Configure ISDN as indicated.
Advertise in OSPF Area0.
Configure OSPF demand-circuit to bring up the ISDN if there is a change in the database. See Example 3-18 for ISDN working when switch1 port 2 was disabled for R1 in VLAN-12.
Example 3-18 also shows that OSPF converges when ISDN comes up and all routes are learned via BRI.
Configure PPP multilink and load threshold. See Example 3-18, where both B channels are up.
r1#show dialer BRI0/0 - dialer type = ISDN Dial String Successes Failures Last DNIS Last status 99047132 7 0 00:00:14 successful 0 incoming call(s) have been screened. 0 incoming call(s) rejected for callback. ...