Setup ISDN Link as Backup to Primary WAN Link
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Introduction
This document explains how to setup an ISDN link as backup to a primary
WAN link on Cisco routers. A backup link is used when the primary link fails to
provide connectivity. When ISDN is used for backup, an ISDN connection is be
made only if the primary interface goes down for some reason. If the primary
interface and connection go down, the ISDN interface immediately dials out and
tries to establish a connection so that network services are not lost.
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Components
To perform the steps described in this document, you need to have these
items:
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Setup ISDN link as backup to primary WAN link
Follow these steps to configure an ISDN link as backup to a primary WAN
link:
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Setup the router for
Site-to-Site
VPN, if not already done.
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Open a web browser and type
http://router
IP address in the Address
field. The router's IP address is the IP address that you entered in the LAN
Addressing Worksheet (L6A).
Note: For further information on how to launch SDM, refer to
Configure
Your Router with Security Device Manager.
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Click Configure on top of the
screen
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Click Interfaces and Connections from the left
side menu.
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Click ISDN (PPP) radio button, and click
Create a New Connection.
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Click Next.
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Select the switch type that you entered in the Internet Worksheet
(A30) from the drop down menu.
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Check if you have SPIDs, if you enter SPIDs in the Internet
Worksheet (A33, A34).
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Enter the number next to SPID1, if you enter a SPID 1 number
(A33).
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Enter the number next to SPID2, if you enter a SPID 2 number
(A34).
Click Next.
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Enter the ISP ISDN Access Number that you entered in the Internet
Worksheet (A35) in the Remote Phone Number box.
Click Next.
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Follow these steps in ISDN Wizard:
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Choose Static IP Address, and enter the IP
address and subnet mask that you entered in the Internet Worksheet (B46, B41),
if you check Static in field B43 of the Internet Worksheet.
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Choose Easy IP (IP Negotiated) if you check
Dynamic in field B43 of the Internet
Worksheet.
Click Next.
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In ISDN Wizard, follow these steps:
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If you select PPP PAP or PPP CHAP authentication in the Internet
Worksheet (A37), check the appropriate type next to Authentication
Type.
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Enter the username and password in the Username and Password
fields that you entered in the Internet Worksheet (A38,
A39).
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Click the radio-button Configure this connection as
backup.
Click Next.
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Follow these steps:
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Select the primary WAN interface from the drop down
menu.
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Enter the next hop IP address for the primary WAN interface in
the box for Primary next hop IP
address.
Click Next.
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Enter the IP address of the host to which the connectivity is to be
maintained in the Hostname or IP address to be tracked box. This IP address is
tracked by the router for connectivity and in the case primary WAN interface
fails to provide connectivity, ISDN backup is used.
Note: This IP address can be any remote site IP address that is
publically reachable by the primary WAN interface.
Click Next.
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Check the configuration to be delivered to the router in the
Summary screen. Optionally, you can select the box for Test the
connectivity after configuring, to check if the setup is
working.
Click Finish to send this configuration to the
router
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Click Save on top of the screen to save this
configuration to router’s flash.
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Verify the Configuration
Manually bring down the primary WAN link by shutting down the
interface, and follow the steps to
Verify
the ISDN WAN connection.
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Next Step
You have now setup ISDN link as back to primary WAN link on your
router.
Refer to
Router Support
Page to make further changes to your router.
Refer to
Configuration
Overview Page to configure other devices in your network.
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Troubleshoot the Procedure
This section provides information about common problems that you may
encounter. If this information does not solve your problem, contact the
SMB
Technical Assistance Center (SMB TAC) for assistance.
Problem
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Cause(s) and Suggested Solution(s)
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You need more information about the ISDN connection in order to
complete the configuration.
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Contact your Internet Service Provider (ISP) to confirm the
details of your ISDN connection.
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You set up a WAN connection but it does not function
properly.
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See
Troubleshoot
the WAN Connection section.
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You want to set up an ISDN connection in addition to the
primary Internet connection.
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Refer to
Setup an ISDN WAN
Connection.
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Related Information
