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ISDN question


I made a posting some time ago about ISDN related info and for the life of me I cannot find my posting on the forum. So please forgive me for make another posting, but I really need some help with regards to the ISDN issue I am having.

I have a main site, which has a router with a diginet line. This site also has ISDN as a backup.

There are 3 other sites with Diginet lines and ISDN as backups. These sites (all 4 of them) need to use their ISDN lines if the diginet line goes down.

The problem is the routers have never been configured properly for ISDN. So when the diginet line goes down, an administrator must manually unshut the ISDN line. Once the Diginet line is back up the admin must shut the ISDN line again.

As far as I have it, a statement must be put in place on the router something along the lines of

"ip route [Diginet ip address] [subnet mask] [dest ip address]"

"ip route [ISDN ip address] [subnet mask] [dest ip] weight"

So the ISDN line will only be used when the Diginet line is down, cause the weight on the Diginet line is infinite.

If you need any configs, please let me know.

Also can someone please mail me some links about the more technical side & explanations of ISDN. As well as ISDN configurations.

Thank you very much :)


  • Remote Access

Re: ISDN question

Hi ,

can we get of chance of knowing your setup...How these four sites are connected ?

you need to place following commands on serial interface of the router.

int serial 0

ip add x.x.x.x

encapsulation x.x.x.x

backup delay 5 120

backup interface bri x

Note : don't shut the bri interface.

as soon as serial link goes down , isdn will be fired automatically...

you need to add two static routes to destinations on respective routers

First route must have other end serail ip as next-hop.

second route must have other end bri ip as next-hop with AD value.

Plz check the below link.



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