Technical data

Brocade 6910 Ethernet Access Switch Diagnostic Guide 5

53-1002348-02

TCAM partitioning and usage

Ternary Content Addressable Memory (TCAM) is a component of Brocade devices that facilitates

hardware forwarding. As packets flow through the Brocade device from a given source to a given

destination, the management processor records forwarding information about the flow in TCAM

entries. A TCAM entry generally contains next-hop information, such as the outgoing port, the MAC

address of the next-hop router, a VLAN tag, and so on. Once the Brocade device has this

information in TCAM, packets with the same source and destination can be forwarded by hardware,

bypassing the management processor, and speeding up forwarding time.

TCAM stores Layer 2, Layer 3, or Layer 4 information in policy control entries. These entries are

used by various system functions which rely on rule-based searches, including Access Control Lists

(ACLs), IP Source Guard filter rules, Quality of Service (QoS) processes, or traps. For example, when

binding an ACL to a port, each rule in an ACL will use two policy control entries; and when setting an

IP Source Guard filter rule for a port, the system will also use two policy control entries.

TCAM show commands

show access-list tcam-utilization

Syntax: show access-list tcam-utilization

This command shows utilization parameters for TCAM, including the number policy control entries

in use, the number of free policy control entries, and the overall percentage of TCAM in use.

NOTE

The total number of policy control entries is fixed at 640, and cannot be configured.

Console# show access-list tcam-utilization

Total Policy Control Entries : 640

Free Policy Control Entries : 522

Entries Used by System : 118

Entries Used by User : 0

TCAM Utilization : 18.43%

Configuration notes

The Brocade 6910 switch can have up to 512 static and dynamic MAC addresses stored in the

TCAM (using two policy control entries per address). The ability of the TCAM to store large numbers

of addresses depends on the following factors:

• The number of source MAC addresses being learned by the TCAM.

• The number of destination MAC addresses being forwarded by the TCAM.

• The distribution of the MAC address entries across ports. For example, if one port is learning all

the source MAC addresses, the available TCAM will be used up by that port. In addition, a large

number of MAC address entries in the MAC table could increase CPU use.

• The TCAM provides a total of 1000 hardware entries. However, each rule used by the system

for basic functions or configured by the user requires two policy control entries. Some entries

are used by the system for basic functions, L3 lite functions (including static routing and

automatic routing between directly-connected Layer 3 interfaces), web authentication, IP

Source Guard, and any configured ACL rules.