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Community Member

ISDN backup line with two routers

Hello everyone!

Here in the diagram attached, there are two routers and two switches. Both routers connect to WAN side but I want only one of them to have ISDN backup line which activates itself only when both WAN sides of two routers being down at the same time.

 Is it even possible? I appreciate your any supports and comments in advance.

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Community Member

You can add a static default

You can add a static default route with AD 2, But in order to make it work you either need a routing protocol running on your WAN link  like BGP or you can use IP SLA to track those WAN links.

Community Member

>>vishalvyas1986 Thanks for



Thanks for your reply!

(1) ISDN is a dial-up session, which according to my understandings charges money based on how long the dialup session is established.
(2) ISDN I/F is always ACTIVE (with I/F status up / up), however it only transfers data when both WAN I/F(which has higher AD values) go down, the static default route will be used. Therefore, ISDN I/F will dial up and start connecting itself.


Is there any other way than changing AD values?



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