Possible L2 Loop Issue?

[Wonkyu Lee]

Testing Phase Three-way Connection

I need to migrate a traffic path which is going through Fortinet firewall device right now.

Once the migration is done, Data Center network(192.168.1.0, 192.168.9.0) will pass Meraki straight without Fortinet Fortigate firewall.

To test the migration, I am going to connect a cable between Meraki and the Core Switch and pass only a few specific routes (ex 192.168.13.0/24, 10.13.10.0/24). Other subnets will be passed by 192.168.0.0/16.

Once the migration is done, I will remove a cable between Meraki and Foritgate

If I connect Meraki and Core Switch will it create a L2 loop?

[Philip D'Ath]

Are the Foritgate 192.168.2.0 and 192.168.4.0 interaces switched (aka are VLANs) or routed (aka L3 interfaces)?

If they are switched VLANs then yes, you may introduce a loop.

You have a layer 3 switch - I would avoid creating the loop and use the 4507 to control the routing.

[Wonkyu Lee]

Ports on the Fortigate are L3 and Cisco 4507E has L2 & SVI. Since there are L3 ports between MX and Cisco Switch Loop will not happen?

[Philip D'Ath · Accepted solution]

If they are layer 3 then a loop can not happen.