FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.

This article explains how to maintain physical layer 2 ethernet connectivity when running in bypass mode on the FortiGate. This article applies to the following FortiGate devices:-

FortiGate 100D-rev 2
FortiGate 600C
FortiGate 800C

FortiOS v4.0

The below ASCII diagram shows when using bypass ports there has to be 1 (or an odd number) of cross-over ethernet cables in the layer-2 path. Therefore when a pair of ports fail-over in bypass mode, connectivity is maintained :-
NB :-In this example bypass mode is running between 3 FortiGate devices FortiGate 51B, 1000C, and 311B, the cross over cable should be cabled between switch1/port 17 and the FortiGate 1000C/wan1 interface. 
This information does not apply to the standalone FortiBypass appliances.


switch1 : port16 and port17 belong to vlan111          VLAN0111                         active    Fa0/16, Fa0/17


switch2:  port16 and port17 belong to vlan222          VLAN0222                         active    Fa0/16, Fa0/17 

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Technical Tip: FortiGate Bypass interfaces