Posting the Redundant Redundant piece reminded me of an OSPF-based ISDN dialer backup scenario I designed for a client about three years ago. I haven't seen this is practice since, but it's been a significant help to them, as it gets around the backup-dialer link issues, such as when DCD is up on a frame link, but DTR is down. In that case, the backup dialer will not be invoked, since the link is technically sti Posting the Redundant Redundant piece reminded me of an OSPF-based ISDN dialer backup scenario I designed for a client about three years ago. I haven’t seen this is practice since, but it’s been a significant help to them, as it gets around the backup-dialer link issues, such as when DCD is up on a frame link, but DTR is down. In that case, the backup dialer will not be invoked, since the link is technically still there.Here’s the synopsis sent to Cisco on May 3, 2000, unedited:Remote site 3620 speaks OSPF through frame link to 7206. When it sees OSPF hellos and LSAs arrive, all is well. If OSPF hellos stop, then the router looks for other routing information. There is a static default route in the config with an administrative distance(130) greater than OSPF’s (110). This causes the router to ignore this route when it is receiving OSPF packets. Once the link drops, or the 7206 stops sending OSPF packets, and interesting information hits the remote router, the remote router reads the backup default route: ip route 0.0.0.0 0.0.0.0 dialer1 130 and fires up the dialer through the ISDN line to the AS5300. The AS5300 has been configured to use TACACS authentication for all authentication. It challenges, and checks with the CiscoSecure server for authentication and other information. In the CiscoSecure entry for this remote router, there is an IP address pool specified, which the AS5300 uses to assign an IP to the incoming ISDN call. The local dialer interface on the AS5300 is ip unnumbered to loopback1, and the IP that is assigned to the incoming ISDN call is within the /24 of the loopback. Once the ISDN call has been made, the 3620 speaks OSPF to the AS5300, which then advertises itself as the router that now handles the subnet behind the 3620, and all is well. Once the frame connection comes back up, all routes should be handled through that interface, since the loopback on the 7206 has a higher IP than the AS5300. All routes are then pointed to the S0/0 link, and no traffic flows over the ISDN line, and the line comes down.