The reason you can’t delete or add sub-interfaces directly is because once the FTD is managed by FMC, all VLAN and sub-interface changes must be done from FMC, not FXOS. To remove one, go to Devices > Device Management > [Your FTD] > Interfaces, open...

Hey again @MHM Cisco World,Sorry about that, MHM. I had multiple Cisco Community queries open at the same time, and I must have dropped my reply in the wrong spot by mistake. 

Hey @zachartl,You cannot add or delete subinterfaces directly from FXOS once the device is already managed by FMC. FMC becomes the single point of management for all data interfaces and subinterfaces. That is why you are seeing the “no sync” issue in...

Yes, the CLI code I posted is meant to be applied on R1. The idea is that you create an ACL (access list) that permits ICMP (ping) traffic specifically between PC-A and PC-C, and then apply that ACL on the correct interface of R1 in the right directi...