I have completed this lab on pemu windows version, the topology is as follow:

1. Configure address and NAT.

pixfirewall(config)# interface e0
pixfirewall(config-if)# ip address 218.1.1.1 255.255.255.0
pixfirewall(config-if)# no shutdown
pixfirewall(config-if)# nameif outside
INFO: Security level for “outside” set to 0 by default.
pixfirewall(config-if)# interface e1
pixfirewall(config-if)# ip address 172.16.254.1 255.255.255.0
pixfirewall(config-if)# no shutdown
pixfirewall(config-if)# nameif inside
INFO: Security level for “inside” set to 100 by default.
pixfirewall(config-if)# exit
pixfirewall(config)# nat (inside) 1 172.16.254.0 255.255.255.0
pixfirewall(config)# global (outside) 1 interface

2. Configure AAA authentication.

pixfirewall(config)# aaa-server test protocol radius
pixfirewall(config)# aaa-server test (inside) host 172.16.254.10 cisco
!
pixfirewall(config)# access-list access-internet extended permit ip any any
!
pixfirewall(config)# aaa authentication match access-internet inside test
!
pixfirewall(config)# access-list access-internet extended permit ip any any
pixfirewall(config)# aaa authentication match access-internet inside test