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Cisco Defense Orchestrator

Configure Advanced Firepower Interface Options

Advanced interface options have default settings that are appropriate for most networks. Configure them only if you are resolving networking problems.

The following procedure assumes the interface is already defined. You can also edit these settings while initially editing or creating the interface.

This procedure and all of the steps in it are optional. 


  • You cannot set MTU, duplex, or speed for the Management interface on a Firepower 2100 series device.
  • The MTU of an unnamed interface must be set to 1500 bytes.


  1. On the Devices & Services page, click the device whose interfaces you want to configure and click Interfaces in the Management pane at the right.
  2. On the Interfaces page, select the physical interface you want to configure and in the Actions pane at the right, click Edit
  3. Click the Advanced tab. 
  4. Enable for HA Monitoring is automatically enabled. When this is enabled, the device includes the health of the interface as a factor when the HA pair decides whether to fail over to the peer unit in a high availability configuration.
    This option is ignored if you do not configure high availability. It is also ignored if you do not configure a name for the interface.
  5. To make a data interface management only, check Management Only .

A management only interface does not allow through traffic, so there is very little value in setting a data interface as a management only interface. You cannot change this setting for the Management/Diagnostic interface, which is always management only.

  1. Modify the IPv6 DHCP configuration settings.
  • Enable DHCP for IPv6 address configuration —Whether to set the Managed Address Configuration flag in the IPv6 router advertisement packet. This flag informs IPv6 autoconfiguration clients that they should use DHCPv6 to obtain addresses, in addition to the derived stateless autoconfiguration address.
  • Enable DHCP for IPv6 non-address configuration —Whether to set the Other Address Configuration flag in the IPv6 router advertisement packet. This flag informs IPv6 autoconfiguration clients that they should use DHCPv6 to obtain additional information from DHCPv6, such as the DNS server address.
  1. Configure DAD Attempts —How often the interface performs Duplicate Address Detection (DAD), from 0 - 600. The default is 1. During the stateless auto configuration process, DAD verifies the uniqueness of new unicast IPv6 addresses before the addresses are assigned to interfaces. If the duplicate address is the link-local address of the interface, the processing of IPv6 packets is disabled on the interface. If the duplicate address is a global address, the address is not used. The interface uses neighbor solicitation messages to perform Duplicate Address Detection. Set the value to 0 to disable duplicate address detection (DAD) processing.
  2. Change the MTU  (maximum transmission unit) to the desired value.

The default MTU is 1500 bytes. You can specify a value from 64 - 9198 (or 9000, for Firepower Threat Defense Virtual). Set a high value if you typically see jumbo frames on your network. See MTU Settings in Interfaces for more information.

Note: If you increase MTU above 1500 on ASA 5500-X series devices, ISA 3000 series devices, or Firepower Threat Defense Virtual, you must reboot the device. Log into the CLI and use the reboot command. You do not need to reboot Firepower 2100 series devices, where jumbo frame support is always enabled.

  1. (Physical interface only.) Modify the speed and duplex settings.

The default is that the interface negotiates the best duplex and speed with the interface at the other end of the wire, but you can force a specific duplex or speed if necessary. The options listed are only those supported by the interface. Before setting these options for interfaces on a network module, please read Limitations for Interface Configuration.

  • Duplex— Choose Auto, Half, Full, or Default. Auto is the default when the interface supports it. For example, you cannot select Auto for the SFP interfaces on a Firepower 2100 series device. Select Default to indicate that Firepower Device Manager should not attempt to configure the setting. If Duplex is set to Auto, Speed must also be set to Auto.

Any existing configuration is left unchanged.

  • Speed— Choose Auto to have the interface negotiate the speed (this is the default), or pick a specific speed: 10 , 100, 1000, 10000 Mbps. If Speed is set to Auto, Duplex must also be set to Auto. You can also select these special options:

Any existing configuration is left unchanged.

The type of interface limits the options you can select. For example, the SFP+ interfaces on a Firepower 2100 series device support 1000 (1 Gbps) and 10000 (10 Gpbs) only, and the SFP interfaces support 1000 (1 Gbps) only, whereas GigabitEthernet ports do not support 10000 (10 Gpbs). SPF interfaces on other devices might require No Negotiate . Consult the hardware documentation for information on what the interfaces support.

  1. (Optional, recommended for subinterfaces and high availability units.) Configure the MAC address.

By default, the system uses the MAC address burned into the network interface card (NIC) for the interface. Thus, all subinterfaces on an interface use the same MAC address, so you might want to create unique addresses per subinterface. Manually configured active/standby MAC addresses are also recommended if you configure high availability. Defining the MAC addresses helps maintain consistency in the network in the event of failover.

MAC Address—The Media Access Control in H.H.H format, where H is a 16-bit hexadecimal digit. For example, you would enter the MAC address 00-0C-F1-42-4C-DE as 000C.F142.4CDE. The MAC address must not have the multicast bit set, that is, the second hexadecimal digit from the left cannot be an odd number.)

Standby MAC Address—For use with high availability. 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, while the old active unit uses the standby address.

  1. Click Create.