BGP or VLANs for using a Fortinet as a Gateway

Question

Hi all,

I've taken over the network for a company that has a bunch of Fortigate 60E boxes that are using BGP to route between them and it's working fine however we have one at a location that is connected via it's WAN connection to a LAN port on a 60E at another site and then it uses THAT Fortinet as it's gateway. On the 60E without it's own internet connection there are VLAN's on the LAN interface but then there are also the same VLANS on the "wan" interface pointing to the other 60E but then they're not on the 60E that is the gateway (i.e the one that DOES have it's own Internet connection). I want to remove this and just add BGP but one of the techs says that this was done by their previous network admin and he said it had to be done that way due to a Fortinet being used as a gateway by another Fortinet ?

Can anyone confirm this or am i safe to strip this out and just put BGP back in it ?

Thanks in advanced.

Toshi_Esumi · Answer

Technically what you described for the network arrangement on the 60E that has the VLAN is not possible. Because the same VLAN can't be on both LAN and WAN ports without having a soft-switch binding them together. You must be missing something or misreading what's configured on it.

The VLAN/L2 network works underneath the BGP/L3 network. But with FortiGates, an L3 interface has close binding with the L2/VLAN interface. Read the VLAN/interface and switch configuration with all subnets carefully and create a diagram to understand the previous person's intention how the current setup has been working.

Generally if multiple FortiGates on one physical sites connected each others. it either for performance or network segmentation. The diagram would give you more clear understanding.

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