After setting the interface mode to inline and enabling the interfaces on a Cisco Secure Firewall Threat Defense (FTD) device in an inline IPS deployment, the next step is to configure an inline set. An inline set groups two interfaces that work together to inspect traffic passing between them.
Steps to configure an inline set:
* In FMC, navigate to Devices > Device Management.
* Select the FTD device and configure the interfaces.
* Create a new inline set, adding the relevant interfaces that have been set to inline mode.
* Deploy the configuration to the FTD device.
Configuring an inline set ensures that the traffic between the specified interfaces is inspected and processed according to the IPS policies, completing the implementation of the inline IPS deployment.
References: Cisco Secure Firewall Management Center Configuration Guide, Chapter on Inline Sets.

In a failover configuration with Cisco Secure Firewall Threat Defense (FTD) devices, ensuring that users on the internal network can continue to communicate with outside devices if the primary device (FTD1) fails requires the implementation of a stateful failover link. The stateful failover link allows the secondary device (FTD2) to maintain session information and state data, ensuring seamless failover and minimizing disruptions.
Steps to implement a stateful failover link:
* Physically connect a stateful failover link between FTD1 and FTD2.
* Configure the stateful failover link in the FMC.
* Ensure that both devices are properly synchronized and that stateful failover is enabled.
* Deploy the changes to both FTD devices.
By configuring a stateful link, the secondary FTD can take over active sessions without requiring users to re- establish their connections, thus ensuring continuous communication.
References:Cisco Secure Firewall Threat Defense Configuration Guide, Chapter on Failover Configuration.

Explanation:
The correct sequence of actions for configuring a multi-instance environment for high availability on a Cisco Firepower 4100 appliance is as follows:
* Add a resource profile for container instances. A resource profile defines the CPU, RAM, and disk space allocation for each container instance.You can create multiple resource profiles with different resource settings and assign them to different container instances1.
* Add a MAC pool prefix and view the MAC address for the container instance interfaces. A MAC pool prefix is a 24-bit prefix that is used to generate MAC addresses for the container instance interfaces.
You can specify a custom MAC pool prefix or use the default one.You can also view the MAC addresses that are assigned to each container instance interface1.
* Configure interfaces. You need to configure the physical interfaces, EtherChannels, and VLAN subinterfaces that will be used by the container instances.You can also configure shared interfaces that can be used by multiple container instances on the same security module/engine1.
* Add a Standalone Firepower Threat Defense for Cisco Secure Firewall Management Center. You need to add a logical device that runs a standalone Firepower ThreatDefense (FTD) application instance and register it with the Cisco Secure Firewall Management Center (FMC).This logical device will act as the management interface for the container instances1.
* Add a high-availability pair. You need to add another logical device that runs a standalone FTD application instance and register it with the FMC as well. Then, you need to configure high availability (HA) between the two standalone FTD logical devices.This will enable HA for the container instances that are associated with them1.