Cisco switches use the Ternary Content Addressable Memory (TCAM) to store Layer 2 and 3 information for faster lookups, utilizing the Switching Database Manager (SDM) to manage TCAM memory utilization. A Cisco SDM Template pertains to the configuration templates that enhance the usage of a Cisco switch’s physical resources.
The switch SDM templates can be used to configure system resources based on how the switch is operated in the network to support particular functions or to balance system resource usage.
SDM Template Number of Resources
The approximate number of resources available for each template is shown below. The number may differ depending on the switch platform or software version used. These are standard values for Layer 2 and IPv4 features.
| Resources | Advanced | VLAN |
| Number of VLANs | 4094 | 4094 |
| Unicast MAC addresses | 32000 | 32000 |
| Overflow unicast MAC addresses | 512 | 512 |
| IGMP groups and multicast routes | 4000 | 4000 |
| Overflow IGMP groups and multicast routes | 512 | 512 |
| Directly connected routes | 16000 | 16000 |
| Indirectly connected IP hosts | 7000 | 7000 |
| Policy-based routing access control entries (ACEs) | 1024 | 0 |
| QoS classification ACEs | 3000 | 3000 |
| Security ACEs | 3000 | 3000 |
| Security ACEs | 1024 | 1024 |
| Input Microflow policer ACEs | 256000 | 0 |
| Output Microflow policer ACEs | 256000 | 0 |
| FSPAN ACEs | 256 | 256 |
| Control Plane Entries | 512 | 512 |
Cisco SDM Template Types
SDM template types can be selected to provide maximum system usage depending on how the switch is used. These include the following switch SDM templates:
- Default Template – balances system resources for all functions and is the default template configured in the device.
- Access Template – optimizes the system resources to support a high number of Access Control Lists (ACLs).
- VLAN Template – disables routing and allows for the maximum number of unicast MAC addresses. It is usually used for a Layer 2 switch with no routing support in hardware, maximizing VLAN configuration on the switch.
- Routing Template – maximizes system resources for IPv4 unicast routing on the switch. A router or aggregator is usually necessary at the center of the network.
- Dual IPv4 and IPv6 Template – enables the switch to operate in dual-stack environments by supporting IPv4 and IPv6 routing. It has three types:
- Default – balances the IPv4 and IPv6 Layer 2 and Layer 3 functions.
- Routing- optimizes usage for IPv4 and IPv6 routing, along with IPv4 policy-based routing.
- VLAN – ensures maximum utilization for IPv4 and IPv6 VLANs.
SDM Template Verification
The ‘show sdm prefer’ command verifies the current SDM template configured on the switch. The configuration below shows the desktop default template on a Cisco 3560 switch.
Switch>en 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: 0.5K number of IPv4/MAC security aces: 1K
SDM Template Configuration
The command ‘sdm prefer <template>’ is used to configure an SDM template on a switch. The command is entered in the global configuration mode. The context of help can be used to check the supported SDM templates:
Switch(config)#sdm prefer ? access Access bias default Default bias dual-ipv4-and-ipv6 Support both IPv4 and IPv6 routing Unicast bias vlan Vlan bias
For example, if the switch is required to support dual IPv4 and IPv6 traffic and balanced Layer 2 and Layer 3 functions, the configuration will be:
Switch(config)#sdm prefer dual-ipv4-and-ipv6 default 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. Switch(config)# Switch(config)#end Switch# %SYS-5-CONFIG_I: Configured from console by console Switch#reload
The ‘reload’ command reloads the switch for the new SDM template to take effect. Now, when we do a ‘show sdm prefer’ after the switch reloads, the template is changed to “desktop IPv4 and IPv6 default”.
Switch> Switch>en Switch#show sdm prefer The current template is "desktop IPv4 and IPv6 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: 2K number of IPv4 IGMP groups + multicast routes: 1K number of IPv4 unicast routes: 3K number of directly-connected IPv4 hosts: 2K number of indirect IPv4 routes: 1K number of IPv6 multicast groups: 1.125k number of directly-connected IPv6 addresses: 2K number of indirect IPv6 unicast routes: 1K number of IPv4 policy based routing aces: 0 number of IPv4/MAC qos aces: 0.5K number of IPv4/MAC security aces: 1K number of IPv6 policy based routing aces: 0 number of IPv6 qos aces: 0.625k number of IPv6 security aces: 0.5K
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