one arm setup and two vlans

Typically when people refer to a "one-armed" configuration, it usually means that the virtual-address is on the same vlan and subnet as the application servers, and the application servers are not configured to use the F5 as their default gateway. When the F5 is not the default gateway we have to SNAT client traffic to maintain route symmetry. On the other side of the coin, a "routed", or "dual arm" configuration usually means that application servers are on a different vlan than the virtual-address, and that the F5 has been configured as the default gateway for application servers, which then means we do not need to SNAT client traffic. In either case the F5 is a full proxy and maintains both client side and server side connections regardless of the ingress/egress path.