VLAN source check verifies to see if BIG-IP can correctly route back a request through the same originating vlan. If BIG-IP determines that it has no way to route a request back through same VLAN, it will drop the packet. Currently, however, in case of TCP, there does exist an alternate route for the originating IP, BIG-IP will send out a RESET packet through the alternate route to indicate that destination is not reachable.
