Cam Device Block Size And Cam Entry Allocation; Number Of Cam Entries Per Allocation And Free Entries - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - POLICY MANAGEMENT CONFIGURATION GUIDE 2010-10-04 Configuration Manual

Copyright © 2010, Juniper Networks, Inc.
As described in "Variable-Sized CAM Classification for IPv6 Policies Examples" on page 162,
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 on page 167
Number of CAM Entries Per Allocation and Free Entries on page 167

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.

Number of CAM Entries Per Allocation and Free Entries

The total number of CAM blocks is divided into two equal partitions. The first or lower
half of the CAM blocks is reserved for 144-bit CAM entries, and the second or higher half
of CAM blocks is reserved for the combination of 288-bit and 576-bit CAM entries, when
an IPv6 policy that contains 288-bit or 576-bit CAM entries is attached to an interface.
If IPv6 policies do not contain 288-bit or 576-bit CAM entries, all the blocks are used for
144-bit entries.
Assume that, on a GE-2 line module, out of the total of eight blocks, four blocks are
completely used for 144-bit CAM entries and the remaining four blocks are allocated in
common for 144-bit, 288-bit, and 576-bit entries. Each of the blocks reserved exclusively
for 144-bit entries can contain 8000 entries, while each of the blocks reserved for the
combination of the variable-sized entries can either contain 2000 576-bit entries or 4000
288-bit entries. The block that is common to the variable-sized entries is available for
144-bit entries only if an IPv6 policy does not contain 288-bit or 576-bit entries. Otherwise,
when the first IPv6 policy that contains 288-bit or 576-bit entries is attached to an
interface and if previously configured policies consumes more than 4 blocks, the IPv6
policy attachment fails.
The block that is common to the variable-sized entries is not available for 144-bit CAM
entries when you configure any 288-bit or 576-bit entries, even though you remove them
Chapter 8: Policy Resources
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