We recently encountered a serious problem with Cisco IOS 12.2(19) and ISDN connections. Our setup was a 7206vxr router with 2 inbound PRIs.
When a remote site would fail over to ISDN backup (from frame relay) and call in to the 7206, the connection would come up correctly. When frame relay service returns, the ISDN connection is supposed to drop after 15 minutes and the ISDN interface on the remote router should return to a standby mode.
After 15 minutes what we saw was the remote ISDN interface indeed going into standby mode, and the frame interface up/up. However looking at the local 7206, we still saw the ISDN connection in a connected state. Thinking that was quite odd, we bounced the PRI interface, which killed all connections (sh isdn serv, etc showed no active lines).
Or so we thought.
When we got a large bill for ISDN usage the next month, we started investigating.
It seems what happens is even though the local and remote routers see no sign of an ISDN connection, it is STILL THERE (confirmed by ISDN provider). So basically we had calls up 24x7 that were not being used.
The reason for this post is to query the user community if anyone else has ever experienced this problem before. Cisco has not yet found this is a bug in their IOS 12.2(19).
This bug started occuring right after we upgraded to 12.2(19), and stopped as soon as we rolled back to our old IOS. This is how we know that it is an IOS bug.
So, any thoughts?