Configuring ASA Interfaces

Usually by default internal LAN interface is named "inside", and wan internet interface is named "outside". For every interface You can configure security level. Default security level for inside interface is 100, and for outside interface security level is 0. By default, CISCO do not allow traffic flow from interface with lower to higher security level - which means that by default traffic from inside to outside is allowed, but traffic from "outside" to "inside" is denied. (To enable traffic flow from "outside" to "inside", You have to explicitly allow it with access-list.)

Let's Configure internal interface which we'll name "inside". We can setup ip address and security-level.
Interface is activated with no shutdown command: 

ciscoasa>enable ciscoasa#conf t ciscoasa(config)# ciscoasa(config)# interface GigabitEthernet0/1 ciscoasa(config-if)# nameif inside ciscoasa(config-if)# ip address 192.168.15.1 255.255.255.0 ciscoasa(config-if)# security-level 100 ciscoasa(config-if)# no shutdown

We can name external interface as "outside": 

ciscoasa#conf t ciscoasa(config)# interface GigabitEthernet0/0 ciscoasa(config-if)# nameif outside ciscoasa(config-if)# ip address 211.168.153.12 255.255.255.240 ciscoasa(config-if)# security-level 0 ciscoasa(config-if)# no shutdown

(Notice the port of external interface is "GigabitEthernet0/0 ") 


Put interface in a specific VLAN, example VLAN 2: 

ciscoasa#conf t ciscoasa(config)# interface ethernet0/2 ciscoasa(config-if)# switchport access vlan 2 ciscoasa(config-if)#speed 100 ciscoasa(config-if)#duplex full

(note there's no communication between interfaces in different vlan's unless traffic is routed over L3 device, 
or trunking is configured on some interface so it can accept traffic tagged with different VLAN ID) 

To enable access to You firewall, You have to enable authentication, set up some username and password and enable some access method. Also some basic parameters needs to be set up.