Fortigate Gateway NAT Problem

Forum|Forum|9 months ago
October 31, 2025
8 replies
966 views

I have a Fortigate firewall. The management IP block is 172.16.1.1/24.

Fortianalyzer(172.16.1.10) is in this range.. I have an SMTP server, and only the IP address 192.168.1.100 is allowed to access it. I can access the SMTP server by NAT my 172.16.1.10 server. However, I cannot access the SMTP server using the Fortigate management interface (172.16.1.1). NAT is not working.

FortiGate

Best answer by funkylicious

try adding this ip either as a secondary on a existing interface in root vdom or create a loopback and assign it that IP and see if that works.

funkylicious

SuperUser

hi,

i think you can set the source ip from cli for smtp, https://community.fortinet.com/t5/FortiGate/Technical-Tip-How-to-configure-alert-email-settings/ta-p/194102#:~:text=logs%20enable%0Aend-,From%20the%20CLI%3A,-To%20configure%20the

"jack of all trades, master of none"

rcpdkcAuthor

Explorer II

I entered the management interface IP address as the source IP. I also added the NAT rule, but it still isn't NAT.

funkylicious

SuperUser

local originating traffic from the FGT isnt subject to NAT, only for traffic passing through.

just try to enter as source the IP that is allowed on the remote SMTP, see if it works.

"jack of all trades, master of none"

ElwinBERRAR

Explorer III

The error means the IP you’re trying to use isn’t assigned to any interface in the root VDOM. You’ll need to use an IP that actually belongs to an interface in that VDOM, or create a loopback and assign it there first.

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