CCNP SP MPLS FAQ: MPLS Architecture
Q1. Name the four fields that are part of a label.
Q2. How many labels can reside in a label stack?
Q3. In which layer does MPLS fit in the OSI reference model?
Q4. Which table does an LSR use to forward labeled packets?
Q5. What type of interfaces in Cisco IOS use the Downstream-on-Demand label distribution mode and the
per-interface label space?
Figure: Per-Interface Label Space
Q6. Why does the MPLS label have a Time To Live (TTL) field?
Q7. Describe some of the drawbacks that you might encounter when using traditional IP routing.
Hop-by-hop forwarding decisions are based on IP destination lookup.
IP lookup is based purely on the destination unicast address.
All packets bound for the same destination follow the same path.
All routers require full routing information to forward packets reliably.
Q8. Why is Policy Based Routing (PBR) unsuitable for engineering traffic in a large network?
Q9. What benefit does the separation of forwarding and control elements, through the use of labels, provide?
Q10. Does every MPLS node need to run an IP routing protocol to exchange IP routing information with other MPLS nodes?
Q11. List the different types of LSRs within an MPLS network.
Q12. Describe the functionality of an Edge-LSR.
Q13. What is a Label Switched Path (LSP) and is it unidirectional or bidirectional?
Q14. Is Cisco Express Forwarding (CEF) necessary on an Edge-LSR?
Q15. Which two tables does the LSR use to hold information that is relevant to the MPLS forwarding component?
Q16. What is the primary difference between the Label Forwarding Information Base (LFIB) and the Label Information Base (LIB)?
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