Hi,
There is no other way than to use VLANs.
The ASA interface will be configured as trunk, while for each VLAN you will configure subinterfaces. Assign one VLAN ID per interface.
The IP of the ASA on each subinterface will be the default gateway for the devices on that subnet.
interface GigabitEthernet0/1
description "Trunk Connectivity with SW"
speed 100
duplex full
no nameif
no security-level
no ip address
!
interface GigabitEthernet0/1.100
vlan 100
nameif VLAN100
security-level 80
ip address xxxxxxx
!
interface GigabitEthernet0/1.200
vlan 200
nameif VLAN200
security-level 70
ip address xxxxxxx
!
interface GigabitEthernet0/1.300
vlan 300
nameif VLAN300
security-level 60
ip address xxxxxxx
An example with VLANs and remote access VPNs:
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a00806ab788.shtml
BTW, ASA does not have Native VLAN support. So if you need VLAN 1 for some reason, you need to create a subinterface for it.
Please rate if this helped.
Regards,
Daniel
