Managing dynamic IP address assignments

Various systems and processes may be used to manage Internet Protocol (IP) addresses that are dynamically assigned. In particular implementations, systems and processes for managing IP addresses that are dynamically assigned may include the ability to determine whether an identifier for a web service has been received from a customer having one or more virtual machines in a service provider network, the web service being accessible by the customer's virtual machines over an external communication network. The systems and processes may also include the ability to determine a number of IP addresses for the web service, identify virtual machines of the customer that are allowed to communicate with the web service, generate one or more IP address lists for the identified virtual machines, and update security tables for the identified virtual machines with the IP address lists at server computers hosting the identified virtual machines.