- A
Ethernet Tag ID
Why wrong: Ethernet Tag identifies service instance.
- B
MAC address of the CE
Why wrong: Not used for ES identification.
- C
Ethernet Segment Identifier (ESI)
Correct identifier.
- D
Route Distinguisher (RD)
Why wrong: RD identifies VPN uniqueness.
Question 847 of 1,000
350-501 MPLS and Segment Routing Practice Question
This 350-501 practice question tests your understanding of mpls and segment routing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
In an EVPN-VPWS (Virtual Private Wire Service) deployment, which identifier is used to uniquely identify an Ethernet Segment for multi-homing?
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
✓
Ethernet Segment Identifier (ESI)
In EVPN-VPWS, the Ethernet Segment Identifier (ESI) uniquely identifies an Ethernet Segment across all multi-homed Provider Edge (PE) nodes. This 10-byte value is used in Designated Forwarder (DF) election and split-horizon filtering to prevent loops when a Customer Edge (CE) is multi-homed to multiple PEs. The ESI is carried in EVPN routes (Type 1 and Type 4) to signal multi-homing membership.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Ethernet Tag ID
Why it's wrong here
Ethernet Tag identifies service instance.
- ✗
MAC address of the CE
Why it's wrong here
Not used for ES identification.
- ✓
Ethernet Segment Identifier (ESI)
Why this is correct
Correct identifier.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Route Distinguisher (RD)
Why it's wrong here
RD identifies VPN uniqueness.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between the Ethernet Tag ID (used for service identification) and the ESI (used for multi-homing segment identification), causing candidates to confuse the two identifiers in EVPN-VPWS contexts.
Detailed technical explanation
How to think about this question
The ESI is a 10-octet field defined in RFC 7432, typically auto-derived from the CE MAC or manually configured. In EVPN-VPWS, the ESI is critical for the Designated Forwarder election process (using the DF election algorithm based on the ESI value) and for implementing split-horizon filtering via the ESI label, which prevents a PE from forwarding traffic back to the same Ethernet Segment. A real-world scenario is a CE dual-homed to two PEs; without a unique ESI, both PEs would forward traffic, causing duplication and loops.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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MPLS and Segment Routing — study guide chapter
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FAQ
Questions learners often ask
What does this 350-501 question test?
MPLS and Segment Routing — This question tests MPLS and Segment Routing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ethernet Segment Identifier (ESI) — In EVPN-VPWS, the Ethernet Segment Identifier (ESI) uniquely identifies an Ethernet Segment across all multi-homed Provider Edge (PE) nodes. This 10-byte value is used in Designated Forwarder (DF) election and split-horizon filtering to prevent loops when a Customer Edge (CE) is multi-homed to multiple PEs. The ESI is carried in EVPN routes (Type 1 and Type 4) to signal multi-homing membership.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
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