Setting source-IP on IPSEC VPN interface

[ast1300n]

Several cookbooks and VPN manuals reference the following in their troubleshooting sections:

"On some FortiGate units, such as the FortiGate 94D, you cannot ping over the IPsec tunnel without first setting a source-IP. In this scenario, you must assign an IP address to the virtual IPSEC VPN interface. Anything sourced from the FortiGate going over the VPN will use this IP address."

How do I set the source-IP of my IPSEC VPN interface?  I'd like to be able to ping from our firewalls to each other after creating the tunnel.

[emnoc]

Good , now you and run dynamicRouting ( OSPF ) and  ensure the  OPSF-type is tunnel or pt2pt ;)