What are the differences between the LAN and WAN ports?

[utilityitc]

It seems like a simple question, but what are the functional differences between the two types of ports?  What functions, generally, apply to the different ports?  Why is there a distinction between WAN and LAN?

This is in the context of a Site-to-Site IPSec VPN.  Can I define a VPN with one of the WAN interfaces as the "local" interface?  I have such a VPN defined, but no packets are passing.  The VPN is up, and I have static routing set, but no packets are passing.

[Fullmoon]

you often see WAN, DMZ or LAN labels on Fortigate 200 series and below. This is to help customer having less or no IT admin all. It will speed up the initiative to which interfaces is intended for.

If you dig deeper the functionalities of each role (WAN,LAN,DMZ, Undefined) it will hide/display some functionalities. to make things less complex set the role to undefined. 

[Toshi_Esumi]

In addtion, 2-digit models like 60E has switch hardware/chip controlling LAN ports while WAN, DMZ ports are not (I don't know much about hardware architecture of 3-digit models like 100E). You can't put wan2 for example in a hard-switch (config sys virtual-switch)  as a member. Have to be those LAN ports.

You can of course use one of wan interfaces as internal for VPN without any problems.

[Jaime_Andres]

WAN and LAN tags are more informative and contextual, than functional or operational. Therefore, if you would like, you could perform a Site-to-Site VPN on WAN or LAN ports.

The problem you have with the VPN is another, they may be due to negotiation in phase 1, since it does not lift you. I recommend doing a debug, on the internet there is a lot of information on how to do it; That way you can know why it doesn't work.

[brycemd]

It largely depends on the model you are talking about. From the software perspective it's mostly just what options you are shown in the GUI.

From the hardware perspective there's two main points:

1. Models with switch fabric creating the hardware switch

2. Models with multiple ASICs have certain ports assigned to each ASIC