Optimizing System Resources on a Catalyst Switch via SDM

By using Switch Database Management (SDM) templates, you can configure memory resources in the switch to optimize support for specific features, depending on how the switch is used in your network. You can select one of four templates to specify how system resources are allocated. You can then approximate the maximum number of unicast MAC addresses, Internet Group Management Protocol (IGMP) groups, quality of service (QoS) access control entries (ACEs), security ACEs, unicast routes, multicast routes, subnet VLANs (routed interfaces), and Layer 2 VLANs that can be configured on the switch.

The four templates prioritize system memory to optimize support for these types of features:

• QoS and security ACEs—The access template might typically be used in an access switch at the network edge where the route table sizes might not be substantial. Filtering and QoS might be more important because an access switch is the entry to the whole network.
• Routing—The routing template maximizes system resources for unicast routing, typically required for a router or aggregator in the center of a network.
• VLANs—The VLAN template disables routing and supports the maximum number of unicast MAC addresses. It would typically be selected for a switch used as a Layer 2 switch.
• Default—The default template gives balance to all functionalities (QoS, ACLs, unicast routing, multicast routing, VLANs and MAC addresses).

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Changing the MAC Address Aging Time

Dynamic addresses are source MAC addresses that the switch learns and then ages when they are not in use. You can change the aging time setting for all VLANs or for a specified VLAN.  Setting too short an aging time can cause addresses to be prematurely removed from the table. Then when the switch receives a packet for an unknown destination, it floods the packet to all ports in the same VLAN as the receiving port. This unnecessary flooding can impact performance. Setting too long an aging time can cause the address table to be filled with unused addresses, which prevents new addresses from being learned.

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Understanding and Configuring SNMP on Cisco 3550

SNMP is an application-layer protocol that provides a message format for communication between managers and agents. The SNMP system consists of an SNMP manager, an SNMP agent, and a MIB. The SNMP manager can be part of a network management system (NMS) such as CiscoWorks. The agent and MIB reside on the switch. To configure SNMP on the switch, you define the relationship between the manager and the agent.

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