A security administrator has configured an IPsec tunnel between two SRX devices. The devices are configured
with OSPF on the st0 interface and an external interface destined to the IPsec endpoint. The adminstrator
notes that the IPsec tunnel and OSPF adjacency keep going up and down. Which action would resolve this
issue?

A.
Create a firewall filter on the st0 interface to permit IP protocol 89.

B.
Configure the IPsec tunnel to accept multicast traffic.

C.
Create a /32 static route to the IPsec endpoint through the external interface.

D.
Increase the OSPF metric of the external interface.

Explanation:
http://packetsneverlie.blogspot.in/2013/03/route-based-ipsec-vpn-with-ospf.html