350-501 MPLS and Segment Routing Practice Question
In an EVPN-VPWS (Virtual Private Wire Service) deployment, which identifier is used to uniquely identify an Ethernet Segment for multi-homing?
⚠ Common exam trap
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.
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.
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.
- ✗
Route Distinguisher (RD)
Why it's wrong here
RD identifies VPN uniqueness.
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