Layer 3 Switch Processing

• process switching – requires the CPU to be personally involved with every forwarding decission
• fast switching – still uses a CPU but after a packet has been forwarded, infromation about how to reach the destination is stored in a fast-switching cache
• CEF – optimizing the router to make it able to forward more packets faster

CEF

When CEF came we started do think about control plane and data plane in our network devices. CEF is build in hardware of our devices (ASICS) – it is the data plane. CEF is build from two tables – FIB where routing info is stored and adjacency table where ARP table and next hop interfaces are stored. Control plane is the CPU of the network devices. Concept is easy. The routing table and arp table is synchronized with the ASICS down in hardware. When the packet flows through the router it is switched based on information in the hardware. The router also doesnt need to do double lookup – to find if destination is in table and then behind what interface is next hop ip. This brings wire speed switching and routing.