FPGA Hardware Classifiers

Classification is the process of taking a single data stream in and sorting it into multiple output substreams. The classifier engine on an E Series router is a combination of PowerPC processors, working with an FPGA for a hardware assist.

In the Differentiated Services (DiffServ) architecture, two basic types of classifiers exist. The first classifier type is a multifield (MF) classifier. The MF classifier can examine multiple fields in the IP datagram header to determine the service class to which a packet belongs.

FPGA hardware classifiers are supported on all line modules except the OC48/STM16, GE-2, and GE-HDE line modules. Policy Resources Overview lists the FPGA classifiers and software classifiers supported for each interface type.

An E Series router supports two versions of policies that are based on FPGA hardware classifiers. One version has a maximum of 16 classifier entries per policy, and the second version has 17 to 32 classifier entries per policy. The line module supports 16,255 policies when all policies have 16 hardware classifier entries or fewer, and supports 8127 policies when all policies have 17 to 32 hardware classifier entries.

You can configure a combination of the two versions of FPGA hardware classifier-based policies—you can have some that contain 16 or fewer classifier entries and others with more than 16 entries. In this case, between 8127 and 16,255 policies are supported, depending on the actual configuration.

You can also configure hardware classifier-based policies that have more than 32 classifier entries. The router groups the classifiers into blocks of 32. For example, if you configure a policy with 100 classifier entries, the router groups these as 3 policies that have 32 classifier entries and 1 policy with 4 classifier entries. The group with 4 classifier entries actually consumes 16 classifier resources, which is the minimum number consumed for a group in a mixed-mode hardware classifier configuration.

Unlike policies that are based on software classifiers, policies that are based on FPGA hardware classifiers consume resources at a rate of one resource per policy, regardless of the number of different hardware classifier categories in the policy. For example, if a classifier list has three hardware classifiers, such as destination address, source address, and protocol, the policy referencing that classifier list consumes only a single hardware classifier resource.

The same is true when multiple policy rules reference the classifier list. For example, if four policy rules reference the same classifier list (which contains three hardware classifiers), then still only one classifier entry is consumed.