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Intervlan Routing using layer 3 switch

As far as I know, layer 3 switch in CEF forwarding maintains FIB and adjacency tables. Fib table is constructed from routing table and gives next hop info while adjacency table is used for creating layer 2 header. Consider an example where host in vlan 10 wants to talk to host in vlan 20. Packet enters at layer 3 switch and it does FIB look up for the next hop which would SVI for vlan 20. After that it does adj look up for layer 2 header and forwards the packet. My question why is FIB look up required, it can directly forward the packet, looking at adj table as it has entry for the destination IP address and corresponding mac address.


Intervlan Routing using layer 3 switch

Because the adjacency table is derived from the ARP cache and CEF is an improvement over MLS by incorporating FIB and Adjacency table.

FIB and Adjacency table is an organizational mechanism that has the same information as the ARP and route table. This incorporation is for faster look up by the data plane.

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