Cisco 1841 with ADSL card

This is Cisco 1841 Integrated Services Router connected to ADSL PSTN BT line with O2 Broadband configuration.

o2 broadband configuration

This paragraph is also here Cisco 1941 with EHWIC-VA-DSL-M o2 is one of this UK odd ISPs who is using RFC 1483 Bridge when providing ADSL2+ Internet access. Below are details provided by O2 and config build on this information.

ISP name: O2 Home Broadband  
Encapsulation: RFC 1483 Bridged
Multiplexing method: LLC-Based 
VPI: 0  
VCI: 101  
Username: leave blank  
Password: leave blank  
Domain name: leave blank  
IP address type: this depends on whether you chose our static IP address option or not:
    If you didn't choose our static IP address option, set this to dynamic IP
    If you did choose our static IP address, enter the IP address printed in your welcome letter  
DNS servers: choose to get these dynamically from the Internet provider  
NAT: enable  
Primary DNS server: 87.194.255.155  
Secondary DNS server: Leave blank 

If you have a static IP address, you should enter the following DNS server address:
Primary DNS server: 87.194.255.154
My o2 box MAC address: 00-24-17-80-42-d0

A BVI (Bridged Virtual Interface)

is a virtual interface that acts like a normal routed interface. A BVI does not support bridging but actually represents the corresponding bridge group to routed interfaces. The interface number is the link between the BVI and the bridge group. Think of the BVI as the default gateway to all the bridge interfaces, all local traffic is bridged between the bridge interfaces, but the traffic that is not local to the bridge group is routed via the BVI interface. Read more on Cisco Community

Integrated Routing and Bridging

bridge irb command enables Integrated Routing and Bridging, then sub-interface atm0/1/0.1 and gi0/0 belong to the same Bridge Group 1 having both bridge-group 1 in their interface configurations. BVI1 (bridge virtual interface) is configured to represents both atm0/1/0.1 and gi0/0 interfaces when ip protocol is routed. Two lines at the bottom bridge 1 protocol ieee and bridge 1 route ip define the Bridge Group 1 is using IEEE bridge protocol and routes IP protocol.

Below config is working with O2 as of 8th Oct 2013, public ip address is provided by ISP dhcp server. Please see sub-interface atm0/1/0.1 command ip address dhcp therefore static ip route something like ip route 0.0.0.0 0.0.0.0 O2_gateway_ip is excluded. Please think about both commands when configuring static IP address given by O2.

Configuration step-by-step

Configure ATM interface

interface ATM0/0/0
 no ip address
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 atm restart timer 300
 no atm ilmi-keepalive
 dsl operating-mode auto
 no shutdown
!
interface ATM0/0/0.1 point-to-point
 description Link to O2 Broadband
 ip address dhcp
 ip nat outside
 ip virtual-reassembly in
 atm route-bridged ip
 pvc 0/101
  oam-pvc manage
  encapsulation aal5snap

Enable NAT port translation on nat-inside fa0/0 local LAN gateway interface and atm0/0/0.1 nat-outside

interface FastEthernet0/0
 ip nat enable
interface ATM0/0/0.1 point-to-point 
 ip nat enable

Catch traffic using access-list

access-list 1 remark Local network PAT-to-internet
access-list 1 permit 10.0.0.0 0.0.0.255

Enable NAT overload

ip nat source list 1 interface ATM0/0/0.1 overload