MPLS Packet Header JN0-364 Practice Questions (Page 2)

Questions 6–10

1. 6application · medium

   A service provider is configuring QoS in its MPLS core. The provider wants to ensure that voice traffic receives priority queuing at every LSR. The PE router marks voice packets with EXP = 5. What must the core LSRs do to honor this marking?

   • ASet the EXP field to 0 on all core links to ensure uniform treatment.
   • BIgnore the EXP field and use the IP DSCP value instead.
   • CUse the EXP field to classify packets into the appropriate forwarding queue.
   • DRewrite the EXP field to a lower value to prevent voice from monopolizing the queue.
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2. 7foundation · easy

   Which reserved MPLS label value is used for IPv4 explicit null?

   • A0
   • B1
   • C2
   • D3
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4. 8foundation · easy

   In the MPLS shim header, what is the purpose of the S bit?

   • AIt indicates whether the packet is IPv4 or IPv6.
   • BIt indicates the bottom of the label stack.
   • CIt signals the start of a new label stack.
   • DIt carries the class-of-service information.
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5. 9application · medium

   A network engineer is troubleshooting an MPLS network and notices that traceroute from a customer edge device does not show the hops inside the MPLS core. The engineer suspects that the TTL of the MPLS label is not being decremented as expected. Which behavior would cause the traceroute to show the core hops?

   • AThe egress PE copies the MPLS TTL back to the IP TTL, but only if the S bit is set.
   • BThe LSRs use the IP TTL instead of the MPLS TTL for loop prevention.
   • CThe ingress PE copies the IP TTL into the MPLS TTL, and each LSR decrements the MPLS TTL.
   • DThe ingress PE sets the MPLS TTL to 255 and never decrements it.
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6. 10foundation · easy

   How does the MPLS TTL field support traceroute functionality?

   • AIt stores the IP address of each hop in the label stack.
   • BIt is copied to the IP header at each hop for tracing.
   • CIt is incremented at each hop, and the final value is reported to the source.
   • DIt is decremented at each hop, and when it reaches 0, an ICMP TTL exceeded message is sent back to the source.
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