Cisco Router and WAN ADSL connection with RFC1483 Routing support

If you need to connect to an ADSL with a WAN static ip public address but without the other IP address of the WAN point to point connection this tutorial could be useful. I set up it with an old Telecom Italia Smart 16 connection with 16 IP public address to configure on the LAN interface on my router (a Cisco 2800).

Data from the ISP:

- WAN IP Public Address (usually with subnet mask, it is not in fact a standard point to point connection with 255.255.255.252 subnet mask)

- A range of IP Public Address to configure on the LAN interface (ip public address + subnetmask)

The Cisco 2800 was equipped with:

- ADSL WIC

- n° 2 FastEthernet

I configured only one of the two FastEthernet Interface on the LAN side in the example below.

This is the configuration:

!
!--- The LAN interface configuration of the Cisco 2800 ---!
!
interface Fastethernet0/0
 no shut
 ip address <ip address> <subnet mask> !--- configure here the IP Public address assigned by your ISP ---!
 no ip directed-broadcast
!
!--- WAN interface configuration of the Cisco 2800 ---!
!
interface atm0/1/0
 no shut
 no ip address
 no ip directed-broadcast
 no atm ilmi-keepalive
!
interface atm0/1/0.1 point-to-point
 ip unnumbered Fastethernet0
 pvc <vpi/vci>
  encapsulation aal5snap
 
!--- Telecom Italia PVC values are 8/35 ---!

 !
!
ip classless 
ip route 0.0.0.0 0.0.0.0 <default gateway to isp> !--- the WAN IP public address assigned by your ISP ---!
ip route <default gateway to isp> 255.255.255.255 atm0/1/0.1
!