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BACKUP INTERFACE

Unanswered Question
Feb 10th, 2003
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Background: I have 2 routers; 3640 and 3660 connected to the same LAN, each of these routers provides access to remote sites using 1750's via primary Kilostream links with ISDN BRI links as backup. Each 1750 has serial interface providing Kilostream conncetion and BRI interface providing ISDN backup. Each of the 3600 routers has serial E1 interface providing 64K to multiple remote locations and PRI interface providing multiple dialup access for back up. So for example each remote site has a Kilostream link to one 3600 router and the ISDN BRI is connected to the other 3600 router.


Problem: My problem is that on the 3600 routers configuring the serial interface so that when a kilostream channel goes down the router will route the packets via the PRI interface on the alternate router. I have tried setting up the backup interface using the ethernet port on the router and then using static routes to route packets via the LAN. However this only resulted in the router locking me and the rest of the network out.


I am sure that someone somewhere has done this before, and without doubt the solution will incredibly easy and obvious, but I am prepared to humble myself in the interest of learning.


Thanking you in anticipation


Derek Groome

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mark-obrien Mon, 02/10/2003 - 06:56
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Derek,


A backup interface will not work since the "backup" interface is on a different router than the one that has the primary connection. For this to work, you need to be running a routing protocol, and with two main WAN routers, I assume you are. The router having BRI access to a remote location needs to redistribute the route to that remote location into the routing protocol with a higher metric than the router with the Kilostream connection to that remote site has.


Another method would be to use dialer watch. Here is a link to help configure that.


http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fdial_c/fnsprt6/dcdbakdw.htm


Hope this helps.


Mark

derekgroome Mon, 02/10/2003 - 07:12
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Mark

many thanks for taking time out to help. Yes we are using router rip between the 3600 routers, but the remote sites are identified by static routes. Static routes to BRI interfaces are given a metric of 150.


I will give this dialer watch ago and let everyone know how it works out.


regards


Derek Groome

tepatel Mon, 02/10/2003 - 20:26
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  • Cisco Employee,

First of all you need to decide which site will dialout on bri line when the kilo stream went down. In your case, remote sites 1750 should dial to 3600 when primary connection went down.

Now there are multiple ways to configure a backup scheme. Following is the link which will help you to evaluate which scheme is the best one for your network.

http://www.cisco.com/warp/public/123/backup-main.html

Above link has a sample config for various scheme too.

I am not sure which interface is the primary On 1750, you can configure backup interface command to work when the kilostream went down..

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