Question 743 of 1,840
mediumMultiple SelectObjective-mapped
MPLS Label Operations: Push, Swap, Pop, and Penultimate Hop Popping
Which two statements about MPLS label operations are true? (Choose two.)
Quick Answer
The correct answer is that the egress LSR removes the label before forwarding the IP packet, because in MPLS label operations, the egress router performs a pop to strip the final label, leaving only the native IP packet for onward routing. This contrasts with the ingress LSR, which performs a push to impose the initial label, and intermediate LSRs that execute a swap—replacing the incoming label with a new outgoing label. On the ENCOR 350-401 exam, this topic tests your understanding of the label lifecycle across the MPLS domain, often appearing in multiple-choice questions that require distinguishing which router performs which operation. A common trap is confusing the egress pop with the penultimate hop popping (PHP) feature, where the second-to-last router pops the label so the egress receives a pure IP packet. Remember the mnemonic: Ingress Pushes, Transit Swaps, Egress Pops—and PHP lets the penultimate do the pop early.
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
✓
The ingress LSR imposes a label onto the packet.
In MPLS, the ingress LSR imposes (pushes) a label onto the packet. At each intermediate LSR, the label is swapped (the incoming label is replaced with an outgoing label). The egress LSR removes (pops) the label before forwarding the IP packet. Penultimate Hop Popping (PHP) is a feature where the penultimate router pops the label, so the egress router receives only an IP packet. Option C is incorrect because the egress LSR always pops the label, not pushes. Option D is incorrect because label imposition occurs only at the ingress, not at every LSR. Option E is incorrect because label swapping is the action at transit LSRs, not label imposition.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The ingress LSR imposes a label onto the packet.
Why this is correct
Correct because the ingress LSR pushes the initial label onto the packet.
- ✓
The egress LSR removes the label before forwarding the IP packet.
Why this is correct
Correct because the egress LSR pops the label to restore the original IP packet.
- ✗
The egress LSR pushes a new label onto the packet.
Why it's wrong here
Incorrect because the egress LSR pops the label, not pushes.
- ✗
Each LSR in the LSP performs label imposition.
Why it's wrong here
Incorrect because label imposition occurs only at the ingress LSR.
- ✗
Transit LSRs perform label imposition.
Why it's wrong here
Incorrect because transit LSRs perform label swapping, not imposition.
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Same concept, more angles
1 more way this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which two statements about MPLS label operations are true? (Choose two.)
medium- ✓ A.The ingress LSR performs a label push operation.
- ✓ B.Transit LSRs perform a label swap operation.
- C.The egress LSR performs a label push operation.
- D.PHP (Penultimate Hop Popping) causes the egress LSR to pop the label.
- E.The egress LSR always performs an IP lookup after label removal.
Why A: In MPLS, the ingress LSR pushes a label onto the packet, and transit LSRs swap the incoming label with an outgoing label based on the LFIB. PHP removes the label before the egress LSR, so the egress LSR does not perform a label lookup. The egress LSR forwards based on the IP header after label removal.
Last reviewed: Jun 18, 2026
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