questa e' un configurazuione base che funziona in un'adsl come la tua...

hostname Router1
!
ip subnet-zero
!
no ip dhcp-client network-discovery
!
!
!
interface Ethernet0
ip address 192.168.2.254 255.255.255.0
ip nat inside
!
interface ATM0
no ip address
ip nat outside
no atm ilmi-keepalive
dsl operating-mode auto
!
interface ATM0.35 point-to-point
ip address xxx.yyy.zzz.hhh 255.255.255.252 *QUESTO INDIRIZZO E'
PUBBLICO
ip nat outside
pvc 1/33
protocol ip XXX.YYY.ZZZ.GGG broadcast *QUESTO INDIRIZZO E' QUELLO DEL
POP
!
!
ip classless
ip route 0.0.0.0 0.0.0.0 ATM0.35
no ip http server
!
ip nat inside source list 101 interface ATM0.35 overload
ip nat inside source static tcp 192.168.2.254 23 xxx.yyy.zzz.hhh 23
extendable
access-list 101 permit ip any any
!
line con 0
transport input none
stopbits 1
line vty 0 4
password CISCO
login
!
scheduler max-task-time 5000
end