Contents

Issue

After moving several sub-interfaces to physical interfaces on Firewall Threat Defense (FTD) 1140 HA pairs, the monitor-interface commands that were previously visible in the output of show run command output are no longer displayed in the standard configuration view. The commands now only appear when using show run all command output. This change occurred even for interfaces that were not modified during the migration.

Our original interfaces were:

- E1/1 net1

- E1/2.1 net2

- E1/2.2 net3

- E1/2.3 net4

- E1/2.4 inside

The new interface layout is:

- E1/1 net1

- E1/2.4 inside

- E1/3 net2

- E1/4 net3

- E1/5 net4

Prior to the interface changes, the monitor-interface commands appeared in the standard show run command output:

device# show running-config | include monitor-interface

monitor-interface net1

monitor-interface net2

monitor-interface net3

monitor-interface net4

monitor-interface inside

no monitor-interface service-module

After moving from sub-interfaces to physical interfaces, the show run command output only displays a subset of the monitor-interface commands:

device# show running-config | include monitor-interface

monitor-interface inside

no monitor-interface service-module

However, all monitor-interface commands are visible when running show run all command:

device# show running-config all | include monitor-interface

monitor-interface net1

monitor-interface net2

monitor-interface net3

monitor-interface net4

monitor-interface inside

no monitor-interface service-module

This behavior change has impacted compliance monitoring policies that rely on the monitor-interface commands being visible in the standard show run command output.

Environment

- Cisco Firewall Threat Defense (FTD) 1140 appliances in High Availability (HA) configuration. Other hardware platforms can be also affected.

- FTD Software Version: 7.6.4. Other software versions can be also affected.

- Configuration change from sub-interfaces to physical interfaces performed.

Resolution

This behavior is expected and does not indicate a malfunction or software defect. When interfaces are changed from sub-interfaces to physical interfaces, the default monitor-interface behavior changes, and commands that match the default configuration are not explicitly displayed in the standard show run command output. The monitor-interface commands are still active and functional, but they are now considered default configurations for physical interfaces. Default configurations are only visible when using the show run all command output, which displays both explicit and default configurations.

Verification Steps

To verify that monitor-interface functionality is still active, use these commands.

Step 1: Check standard configuration display:

device# show running-config | include monitor-interface

Step 2: Check complete configuration including defaults:

device# show running-config all | include monitor-interface

Step 3: Verify failover monitoring status:

device# show failover

Step 4: To display information about the interfaces monitored for failover:

device# show monitor-interface

The difference in output between show run and show run all command outputs confirms that the monitor-interface commands are functioning as default configurations rather than explicit configurations.

Cause

- When interfaces are migrated from sub-interfaces to physical interfaces, the FTD system applies different default behaviors for monitor-interface commands.

- Physical interfaces have monitor-interface enabled by default, so these commands are not explicitly shown in the running configuration unless they differ from the default setting.

- Sub-interfaces, on the other hand, require explicit monitor-interface configuration, which is why these commands were previously visible in the standard show run command output.

- This is a behavioral difference between sub-interface and physical interface default configurations, not a software defect.

Related Content

- https://www.cisco.com/c/en/us/td/docs/security/asa/asa-cli-reference/S/asa-command-ref-S/m_show_is-show_m.html#wp3555445722