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Configuring an ISDN for the Internet

How can I configure an ISDN line on a Cisco 2600 router for Internet connectivity? What information do I need from my service provider (e.g., switch type and so on)? I would appreciate if you could provide detailed commands to be entered on the BRI interface.

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Configuring ISDN dialup is a very common thing and quite straightforward. You will need to determine a few parameters yourself, but the logic behind it is simple to understand, so I don't think you'll have many problems.

Here's a set of commands used to connect to your ISP via an ISDN dialup:

BRI0 Interface:

interface BRI0/0
 description Public WAN
 bandwidth 64
 ip address negotiated
 encapsulation ppp
 dialer idle-timeout 2600
 dialer string <phonenumber>
 dialer-group 10
 isdn switch-type <switchtype>
 no cdp enable
 ppp authentication chap callin
 ppp chap hostname <username>
 ppp chap password <encrypted password>

Global Parameters:
ip route BRI0/0
access-list 10 permit any 
dialer-list 10 protocol ip permit
What you'll need to keep in mind is that you're going to probably need to configure/change a few of the options above. For example, the "dialer string" number will need to be replaced with your ISP's phone number. The same applies for the PPP CHAP hostname and password, where your account's username and password must be inserted.

The "ISDN switch-type" will have to be configured to the correct type. Your ISP or telephone company should be able to provide you with this information.

In closing, the above configuration is pretty standard, so it should work if all the information provided is correct. If you find yourself unable to complete the connection, I'd advise you to visit Cisco's Web site and perform a search on "ISDN Dialup" and browse through the examples given by Cisco.

This was first published in April 2005

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