Default route via Common domain

Hello Roman, keep the parent hierarchy as default. Forwarding virtual server should be in client route domain, so route domain 1 and 2. Try to setup a default route in each route domain (1 and 2) pointing to your firewall ip address in route domain 0 with %0 suffix. then you have to take care of traffic comming as loop back from the firewall to you bigip with a fowrading virtual server. So in rd 0 you should have routes pointing to your servers IPs with gateways in RD suffixed with rd number. This won't tolerate overlapping IPs as you must specifically tell in which rd you'll find which IP.

Make sure VLAN-Keyed Connections is on in general local traffic properties (system menu).

Taking a step back do you really need to use the big-ip as router in such situation ?