Configure Cisco Router 887 FastEthernet port as WAN port

Scenario: Cisco 887 Router (4 LAN Ports) connected to an ISP Fiber Gateway Router HG8244T through one of its LAN port as WAN port.

Cisco887WANPort

You cannot directly set FastEthernet0-3 ports as Layer 3 ports or WAN, neither you can assign an IP address (“no switchport” will not work). In such case, create a VLAN interface with IP address and assign it to FastEthernet port, sample working configuration as below –

ip dhcp pool LANNW
network 10.1.1.0 255.255.255.0
default-router 10.1.1.254
dns-server 212.77.192.59 212.77.192.60
!
interface ATM0
no ip address
shutdown
no atm ilmi-keepalive
cdp enable
!
interface Ethernet0
no ip address
shutdown
!
interface FastEthernet0
no ip address
shutdown
!
interface FastEthernet1
description **CONNECTED TO LANNW**
switchport access vlan 11
no ip address
spanning-tree portfast
!
interface FastEthernet2
no ip address
shutdown
!
interface FastEthernet3
description **CONNECTED TO WAN**
switchport access vlan 100
no ip address
spanning-tree portfast
!
interface Vlan1
no ip address
shutdown
!
interface Vlan11
description **CONNECTED TO LANNW**
ip address 10.1.1.254 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
interface Vlan100
description **CONNECTED TO WAN**
ip address dhcp
ip nat outside
ip virtual-reassembly in
!
ip nat inside source list 101 interface Vlan100 overload
access-list 101 permit ip 10.1.1.0 0.0.0.255 any

Note: “ip routing” is enabled by default in Cisco router.