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Isdn Backup with HSRP

Unanswered Question
Jun 25th, 2003
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customer wants two routers running HSRP for redundancy at site. but where wondering if they could cut costs by setting up on router with leased line and one with isdn.

I see that HSRP can track the serial int on the leased line of the primary router and then hav it take it back once its up (preemt).

But how would the router set up the isdn and take it down?

and also what about routing info?

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lgijssel Thu, 06/26/2003 - 01:23
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Please check out the IOS configuration guide on how to configure Floating Static routes. This is a possible solution. Please beware that the router that connects to the serial line is always the active router. HSRP will then take over in case of a router failure.

Routing info will be redistributed if you configure static routes to be redistributed. This guards against link failures and also takes care that your ISDN connection drops when the serial link comes back. Use a suitable administrative distance.



vcjones Thu, 06/26/2003 - 09:18
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Sure, it is easy as long as you pay attention to the details. You need to run a routing protocol between the router and use either dial on demand or dialer watch to control the ISDN link. You cannot use backup interface.

Deal with HSRP and dial backup independently, because you want your solution to work no matter what the state of either. Then you can tune by having the router with the serial link track the status of the link as part of its HSRP configuration. The issues are discussed in chapter 6 of my book High Availability Networking with Cisco. The final example (Listings 6-23 and 6-24, also available on my web site) uses both HSRP and split dial backup, but also includes capability you probably do not need (survival of LAN segmentation).

Good luck and have fun!

Vincent C Jones



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