Basic PIX Configuration

This should be your most basic configuration if you want your PIX to have internet access, assuming there are no other blocking/filtering device that exists between the PIX and the internet:

Topology:
PIX inside: 192.168.102.254 /24
PIX outside: 10.199.248.50 /24
ISP/default gateway: 10.199.248.254 /24



PIX 6.X Configuration:
interface ethernet0 auto
interface ethernet1 auto
nameif ethernet0 outside security0
nameif ethernet1 inside security100
ip address outside 10.199.248.50 255.255.255.0
ip address inside 192.168.102.254 255.255.255.0
global (outside) 1 interface
nat (inside) 1 0 0
route outside 0 0 10.199.248.3 1


PIX 7.X Configuration
interface Ethernet0
 no shutdown
 nameif outside
 ip address 10.199.248.50 255.255.255.0
interface Ethernet1
 no shutdown
 nameif inside
 ip address 192.168.102.254 255.255.255.0
global (outside) 1 interface
nat (inside) 1 0 0
route outside 0 0 10.199.248.3

Notes:
Slight difference when dealing with different PIX OS, but principle is the same. First, configure the interfaces. Next, configure translation (shown here is the simplest NAT). Lastly, configure default route.