Enforcing egress address and interface linkage

[kangnguyen]

Hi, We have two WAN links connected to their respective ISP's via the DC operator via link networks. Each interface leads to BGP routers announcing different ranges. We're NAT'ing traffic from the inside via specific egress addresses (partner whitelists), but would like for failover to the secondary interface to function properly in case the preferred one goes down. The problem I'm seeing is that traffic is going out through WAN2 with source-addresses set to addresses that only work with WAN1 and vice versa. How do I teach our fortigates that not all external ip addresses can be used as source address when going through any old cable connected to the SD-WAN interfaces? Thanks for help. Kang Nguyen

[emnoc]

You choices are to doing all or any of the following 1> use SDWAN 2> enable asymmetrical routing 3> deploy a edge router upstream to handle the BGP 4> and review your route table and preferences

I'm sure your route table probably has duplicate route and one being preference. I would 1st start by looking at your destinations routes and maybe applying a route-map that set ISP1 pref to  a value higher than routes learned by ISP2, but in reality that only controls egress leaving your AS and if the ISP1/ISP2 are carrying the same network, return traffic could come back between either of the two.

Show us your route-table and the  fwpolicy .

Ken Felix