Explanation:
* X = 0
* Y = 0
* Z = 1
Understanding MPLS Label Headers
# What is MPLS (Multiprotocol Label Switching)?
* MPLS is a high-performance forwarding technology that replaces IP lookups with label switching.
* Packets are forwarded based on labels instead of destination IP addresses.
* MPLS labels are stacked when passing through multiple hops.
# MPLS Label Stack StructureEach MPLS label has four fields:
* Label - 20-bit identifier used for forwarding.
* EXP (Experimental Bits / Traffic Class) - 3-bit field used for QoS (Quality of Service).
* S (Bottom of Stack) - 1-bit flag that indicates whether this is the last (bottom) label in the stack.
* TTL (Time-To-Live) - 8-bit field to prevent loops.
Understanding the EXP Fields (X, Y, Z) in the Figure
* The image shows a packet with three MPLS labels.
* Each label has an EXP field (X, Y, Z) representing the QoS bits.
* By default, MPLS EXP bits are copied from the top label to lower labels unless modified by QoS policies.
* If no QoS policy modifies the EXP bits, they remain the default value of 0.
* The bottom label in the stack (Label 3) often has an EXP value of 1 to indicate specific QoS policies.
Why Are the Answers X = 0, Y = 0, Z = 1?
# X = 0 (Default EXP for Label 1, the top label in the stack).# Y = 0 (EXP for Label 2, unchanged from the default value).# Z = 1 (EXP for Label 3, indicating a QoS setting applied to the bottom label).
Real-World Application:
* MPLS QoS (Quality of Service): EXP values determine packet priority in Service Provider networks.
* Traffic Engineering (TE): MPLS labels guide packets through optimized paths, ensuring low-latency services.
* Enterprise WAN Optimization: MPLS traffic is prioritized for critical applications like VoIP, Video Conferencing, and Cloud Services.
# Reference: Huawei HCIE-Datacom Guide - MPLS Label Stack and QoS EXP Field Processing