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Community Member

Multiple ISDN dialin routers and routing issues


I currently have a single router with 4 isdn bri interfaces. This is used to dial out and accept connections from 5 different external clients, we have no control over the remote routers and we cannot run any routing protocols over the dialup links.

I need to add a second router to provide redundancy. This router will have an isdn pri interface. Remote routers will be updated with the addition of a dialer string with the new number.

The ethernet interfaces for both routers will be located on the same network and subnet. I can only run rip on this network.

I have a few concerns and problems:

how should I approach the issue of clients dialing into both routers and guaranting that the return packets will always be routed via the active link?

ie, if the router2 with pri is the preferred route but the remote network dials the router1 with bri how can I be sure that the return packets will use the router1-bri interface.

any ideas/reccomendations?


Community Member

Re: Multiple ISDN dialin routers and routing issues


if I well undertood, you desire to use only one link as an active one and the second only as a backup. In this case you could use HSRP on the routers and "track" (standby "xy" track interface) the bri or dialer interfaces -> in case of down state of this interface on the active HSRP, the standby router will switch to active.

If not, please provide more details.

Hope this helps


Community Member

Re: Multiple ISDN dialin routers and routing issues

the hsrp and tracking will work ok but will cater for calls which orinate from my central office towards the remote sites, ie all outgoing calls will be routed via the primary router1 and in case of failure will then failover to the secondary router2.

My issue is how to guarantee that if a remote site dials into router2 that the return route will pass via router2 even if router1 is the primary, in this scenario packets will enter via router2 but will return via router1.

I can't see any way around this for the moment....

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