DrayTek LAN-to-LAN VPN Configuration

Hi Experts,

I need to setup a VPN between to sites. on both sites we are using Draytek 2860 routers. I wanted to configure this as standard LAN-to-LAN.

the reason for the VPN is to connect our Avaya IP Phone system to a branch site down the road in order for 4/5 IP Phones to operate. they have only requested that it is a 'normal LAN-LAN'.

I have 3 questions:

1 - Main Mode or Aggressive Mode? - I have read the descriptions and I understand that it depends if you use a fixed IP or not. But how would I know if it was a fixed IP or not?
2 - Call direction, 'Both' 'Dial-Out' or 'Dial In'. I assumed it was 'Both'
3 - the configuration for the Dial-Out settings would surely be the same for the Dial-In settings? both need to be the other sites external IP, correct?

hope someone can help me with this.

peggiegreg