350-501 Networking Practice Question
Exhibit
Refer to the exhibit. R1# show mpls ldp bindings label bindings: 5 label binding: 10.1.1.1/32, label 16 label binding: 10.2.2.2/32, label 17 label binding: 10.3.3.3/32, label 18 label binding: 10.4.4.4/32, label 19 label binding: 10.5.5.5/32, label 20 R1# show mpls forwarding-table Local Outgoing Prefix Bytes Label Outgoing Next Hop Label Label or Tunnel Id Switched interface 16 Pop Label 10.1.1.1/32 0 Gi0/0 192.168.1.2 17 18 10.2.2.2/32 0 Gi0/0 192.168.1.2 18 19 10.3.3.3/32 0 Gi0/0 192.168.1.2 19 20 10.4.4.4/32 0 Gi0/0 192.168.1.2 20 Untagged 10.5.5.5/32 0 Gi0/0 192.168.1.2
Based on the exhibit, which prefix is NOT reachable via MPLS forwarding?
⚠ Common exam trap
Cisco often tests the distinction between prefixes that have LDP label bindings versus those that are simply present in the routing table, trapping candidates who assume all IGP routes are automatically MPLS-switched without verifying the label bindings.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
10.5.5.5/32
(10.5.5.5/32) is correct because the exhibit shows that the LDP label bindings are only present for prefixes 10.1.1.1/32, 10.2.2.2/32, and 10.3.3.3/32. The prefix 10.5.5.5/32 is not in the LDP label information base (LIB), meaning no MPLS label has been assigned to it, so it cannot be forwarded via MPLS and must be forwarded using standard IP routing instead.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
10.1.1.1/32
Why it's wrong here
It has Pop Label, which is valid for MPLS forwarding.
- ✗
10.3.3.3/32
Why it's wrong here
It has an outgoing label of 19, so it is forwarded via MPLS.
- ✗
10.2.2.2/32
Why it's wrong here
It has an outgoing label of 18, so it is forwarded via MPLS.
- ✓
10.5.5.5/32
Why this is correct
The outgoing label is Untagged, so MPLS forwarding is not applied, likely causing packet drop.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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