Multilayer switches can be used for a number of different tasks. We can use them for switching, routing or a combination of both. Cisco switches use the TCAM (Ternary Content Addressable Memory) to store layer 2 and 3 information for fast lookups. If you have no idea what TCAM is about, you might want to read my lesson about CEF before you continue.
SDM (Switching Database Manager) is used on Cisco Catalyst switches to manage the memory usage of the TCAM. For example, a switch that is only used for switching won’t require any memory to store IPv4 routing information. On the other hand, a switch that is only used as a router won’t need much memory to store MAC addresses.
SDM offers a number of templates that we can use on our switch, here’s an example of a Cisco Catalyst 3560 switch:
SW1#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: 0.5K
number of IPv4/MAC security aces: 1K
Above you can see that the current template is “desktop default” and you can see how much memory it reserves for the different items. Here’s an example of the other templates:
SW1#show sdm prefer ?
access Access bias
default Default bias
dual-ipv4-and-ipv6 Support both IPv4 and IPv6
ipe IPe bias
routing Unicast bias
vlan VLAN bias
| Output modifiers
Here are the SDM templates for this switch. We can change the template with the sdm prefer command: