The Catalyst 6000 Family consists of the Catalyst 6000 Series and the Catalyst 6500 Series. A six-slot chassis and a nine-slot chassis are available in both the Catalyst 6000 and 6500 series. In addition, the Catalyst 6500 series also supports a chassis with nine vertical slots providing a wide range of configuration and price/performance options. Designed for Network Equipment Building Systems (NEBS) Level 3 compliance, the nine-slot vertical chassis has back-to-front airflow and is ideally suited for service-provider environments. It is also suitable for those enterprise customer environments in which front-to-back airflow is preferred.