Chapter 2 Advanced Routing for FortiOS 5.0 : Border Gateway Protocol (BGP) : Dual-homed BGP example : Configuring other networking devices
  
Configuring other networking devices
There are two other networking devices that need to be configured: both ISPs’ BGP routers.
The ISPs’ routers must add the FortiGate unit as a neighbor so route updates can be sent in both directions. Note that ISP1 is not directly connected to ISP2 that we are aware of.
Inform both of your ISPs of your FortiGate unit’s BGP information. Once they have configured their router, you can test your BGP connection to the Internet.
They will require your FortiGate unit’s:
IP address of the connected interface
Router ID
your Company’s AS number