Use of MAC Addresses in Firepower Interface Settings

You can manually configure Media Access Control (MAC) addresses to override the default value.

For a high availability configuration, you can configure both the active and standby MAC address for an interface. If the active unit fails over and the standby unit becomes active, the new active unit starts using the active MAC addresses to minimize network disruption.

Active and standby MAC addresses are configured on the Advanced tab when configuring an interface.

Default MAC Addresses

Default MAC address assignments depend on the type of interface.

Physical interfaces - The physical interface uses the burned-in MAC address.
Subinterfaces - All subinterfaces of a physical interface use the same burned-in MAC address. You might want to assign unique MAC addresses to subinterfaces. For example, your service provider might perform access control based on the MAC address. Also, because IPv6 link-local addresses are generated based on the MAC address, assigning unique MAC addresses to subinterfaces allows for unique IPv6 link-local addresses.