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[EX] When will current MAC address change in a Virtual Chassis



Article ID: KB17867 KB Last Updated: 03 Mar 2017Version: 2.0
When will current MAC address change in Virtual Chassis
A customer asked why the MAC address is not changing after they do a switchover. This article describes when the MAC address changes in a Virtual Chassis.

For information on the MAC address assignment, refer to KB17866 - EX Switch - MAC address assignment in a Virtual Chassis (VC).
A MAC address is selected as system MAC base for the virtual chassis. Initially the MAC address of the master is chosen as the system MAC base. Once chosen, it serves as the system MAC base for the virtual system, as long as the member which contains this MAC base is part of the VC in any role (Master, Backup, Linecard).

Once the member whose MAC address is being using as system MAC leaves the VC, the current master's MAC address is chosen as the new system MAC base and all interfaces are reconfigured with new MAC address.

Once the selection is over, the Master pushes the MAC address to all the members as they joined the VC. Every time a member leaves, the MAC persistence timer is started and when it expires, the Master checks if the MAC address belongs to VC; if not, it chooses its own MAC as system MAC and informs all the members.

The default MAC persistence Timer is set to 10 minutes, it can be changed by "set virtual-chassis mac-persistence-timer" commands as below:

lab@EX4200-24T# set virtual-chassis mac-persistence-timer ?
Possible completions:
<timer> MAC persistence time (minutes) <---
+ apply-groups Groups from which to inherit configuration data
+ apply-groups-except Don't inherit configuration data from these groups

The current MAC address in a Virtual Chassis system will be changed only under the following conditions:
  1. The member who has the system base MAC address leaves the VC AND
  2. More than 10 minutes (or the value set as mac-persistence-timer) has passed since the member is removed from the VC
After that, the new master's mac address will be selected as system MAC base address for the virtual chassis.

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