CCNP SP MPLS FAQ: Cisco Express Forwarding
Q1. Name the two components of CEF.
Q2. Name the three most common packet switching methods in Cisco IOS.
Q3. Why does MPLS use CEF?
Q4. What is the adjacency table used for?
Q5. What fields of the IP header does CEF use to load-balance IP packets?
Q6. How does CEF perform equal and unequal cost load balancing?
Q7. How does a prefix in the CEF table get the imposed label stack?
Q8. How is load balancing of labeled packets performed in Cisco IOS?
Q9. Name two reasons not to use CEF per-packet load balancing.
Answer: Two reasons for not using CEF per-packet load balancing are these:
- Receipt of out-of-sequence packets, resulting in reordering of the packets or dropping of the packets
- Jitter (variable delay)
Q10. Name two huge differences between the fast switching and the CEF switching methods.
Answer: Fast switching and CEF switching are different in the following two ways:
- Fast switching uses an on-demand route cache, whereas the CEF switching table is prebuilt.
- The CEF table holds the MPLS label information to label IP packets before switching them out of the router; fast switching does not.