2 X 2500s back-to-back. RP is OSPF, IOS is late 12.1. Primary Link is Serial0s. Secondary Link is BRI0s. Backup is via Dialer Watch. The Dialer-list is configured to deny OSPF and permit everything else. When the primary goes down and the watched route disappears the BRI0 link activates and the new routes are installed OK. My question - when the idle-timeout expires the BRI0 disconnects and immediately reconnects (the routing table does not change) is this the correct behaviour? I expected the Idle timeout would reset without the BRI0 dis/re-connecting. If the Dialer-list is changed to allow OSPF,hellos bring the line up regardless of the state of the Primary. Thanks in anticipation.
I already used that tech note in my investigations.
It shows debug output for the primary going down and coming back up. That all works fine.
It doesn't show any debug output for the idle-timeout expiry period. i.e what happens when the primary stays down and the idle-timeout expires and resets. Should the BRI0 stay up, or dis and then re-connect ?
It is doing the correct behaviour. As long as the dialer-watch route is down, it will keep redialing. It makes sense if you think about it. ISDN is down to start with. The route drops, so the ISDN kicks in. The idle timer starts and finally ends due to no interesting traffic. ISDN drops and is back to the stage when the route first dropped (ie ISDN down). However the route is still down as per the dialer-watch. So the ISDN has to kick in again (from it's point of view it doesn't know/care if the route just dropped or never came up) to repeat the cycle. Interesting traffic across the link or higher idle times would prevent this.
Yep, the behaviour is perfectly alright. To add up to Steve's point, you can additionally use, ip ospf demand-circuit, which would prevent the hellos from initiating the link. when demand circuit is freshly configured, the isdn link would come up once, routes are exchanged, and link will go down, after idle timer expires. THis would help you to remove the line of denying Ospf packets in the dialer-list ACL.
A simple trick you can use to keep the link up while it is idle (while still dropping it with a reasonable timeout when it is no longer needed) is to configure BGP or some other protocol with a periodic keepalive and set up the routing so the keepalives use the primary link when up and the backup link when not.
I used to use this trick all the time back in the days before dialer watch. There is an extended discussion in Chapter 5 of my book, the example configurations are on my web site.
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