Interface backup which stays up and without using a routing protocol

[admin_2]

we want to use an ISDN interface a backup for a serial interface on a cisco router. the problem is:

1- the link can be down while the primary interface stays up.

2- We can't use any routing protocol beween the router and the equipment behind the link.

So we can't use floating static route or dialer watch

Is there any other mean to trigger the backup link when the other side equipment becomes unreachable through the primary link?

[#2]

Not really. If this is a FR link,

you could use end-to-end keepalives

to ensure that the primary goes down

in the event of any link failure.

You might also look into snapshot routing

on the serial link, if you are

concerned about the routing overhead

(although a link state protocol would

be better).