Rate Based Policy Enforcement:
New in NetScaler 9.0 are Rate-Based policies which can be used to control, limit and throttle traffic to various servers. Rate Based Policies use the advanced expression syntax found in the Policy Infrastructure (PI) format of the NetScaler, which is also new for 9.0.
You can monitor the rate of traffic that flows through virtual servers or other User defined entities that are associated with different virtual servers, including URLs, domains, and combinations of URLs and domains.
You can control Citrix NetScaler behavior based on the traffic rate, including throttling the traffic flow if it is too high, caching information based on the traffic rate, and redirecting traffic to a new load balancing virtual server based on the traffic rate. You can apply rate-based monitoring to HTTP and DNS requests. You configure traffic rate limit identifiers to monitor the rate of traffic. These identifiers can include filters, known as rate limit selectors, to restrict monitoring (for example, based on IP addresses or subnets). You specify traffic rate limit identifiers in rules for advanced policies in any feature where these identifiers may be useful, including Rewrite, Responder, DNS, and Integrated Caching.
Rate-based monitors can be based on the number of HTTP or DNS requests, number of packets, transactions or amount of bandwidth being used. This is useful for preventing overloads on a network, preventing security attacks, and diverting traffic once it reaches a certain watermark.