Performance Impact And Salability Considerations; Performance Impact; Scalability Considerations; Cam Device Block Size And Cam Entry Allocation - Juniper POLICY MANAGEMENT - CONFIGURATION GUIDE V11.1.X Configuration Manual

Performance Impact and Salability Considerations

The following sections describe how the memory usage and performance of the line
modules on which the variable-sized CAM entries are supported is affected, and also
of the maximum number of policies that can be supported with variable-sized CAM
entries.

Performance Impact

Some performance impact might occur due to the variable size of the CAM entries.
This performance impact is caused by CAM addressing, which works on 72 bits.
576-bit classification requests now require up to 8 lookups to the CAM hardware (8
* 72 = 576). The CAM device has a search rate of up to 83 million per second for
144 bit entries.

Scalability Considerations

One CAM entry is required per classifier for each unique policy on each line module.
Regardless of the classifier definition for an IPv4 policy, each IPv4 classifier consumes
144 bits (one 144-bit CAM entry). However, default classifiers do not consume CAM
entries.
As described in "Variable-Sized CAM Classification for IPv6 Policies Examples" on
page 171, an IPv6 CAM entry size is 144 bits, 288 bits, or 576 bits, depending on the
sum of the classification fields in the policy definition. However, all IPv6 classifiers
consume the same CAM entry size in a policy.
The following factors are used to determine the CAM resources available for policies
when variable-sized CAM entries are present:

CAM Device Block Size and CAM Entry Allocation

Using GE-2 line modules, for example, we can demonstrate how the number of CAM
entries it supports is divided into different blocks to store policies. GE-2 line modules
contain 64,000 144-bit CAM entries. Each entry is divided into eight 8000 144-bit
blocks. Each block can hold equal-sized CAM entries only 144-bit, 288-bit, and
576-bit CAM entries. If no more IPv6 policies are created and when the remaining
seven blocks are used, the 576-bit CAM block is not available to store IPv4 policies
that require 144-bit CAM entries only.
A default classifier within a policy also consumes the same sized CAM entry as the
size computed for the policy. In lower numbered releases, a single 144-bit entry was
reserved for default classifiers. In this release, the number of 144-bit entries reserved
for default classifiers depends on the number of blocks assigned for such CAM entries
and whether the attached policy contains 288-bit or 576-bit entries. For example, if
the first block is used by the 576-bit CAM entry, four 144-bit entries are reserved for
the default classifier.
CAM Device Block Size and CAM Entry Allocation on page 175
Number of CAM Entries Per Allocation and Free Entries on page 176
Performance Impact and Salability Considerations
Chapter 8: Policy Resources
175