Which option is the default switching mode and uses information from tables that are built by the CPU, such as the routing table and the ARP table, to build hardware-based tables that are known as the FIB and adjacency tables?
- process switching
- program-layered switching
- Cisco Express Forwarding
- fast switching
Explanation: Cisco Express Forwarding (CEF) is identified as the default switching mode for Cisco routers. It is a topology-based switching mechanism that is significantly less CPU-intensive than process or fast switching because it pre-builds forwarding information before traffic actually arrives.
CEF functions by taking information from control plane tables built by the CPU—specifically the IP routing table and the ARP table—to construct two specialized hardware-based tables:
- Forwarding Information Base (FIB): Derived from the IP routing table, the FIB contains a mirrored set of the routing information and is optimized for fast destination lookups.
- Adjacency Table: Derived from the ARP table, this table stores the Layer 2 next-hop addresses and pre-computed frame header rewrite information for all entries in the FIB.
By using these tables, CEF allows the data plane to make hardware-based forwarding decisions for every packet in a data flow, including the very first packet, without needing to involve the CPU for a software lookup.
Related exam: Modules 1 – 7: Checkpoint Exam: Network Switching Answers (CCNP ENCOR v9)
