Hi Umair
Just to clarify. Are you assigning the same IP address ie 192.168.20.1/xx on 2 different switches? If yes, you'd need to change that. Use one switch as routing mechanism with the other as only a layer 2 extension. Are you attempting to build a redundant topology? If yes, consider MSTP. Do the switches support VRRP?
Looking at the LACP trunks. What specific switch model are you using?
As for the routing. You'll have routing interface configured on the switch. Ie
VLAN10=192.168.10.1/xx
VLAN20=192.168.20.1/xx
VLAN30=192.168.30.1/xx
and so on
You can then create a final VLAN=Internet and configure a port as access (untagged) that will connect to your firewall. Let's say the firewall's IP address is 10.10.10.254/24. Configure a routing interface on the switch as 10.10.10.1/24 as the default next-hop needs to be in the same subnet.
You'll next configure a default route as follows:
0.0.0.0/0 10.10.10.254 to match all outbound traffic.
On the firewall you'd need reverse route to each of the internal subnets. The next hop from the firewall's perspective would the routing interface in the internet VLAN.
192.168.10.0/xx 10.10.10.1
192.168.20.0/xx 10.10.10.1
192.168.30.0/xx 10.10.10.1
And so on.
Hope this helps. Please send me answer to questions above and I'll provide more detailed configuration.
Regards,
Francois