Topology-Based Switching

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.

Author Aaron

Aaron knows networks. He's been involved in building and supporting world-class data networks for the past 10 years - from international cloud service providers to Fortune 50 data centers. Aaron consults independently and is focused on building the best training platform available.

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