hi guys plz help me in this,

i have 3 routers connected to each other like this

O------------O----------O

R1 ISP R2

i m using a tunnel over ipsec to allow routing via ospf between R1 and R2 everything goes fine, but when the tunnel goes down so does the adjancy, but when the tunnel is up ospf is not making adjancy again automatically !!!! how can i do it ? i want both routers to detect that the tunnel is up and start sending hellos again so that the adjancey is rebuilt but i dont know how, plz tell me

thanks in advance