Know the difference between an internal and an external route processor. An external route processor is a standard router that is routing between VLANs. An external router can accept packets across a trunk terminating at a single Ethernet interface or it can have several connections, one per VLAN. The second method is required if there are only 10Mb Ethernet interfaces available, because you can not configure trunks on standard Ethernet.
An internal route processor is a special card inside the switch that routes between VLANs. Once connected internally to the route processor, you can configure it in a similar fashion to the external processor/router, as it will run IOS. Modern layer 3 switches with an intelligent matrix run IOS and can be configured in the same way.
Know how to configure VLANs on each of the routers. On an internal route processor, the router has VLAN interfaces as opposed to the Ethernet or serial interfaces found on an external router. The interfaces are accessed in the same fashion, but on an internal router, each VLAN interface gets an IP address and the no shut command must be issued to activate the interface.
On an external router, you must select the appropriate FastEthernet or Gigabit Ethernet interface and create subinterfaces, preferably labeling them the same as the VLAN that will reside there. Configure each subinterface with the appropriate encapsulation and IP address and then issue the no shut command on the physical interface.
Know how to configure routing on the router and on the switch. Both internal and external route processors can be configured to route packets from one network to another based on routing protocol information. To configure a dynamic routing protocol, you must enter global configuration mode and use the router command followed by routing-protocol-specific information. No routing protocol may be needed if all VLANs in your network have an interface on the route processor and there are no external links.
To configure routing on a switch, you must configure a default gateway on the switch. Use the command set ip route to accomplish this, pointing to an IP address that can forward packets to other networks, something like a router interface.