Switch Database Management & Templates of Cisco L3 Switches

Cisco Catalyst switches use TCAM to store information regarding forwarding lookups. There are few templates which are created with different aspects of networking needs. As an example, a L3 switch in a one area will have to perform routing tasks rather L2 switching.

Another switch will need more memory to store L2 information. So to utilize the hardware well to match the networking needs of a particular switch, administrator will have to change the default template the switch is shipped with..

I grabbed a switch from my lab, let's see what is the SDM template of this switch..
Switch#show sdm prefer

It looks like Desktop Default is the SDM template here. You can see 6K is reserved for unicast MAC addresses and 8K is used for IPv4 unicast routes etc..

Let's change this to something else.. How about a routing preferred template?
Switch(config)#sdm prefer routing

After saving and reloading,

As you can see now there are 20K space partitioned for IPv4 unicast routes..

These are pre-built templates. Actually there are 2 versions of each template and they are Desktop version & Aggregator version.. If you enter sdm prefer routing, Aggregator version of routing template will be applied and if you enter sdm prefer routing desktop, Desktop version will be applied.
This is common for every template type..

Following is a chart from Cisco which shows the partitions for desktop and aggregator versions of common 4 templates (access, default, routing, vlan)

SDM Templates in Switch Stacks

All stack members use the same SDM template that is stored on the stack master. When a new switch is added to a stack, as with the switch configuration and VLAN database files, the SDM configuration that is stored on the stack master overrides the template configured on an individual switch..