dual WAN, replies leave via incorrect interface

Question

Hello, I am running XG 17.5 and I set up DNAT rule for packets coming to secondary WAN. It works, except case where source address is from WAN1 subnet. Replies to these packets are NATed correctly to WAN2 address, but are routed out via WAN1 interface instead of WAN2. 
 Is it a bug or expected behavior and is there a way to fix it? 
 
 Example: XG WAN1 address is 1.1.1.1, WAN2 address is 2.2.2.2. DNAT rule 2.2.2.2 to 192.168.1.50 
 packet is src 1.1.1.5, dst 2.2.2.2. Reply is src 2.2.2.2 dst 1.1.1.5, but it leaves XG on WAN1 interface, instead of WAN2.

KingChris · Accepted Answer

Hi Martin Hlavaty 
 This is expected behaviour in any linux based system. Direct attached routes take precedence over everything. As such, as your client is within the same WAN IP range as you, the XG will route the traffic out that particular link. 
 The permanent solution to this is to get in contact with your ISP and ask why they have assigned you a /24 public or larger IP range if you do not own these IPs. The temporary workaround to this is to create a static route for the IPs you do not have access to/ownership of and route it out your WAN2 gateway. This will allow the routing to take place. 
 Thanks!