09-14-2006 06:50 AM - edited 03-03-2019 02:00 PM
Hi there,
I've got a Cisco 1721 and a BRI interface. The 1721 is connected to the Internet via SDSL on interface Ethernet0. I'd like to use the BRI interface as ISDN backup when the SDSL line is down. Could anyone check my config and tell me if thi the config should work?
interface BRI0
description ISDN-Backup
no ip address
no ip unreachables
ip nat outside
encapsulation ppp
dialer pool-member 1
isdn switch-type basic-net3
isdn point-to-point-setup
no cdp enable
ppp authentication pap chap
ppp multilink
!
interface Ethernet0
description $ETH-WAN$
ip address <ip address> 255.255.255.248
ip load-sharing per-packet
backup delay 1 1
backup interface Dialer0
load-interval 30
half-duplex
!
interface FastEthernet0
description $ETH-LAN$
ip address <ip address> 255.255.255.240
ip directed-broadcast
load-interval 30
speed auto
full-duplex
!
interface Dialer0
ip address negotiated
encapsulation ppp
dialer pool 1
dialer idle-timeout 90
dialer fast-idle 60
dialer string <number>
dialer load-threshold 128 outbound
dialer-group 1
ppp authentication chap pap callin
ppp chap hostname <username>
ppp chap password 7 <password>
ppp pap sent-username <username> password 7 <password>
ppp multilink
Thank you!
Regards, J. Schroeder
09-14-2006 06:54 AM
You will need a floating static route to initiate the BRI connection when the main link goes down:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2010.htm
09-14-2006 07:06 AM
Its good in theory but I think you will find that your ethernet port never goes down.
You have a slim chance when you terminate the dsl connection directly on the router but even then these interfaces tend to stay up.
There are a couple of methods used to solve this nornally. Best is if you can use a routing protocol but unlikely if you are small customer of a isp. One of the new methods to solve this problem is to use policy routing with tracking.
Be aware you also have to have nat configured to use the proper outside address since this is almost always different in configuration such as yours.
09-14-2006 07:28 AM
Okay, thank you! I also thought of tracking an IP address. But could you tell me how to change the config in that way?
09-14-2006 08:03 PM
Check below for the tracking info. & config. sample., try to search "Configuring the Default Route for the Primary Interface Using Static Routing" :
http://www.cisco.com/en/US/products/sw/iosswrel/ps5413/products_feature_guide09186a00801d862d.html
In order to enable the tacking, you have to ensure the ISDN is working and there is interesting packet to trigger the interface.
Hope this helps.
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