350-401 Question 71
Select 2A network engineer is troubleshooting a routing and switching issue in a Cisco Enterprise network. The issue involves slow packet forwarding due to suboptimal path selection. During the analysis, the engineer decides to verify the data structures used for packet forwarding in a Cisco device running CEF (Cisco Express Forwarding). Which of the following components are directly utilized by CEF to optimize packet forwarding decisions?
- A
Forwarding Information Base (FIB)
- B
Routing Information Base (RIB)
- C
Content Addressable Memory (CAM)
- D
Ternary Content Addressable Memory (TCAM)
- E
Adjacency Table
Show answer and explanation
Correct answers: A, E
Explanation
Cisco Express Forwarding (CEF) uses the Forwarding Information Base (FIB) for optimized Layer 3 packet forwarding decisions. The FIB is derived from the Routing Information Base (RIB) but is specifically designed for fast lookups. The Adjacency Table complements the FIB by maintaining Layer 2 adjacency information (e.g., next-hop MAC addresses) for efficient forwarding. CAM and TCAM are used for different purposes, such as Layer 2 switching and advanced filtering, and are not part of the core CEF mechanism.
- A. Correct.
The Forwarding Information Base (FIB) is a key data structure used by CEF to store precomputed routing information for efficient packet forwarding.
- B. Incorrect.
The Routing Information Base (RIB) is a broader table used by routing protocols to manage routes but is not directly utilized by CEF for packet forwarding. Instead, the FIB is derived from the RIB.
- C. Incorrect.
Content Addressable Memory (CAM) is used for Layer 2 switching decisions, such as MAC address lookups, and is not directly involved in CEF's Layer 3 packet forwarding.
- D. Incorrect.
Ternary Content Addressable Memory (TCAM) is used for advanced access control lists (ACLs) and QoS but is not directly involved in CEF's forwarding process.
- E. Correct.
The Adjacency Table is used by CEF to store information about Layer 2 adjacency relationships (e.g., next-hop MAC addresses) and is essential for packet forwarding.