1. A method for configuring a logical router that interfaces with an external network, the method comprising: receiving a configuration for a logical network comprising a logical router with a plurality of interfaces that connect to at least one physical router external to the logical network; selecting a separate host machine to host a centralized routing component for each of the interfaces; and selecting a particular one of the host machines for operating a dynamic routing protocol control plane that receives routing protocol data from each of the centralized routing components and updates routing tables of each of the centralized routing components.