Ping from subinterface to physical interface ip

Hi experts; I am newbie in networking and need some help please 

I created 3 VLANs on my Cisco Switch, and configured appropriate Ports (3 untagged and 1x trunk port to the FTG)

I configured 3 VLANs from the "Internal" physical interface (10.20.100.1/24), where the Switch is connected to.

VLAN 10 (Management), Subnet 10.20.10.1/24 

VLAN 20 (WLAN), Subnet 10.20.20.1/24 

VLAN 30 (Data), Subnet 10.20.30.1/24

I created Firewall policies to allow the VLANs to communicate between each other. It's working fine.

My Problem:

While I am in VLAN 10 (NIC  configured with two IP Addresse: 10.20.10.15/24 and 10.20.100.15/24): 

1. If I untag VLAN 100 in trunk port,  I can ping the IP of the physical port 10.20.100.1 (which is the firewall management IP address) but not the VLAN 10 IP Address

2. If I Tag VLAN 100 in trunk port I can no longer ping vlan 100.

My question:

How can I ping both physical interface IP and sub interface IP while I am in subinterface?

Thank you in advance for your assistance