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New Member

ISDN Backup

We have two ISDN routers with dialup lines for customers. If the isdn line on the first router fails, the second router should bring up the dialup link to the remote site. We are planing to run OSPF and HSRP between the routers on the LAN side.

The question is: how can I backup dialup lines with ISDN.


Re: ISDN Backup


Yes, I think this is possible.

Well, you must confige both routers identically as regards isdn, dialer-list

dialer profile etc., but different on the ethernet and HSRP. Assume that 1 router

is active HSRP router,2 router is standby.When 1 router fails regarding hsrp rules downstream traffic revert to the 2 router and if you confige this traffic like interesting

isdn link come up. But assume that 1 router come back active the downstream traffic revert back to the 1 router but we need that isdn link on 2 router come down so you must undestand behaviour upstream traffic from customer. It must

a) turn to the second isdn link in the case 1 router fails

b) turn back to the 1 router when it come back active

then if this is correct, no more traffic will be on the second isdn link and after some time

it come down.

New Member

Re: ISDN Backup

Yes and no.

Using HSRP and interface tracking (monitored interfaces) if the physical Layer 2 parts of the ISDN failed, the HSPR active router could decrement is priority until the backup took over.

However, if the Layer 2 properties where OK, but you couldn't dial or no reponse from remote end this wouldn't solve your issue(s).

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