the same as the current master’s MAC address. Without MAC-Delay, the system will instantaneously reassign the MAC address to that of the newly elected master following a master unit failure or its removal from the stack. Such rapid transitions can precipitate protocol instability, including reconvergence flapping in mechanisms like LACP and STP, thereby potentially disrupting network availability and business-critical services.

As mentioned above, the whole stacking system will use the MAC address of the master unit as its MAC address when the stacking system is formed for the first time. Based on this, MAC-Delay configuration on Omada switches gives you three options when the master unit or the unit providing the MAC address is down or removed from the stacking system:

• Disable MAC-Delay: When the master unit or the unit providing the MAC address is down or removed from the stacking system, the system’s MAC address will immediately be changed to the new master’s MAC address.
• Configure a time span for MAC-Delay: When the master unit or the unit providing MAC address is down or removed from the stacking system, the system’s MAC address will remain unchanged within this time span, which range configurable is 1-60 minutes, if the previous unit providing MAC address doesn’t return to the stacking system after the time span configured, the stacking system’s MAC address will be changed to the new master’s MAC address.
• Configure a 0 time span for MAC-Delay: Setting the MAC-Delay time span to 0 prevents the stacking system’s MAC address from changing. As a result, even if the previous unit providing the MAC address returns to this stacking system, the system’s MAC address will remain unchanged.

Requirements

• Omada S6500 and S7500 series Switches

Configuration

The following part will show the difference between the three options of MAC-Delay after the switches are stacked. We will stack two switches together and configure different MAC-Delay options to demonstrate the difference when the master unit leaves the stacking system and returns after a period.

The following example will be given using an S6500-24GP4XF and an S6500-24G4XF.

Step 1. Stack the switches. For both switches, use port 25 as the stacking port. Commands as follows:

For S6500-24GP4XF:

switch 1 stack-group 1
interface 1/0/25
exit

For S6500-24GP4XF:

switch 1 stack-group 1
interface 1/0/25
exit

Currently, the two switches’ port 25 are configured as stacking ports and are ready for stacking. To initiate the stacking process, connect the cable between the two ports. The stacking process will then automatically start, and you should wait for it to complete.

Step 2. Configure MAC-Delay. After the switches are stacked, go to the master unit’s CLI, in global config view, use the following commands to configure:

• To disable MAC-Delay: switch mac-delay immediately
• To set a time span (1-60 minutes) for MAC-Delay: switch mac-delay <1-60>
• To set 0 time span for MAC-Delay (Never change MAC): switch mac-delay 0

We have completed the configuration for MAC-Delay.

Verification

After the switches are stacked, use the command “show switch” to check the stacking units info, master/member status, and the current MAC address of the stacking system. In this example, S6500-24G4XF is the master, S6500-24GP4XF is the member, and the current MAC address of the stacking system is the same as that of S6500-24G4XF.

In standalone mode by default, MAC-Delay is enabled with 10 minutes. Use the command “switch mac-delay show” to check the status of the MAC-Delay set.

If MAC-Delay is configured as disabled, the MAC address will change immediately when the master unit leaves the stacking system. We could unplug the master unit’s power to emulate this scenario, then immediately enter the member unit’s CLI to check the stacking system status. When the stacking system is operating normally, the “show switch” result on the member unit is:

Shutdown master unit, wait for the stacking system to become stable, recheck the info:

After the stacking system stabilized, S6500-24GP4XF immediately changed from member to master, and the stacking system MAC address also changed immediately. There is also a log during the reorganization of the stacking system:

In case of MAC-Delay configured for a time span, for the convenience of example config, here we configure the time span as 2 minutes and validate, during the regular operation of the stacking system, the “show switch” result on the member unit is:

The stacking system MAC address is the same as that of the master unit. We now shut down the master unit and check on the member unit immediately after the system stabilizes:

The stacking system MAC address remains unchanged for now, which is different from the current master. There are also logs indicating the stacking system MAC remains unchanged during the re-organization and changes when the time span passes:

Now, recheck the stacking system status, we can see that the system MAC has changed to be the same as that of the master unit:

If MAC-Delay is configured for 0 time span, the stacking system's MAC address will never change. During the regular operation of the stacking system, the “show switch” result on the member unit is:

The stacking system MAC address is the same as that of the master unit. We now shut down the master unit and check on the member unit immediately after the system stabilizes:

The MAC address of the stacking system remains unchanged, differing from the current master unit. Also, no logs are indicating a MAC address change; this MAC address will be kept forever on the stacking system.

Conclusion

In this article, we introduced what MAC-Delay is and the different configurations of MAC-Delay on Omada switches.

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