Cisco Firepower 4100 Command Reference

set prefix
To set the MAC address prefix to use when autogenerating MAC addresses for container instance interfaces,
use the set prefix command.
set prefix prefix
Syntax Description
Specifies a decimal value between 1 and 65535. This prefix is converted to a
four-digit hexadecimal number, and used as part of the MAC address.
prefix
Command Modes
scope ssa/scope auto-macpool/
Command History
ModificationRelease
Command added.2.4(1)
Usage Guidelines
The FXOS chassis automatically generates MAC addresses for container instance interfaces, and guarantees
that a shared interface in each instance uses a unique MAC address.
If you manually assign a MAC address to a shared interface within the application, then the manually-assigned
MAC address is used. If you later remove the manual MAC address, the autogenerated address is used. In the
rare circumstance that the generated MAC address conflicts with another private MAC address in your network,
we suggest that you manually set the MAC address for the interface within the application.
Because autogenerated addresses start with A2, you should not start manual MAC addresses with A2 due to
the risk of overlapping addresses.
Even if you are not sharing a subinterface, if you manually configure MAC addresses, make sure you use
unique MAC addresses for all subinterfaces on the same parent interface to ensure proper classification.
Note
The FXOS chassis generates the MAC address using the following format:
A2xx.yyzz.zzzz
Where xx.yy is a user-defined prefix or a system-defined prefix, and zz.zzzz is an internal counter generated
by the chassis. The system-defined prefix matches the lower 2 bytes of the first MAC address in the burned-in
MAC address pool that is programmed into the IDPROM. Use connect fxos, then show module to view the
MAC address pool. For example, if the range of MAC addresses shown for module 1 is b0aa.772f.f0b0 to
b0aa.772f.f0bf, then the system prefix will be f0b0.
The user-defined prefix is an integer that is converted into hexadecimal. For an example of how the user-defined
prefix is used, if you set a prefix of 77, then the chassis converts 77 into the hexadecimal value 004D (yyxx).
When used in the MAC address, the prefix is reversed (xxyy) to match the chassis native form:
A24D.00zz.zzzz
For a prefix of 1009 (03F1), the MAC address is:
A2F1.03zz.zzzz
Cisco Firepower 4100/9300 FXOS Command Reference
213
S Commands
set prefix

Cisco Firepower 4100 Specifications

General

Brand	Cisco
Model	Firepower 4100
Category	Firewall
Language	English