1. A logical network comprising: a plurality of host machines, each host machine operating a set of virtual machines (VMs) and an instance of a logical routing element (LRE) as a managed physical routing element (MPRE) for routing data packets from the VMs operating in the host machine to network nodes in the logical network; and a plurality of physical routers that do not operate instances of the LRE, wherein multiple MPREs in a subset of the plurality of host machines are selected for responding to address resolution protocol (ARP) messages sent by the physical routers, wherein the multiple MPREs in the subset perform L3 routing on data packets from the plurality of physical routers to the VMs operating in the host machines.