Chapter 10 Install and System Administration for FortiOS 5.0 : Advanced concepts : IP addresses for self-originated traffic
  
IP addresses for self-originated traffic
On the FortiGate unit, there are a number of protocols and traffic that is specific to the internal workings of FortiOS. For many of these traffic sources, you can identify a specific port/IP address for this self-originating traffic. The following traffic can be configured to a specific port/IP address:
SNMP
Syslog
alert email
FortiManager connection IP
FortiGuard services
FortiAnalyzer logging
NTP
DNS
Authorization requests such as RADIUS
FSAE
Configuration of these services is performed in the CLI. In each instance, there is a command set source-ip. For example, to set the source IP of NTP to be on the DMZ1 port with an IP of 192.168.4.5, the commands are:
config system ntp
set ntpsyn enable
set syncinterval 5
set source-ip 192.168.4.5
end
To see which services are configured with source-ip settings, use the get command:
get system source-ip status
The output will appear similar to the sample below:
NTP: x.x.x.x
DNS: x.x.x.x
SNMP: x.x.x.x
Central Management: x.x.x.x
FortiGuard Updates (AV/IPS): x.x.x.x
FortiGuard Queries (WebFilter/SpamFilter): x.x.x.x