Modeling and Evaluation of Address Resolution Scalability in VPLS

More and more services are provided by large data centers with a potentially very large number of either physical or virtual hosts. As the number of hosted services and service consumers increases, also the number of hosts inside a data center needs to increase to cope with the increasing end-user demand. The internal network in a data center is often based on Ethernet and upcoming mechanisms like load balancing or redundancy between data centers require a transparent connection of these Ethernet networks over a wide area network. Due to their large number of hosts, these inter-connected data center networks face scalability issues on different protocol layers. One such issue, which is currently discussed within the IETF, is the scalability of the link-layer address resolution protocol (ARP). This paper studies the control traffic caused by address resolution for inter-connected data centers. We first develop an analytical model for the ARP traffic between data center locations that takes into account the number of hosts and connected sites. This model can then be used to quantify the ARP traffic for a data center interconnect solution. As an example, we apply our model to Virtual Private LAN Services (VPLS). In addition, we study how an ARP proxy can improve the overall scalability, and we show that a proxy significantly reduces the ARP traffic at VPLS switches.