Most of Cisco’s switches support the ability to forward frames in hardware based in layer 3 and 4 information. This dramatically improves forwarding performance between network segments and is known as multi-layer switching, or MLS.
Catalyst switches have supported different MLS types over the years, including process switching, route caching, and the most recent – CEF. You can find more details about each under the Switch Forwarding Architectures section on the Inter-VLAN Routing page.
Cisco refers to CEF as a topology-based solution because it uses the switch’s current routing table to pre-populate the entire known networking topology into a special table. That table, known as the FIB or Forwarding Information Base, is a mirror copy of the routing table and is contained in memory for very fast look up.
The longest match in the FIB is used for the layer 3 destination and as the routing table changes, the FIB is updated automatically.
So what’s the takeaway?
Remember that topology-based switching refers to CEF and that it uses the FIB for next-hop look ups.
If you have any questions related to CEF or inter-VLAN switching, feel free to leave a comment below.