Ternary Content Addressable Memory (TCAM) is used by Cisco Catalyst switches to store information necessary for hardware processing. Its utilization depends on the features supported by the platform, but the TCAM is generally partitioned into sections designated for unicast routes, multicast routes, VLANs, and entries for routed, VLAN, and QoS ACLs.

All switches ship with default TCAM partitions. For example, the 3560 and 3750 support 6K unicast MAC addresses and 8K unicast IP routes by default. However, an administrator may wish to favor layer two functionality over layer three functionality, or vice versa, depending on the role of the switch. This can be accomplished with Switch Database Management (SDM) templates. (Yes, this is an unfortunate acronym, overlapping with the Security Device Manager application.)

The Catalyst 3560/3750 support several specialized SDM templates in addition to the default. The Routing template supports 11K unicast IP routes and only 3K MAC addresses, whereas the VLAN template supports 12K MAC addresses and 0 IP routes. Notice how the same amount of physical TCAM is repartitioned to better support layer three or layer two features, respectively, while the default template maintains a comfortable balance between the two. The advanced IP services image also provides two IPv4-and-IPv6 subtemplates for dual-stack implementations.

To view the active SDM template and the features it supports:

Switch# show sdm prefer
 The current template is "desktop default" template.
 The selected template optimizes the resources in
 the switch to support this level of features for
 8 routed interfaces and 1024 VLANs. 

  number of unicast mac addresses:                  6K
  number of IPv4 IGMP groups + multicast routes:    1K
  number of IPv4 unicast routes:                    8K
    number of directly-connected IPv4 hosts:        6K
    number of indirect IPv4 routes:                 2K
  number of IPv4 policy based routing aces:         0
  number of IPv4/MAC qos aces:                      512
  number of IPv4/MAC security aces:                 1K

To change the SDM template:

Switch(config)# sdm prefer routing 
Changes to the running SDM preferences have been stored, but cannot take effect 
until the next reload.
Use 'show sdm prefer' to see what SDM preference is currently active.

Note that a reload is required for the change to take effect (the TCAM must be partitioned at boot time).