A network administrator is deploying a new Cisco Secure Firewall Threat Defense (FTD) firewall After...

If inside clients have intermittent connectivity issues and the Cisco Secure FTD is responding to all ARP requests on the inside network, it indicates that there may be an incorrect proxy ARP configuration in the NAT policy. Proxy ARP can cause the FTD to respond to ARP requests on behalf of other devices, leading to connectivity issues.

Steps to resolve:

Review the NAT policy on the FTD to identify any incorrect proxy ARP configurations.

Disable the proxy ARP setting for the relevant NAT rules that are causing the issue.

This ensures that the FTD only responds to ARP requests as needed, preventing it from interfering with normal ARP traffic on the inside network.