Network Functions Visualization (NFV) builds upon virtualization technology and allows the decoupling of network services from dedicated and complex hardware-based appliances. This decoupling allows network providers to install these functions in commercial off-the-shelf hardware reducing the overall capital and operational expenses. In order to provide complete and high quality services to the end users, a series of these functions may need to be traversed creating a service chain model. In this paper, we study the problem of allocating a dynamic service chain, where a random number of users are associated with each service chain, in a data center network. The allocation consists of the placement of VNFs in appropriate servers and the interconnection between these servers. This interconnection is facilitated by an SDN controller, which proves to be complementary with the NFV paradigm. Towards these aims, we propose two algorithms for the placement of the VNFs, while the SDN controller periodically recalculates the routing paths to adjust to the dynamic traffic conditions.