Multi WAN IP Setup

Hi Everybody, I am a newbie on RouterOS.

I got a WAN connection with 8 Public IP Address (Actually 5 only)

Public IP 0 - XXX.XXX.XXX.0 - Used by ISP
Public IP 1 - XXX.XXX.XXX.1 - Available for Router OS
Public IP 2 - XXX.XXX.XXX.2 - Available for Router OS
Public IP 3 - XXX.XXX.XXX.3 - Available for Router OS
Public IP 4 - XXX.XXX.XXX.4 - Available for Router OS
Public IP 5 - XXX.XXX.XXX.5 - Available for Router OS
Public IP 6 - XXX.XXX.XXX.6 - Used by Router from ISP (Gateway)
Public IP 7 - XXX.XXX.XXX.7 - Used by ISP

Behind the RouterOS, I have 5 Servers that use 5 different Public IP

Questions

  1. How can I setup WAN Interface? (IP and netmask)

  2. If I setup Source NAT, which Public IP will be used?