It seemed strange. I have a Leased line as primary interface and ISDN as backup.
When primary link goes down, ISDN goes up. that's fine.
But when primary link goes up, ISDN is still up. And even if I shut down PRI interface AND dialer interfaces, router show me one open circuit in "show isdn active". I don't get it. How's that? physical interface is down and yet there's an open ISDN circuit?
my IOS version is 12.4(22)T