In need of some help with understanding/resolving a routing challenge we're faced with – here is the scenario/assumptions:
- A web application is running which is hosted in 2 physical locations, Locations A and B
- Traffic either enters through Firewall A in Location A or, Firewall B in Location B depending on the DNS settings
- Each Location has Webservers, say Webserver A in Location A and Webserver B in Location B
- The two locations are interconnected and VLANs run between both locations
- Webserver A and Webserver B are therefore on the same VLAN and in the same subnet
- Webserver A and Webserver B run load balancing such that both are actively processing traffic received through the whichever firewall is active
- Webserver A and B can only have one default gateway, this is set to be Location specific e.g. Webserver A’s default Gateway is Firewall A
The firewalls are Cisco ASA’s, the Web Servers W2003.
The problem I am faced with is that traffic for the web application received on Webserver A may have been received through Firewall B, but with the Default Gateway set to Firewall A, my understanding is that in simple terms the response will never make it back in those circumstances.
If that understanding is correct, what sort of routing techniques could be employed to ensure that the traffic goes back out through the door it came through?