Monday, September 29, 2008

SDM - Switch Database Modifier

SDM is used for memory management on your switches. Anytime you hear the "Memory Management"  keyword  that means SDM in your switches.

Switches comes with a finite amount of memory, and, you may need to optimize your switch  to support all L2/L3 memory requirements for a specific type of traffic.

It brings us many possibilities of how we´re going to use the switch memory! But, the real question is... how to do it?!

We got default profiles, just keep in mind, no matter which profile you choose, it won´t break your lab, on the other hand, it can bring serious damages to a real network! So, always, plan before configuring anything!

The SDM Templates are used to optimize the switch for specific features, for IPv4 we have:

  • Access — The access template maximizes system resources for access control lists (ACLs) to accommodate a large number of ACLs.
  • Default — The default template gives balance to all functions.
  • 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 Layer 2 switch.

So, anytime we change the SDM, which by the way, it´s the only command about Memory Management, we MUST reload the switch in order for to take effect! This is very important! If you do not reload the switch, and the proctor issue a show sdm and it shows it´ll be "routing"  on next reload, you lost your section points!

The configuration is pretty straight-forward, for example, to optimize routing, we use the global configuration command sdm prefer routing and that´s it, check this example:

Switch(config)# sdm prefer vlan
Switch(config)# end
Switch# reload
Proceed with reload? [confirm]

DO NOT forget to reload! Otherwise it won´t take effect! If you issue a show sdm before the reload, your output will look pretty much like this one:

Switch# show sdm prefer
 The current template is "desktop routing" 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:            3K
  number of igmp groups + multicast routes:   1K
  number of unicast routes:                   11K
    number of directly connected hosts:       3K
    number of indirect routes:                8K
  number of qos aces:                         512
number of security aces:                    1K
 On next reload, template will be "desktop vlan" template.

Not difficult at all right?! More information can be found at:

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