How to Configure PPPOA DSL on a Cisco IOS Router

Configuring DSL on a Cisco IOS router can sometimes be quite challenging for those who are unfamiliar with Cisco-class routers or who haven't had to manage DSL settings because their ISP provided the DSL modem. In this short tutorial, I'll guide you through the necessary steps to establish a working DSL connection.

I'll focus solely on DSL configuration, so we won't cover topics like NAT/PAT or DHCP configurations.

To get a functional DSL connection, we need to first address several key elements, such as:

• Configuring a dialer interface

• Applying PPP (Point-to-Point Protocol) configuration and L3 settings to the dialer interface

• Setting up the ATM (Asynchronous Transfer Mode) configuration on the ATM interface

• Linking the ATM interface to the dialer interface

• Configuring a default route to direct traffic through the dialer interface

Let's start with the first step: configuring a dialer interface with all the necessary PPP settings.

Router(config)#interface dialer 1
Router(config-if)#encapsulation ppp
Router(config-if)#ip address negotiated
Router(config-if)#dialer pool 1

Router(config-if)#ppp authentication chap calling
Router(config-if)#ppp chap hostname MYUSERNAME
Router(config-if)#ppp chap password SECRET

First, we need to configure the dialer interface to use PPP encapsulation and to request an IP address from the ISP via PPP. The dialer pool command indicates that when the dialer interface attempts to establish a connection, it should utilize a member interface from the specified dialer pool. We'll configure the ATM interface as a member of this pool shortly.

We also set up the dialer interface to use CHAP (Challenge Authentication Handshake Protocol) authentication, specifying MYUSERNAME as the username and MYSECRET as the password. While not all ISPs require authentication, this configuration is applicable if it is needed.

Now, let's move on to configuring the ATM interface:

Router(config)#interface ATM 1/0               
Router(config-if)#pvc 0/42                        
Router(config-if-atm-vc)#encapsulation aal5mux ppp dialer
Router(config-if-atm-vc)#dialer pool-member 1

First, we need to configure the PVC (Permanent Virtual Circuit) on the ATM interface. In this example, I'll set the VPI/VCI values to 0/42. Keep in mind that these values may differ based on your ISP, so it is best to contact them to obtain the correct settings. If you still have an active DSL connection through your current modem, you can usually find these values in the modem's statistics or metrics area within the administrative interface.

Next, we will configure the encapsulation to aal5mux and specify that we want to use the PPP dialer. The command dialer pool-member 1 will link our ATM interface to the dialer interface.

Last, but not least, we'll create a default route pointing out of the dialer interface:

Router(config)#ip route 0.0.0.0 0.0.0.0 dialer 1

This configuration will route all packets with an unknown destination out of the dialer interface towards the ISP. If you encounter any issues, Cisco provides an excellent troubleshooting checklist on their website that can help you diagnose any additional problems encountered.

Once your DSL connection is up and running, be sure to configure the NAT/PAT protocols for your internal hosts to use; otherwise, they won't be able to access the internet. Remember that when setting up NAT/PAT, you should designate the dialer interface as the NAT outside interface.

If you have any questions, please leave below. I hope you found this tutorial useful!

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Thanks for reading: How to Configure PPPOA DSL on a Cisco IOS Router, Sorry, my English is bad:)