Summary

To route between VLANs, you need an RP. When setting up routing between VLANs, first create your VLANs and assign switch ports to them; second, create your trunks; third, configure routing. An RP can be internal or external. If the RP is external and has a trunk connection to a switch, it is called a router-on-a-stick. This type of RP is configured using subinterfaces. For an internal RP, a Catalyst switch supports two routing interfaces: routed and SVI. An SVI is typically used and is created with the interface vlan command.

MLS allows Layer 2 and Layer 3 hardware switching to exist in the same chassis. The first packet is routed in software and all other packets in the same connection are rewritten in hardware and switched at Layer 2 speeds. The source MAC, destination MAC, and CRC in the frame are rewritten and the IP TTL field and CRC are rewritten.

NetFlow switching is a Cisco-proprietary form of route caching. This type of switching has the RP and the ASICs work together to cache and switch packets. With centralized switching, all Layer 2 and Layer 3 switching information is maintained in a central location in the switch. With distributed switching, each port or module contains part of the switching tables and can make switching decisions locally.

Cisco's CEF is an example of topology-based switching. This type of switching uses a FIB. A FIB contains information from the routing table. Cisco's CEF also has an adjacency table (neighboring devices) and a TCAM table (contains connection information). The combination of these tables helps CEF perform MLS. By default, CEF is enabled on all of Cisco's Catalyst switches it cannot be disabled on the 6500. CEF can load balance traffic to a destination across a maximum of six links.