ISDN Backup - 2501 & 1603 - How do I implement if kilostream goes down

[F1lby]

Hi - I have two routers - Cisco 2501 and 1603
We have a 512K kilostream leased line and a dual channel 128k ISDN line.
Both routers work fine.
Our ISP has given us an ISDN account for backup if the leased line fails.
The 2501 attached to the leased line is set up fine.
If I disconnect the 2501 and use the 1603 I can get it to dial up and work fine offering us the same addressing scheme.
So in the event of leased line failure I can unplug the 2501 and connect the 1603 to continue working as normal.

But how would I implement this as a backup solution to kick in automatically - I dont understand the methods or principles that would be used to automatically detect a line failure and kick in the ISDN backup router - and if the leased line came back, how would the ISDN router go back to being IDLE?

At the moment both routers have the same IP address and are to be plugged / unplugged manually.

I accept they must have different (internal) LAN IP addresses but how does the backup feature work? I guess it must be something to do with modifying routing tables....? maybe ...?

I cant find any documentation covering this subject but I have seen this implemented a number of times by ISPs using Cisco gear... but I've never been able to look at the configs to find out how.

Please help

Kindest Regards

Phil Blythe

 

[marks66]

I have only found one way to have a secondary router backup the leased line of a primary.

Assuming you have a dynamic routing protocol (EG OSPF) then use the dialer watch command on the secondary router.

Config would be something like this.

Primary Router
Ethernet 0/0
ip address 192.168.20.1 255.255.255.0
standby 1 ip 192.168.20.3
standby 1 priority 100
Serial 0/0
ip address 192.168.22.1 255.255.255.252

router ospf 100
network 192.168.0.0 0.0.255.255 area 0

Secondary Router
Ethernet 0/0
ip address 192.168.20.2 255.255.255.0
standby 1 ip 192.168.20.3
standby 1 priority 90
bri 0/0
ip address 192.168.22.6 255.255.255.252
encapsulation ppp
dialer map ip 192.168.22.4 broadcast 0207xxxxxxx
dialer map ip 192.168.22.1 Broadcast 0207xxxxxxx
dialer load-threshold 1 either
dialer watch-group 1
dialer-group 1
isdn switch type basicnet3

dialer watch-list 1 ip 192.168.22.1 255.255.255.252

Ensure all your ethernet workstations have the standby ip address as the default gateway.
The dialer-watch command looks for the ip route of the leased line in the routing table if it is no longer there the ISDN dial starts and the seconday router will advertise the route.

I may not have covered everything here but it should point you in the right direction.

Cheers

Mark

 

[F1lby]

Ah-ha - routing protocols!!!
OK, I'm on the case - this looks good.
Many thanks to you both for your help.
Mark, as you said, you may have not covered everything, but this looks pretty close to what I'm after. The principle looks good!!!