Quick Answer
The answer is the IRB interface. In an EVPN-VXLAN fabric, Integrated Routing and Bridging (IRB) interfaces are required for inter-subnet routing because they serve as the Layer 3 gateway within the VXLAN overlay, terminating both the bridge domain and the routing instance to enable traffic to move between different VLANs or VXLANs. On the JNCIA-Junos exam, this concept tests your understanding of how Juniper QFX switches handle overlay routing—a common trap is confusing IRB with a standard routed VLAN interface (RVI) or assuming a simple Layer 3 interface on the physical port can route VXLAN traffic. Remember that IRB interfaces are the only way to bridge and route simultaneously in an EVPN-VXLAN design. A helpful memory tip: IRB stands for “I Route and Bridge,” meaning it does both jobs in one interface, unlike a plain routed interface that only routes.
This JNCIA-JUNOS practice question tests your understanding of networking fundamentals. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A company is deploying an EVPN-VXLAN fabric with Juniper QFX switches. To provide inter-subnet routing, which interface type must be configured?
Physical interface with vlan-tagging
Why wrong: Handles VLANs but not routing.
VXLAN tunnel endpoint (VTEP)
Why wrong: VTEP is used for VXLAN encapsulation, not routing.
IRB interface
IRB provides Layer 3 gateway for VLANs.
Loopback interface
Why wrong: Loopback is used for OSPF/BGP peering, not for VLAN routing.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
IRB interface
In an EVPN-VXLAN fabric, Integrated Routing and Bridging (IRB) interfaces are required to provide inter-subnet routing. IRB interfaces act as Layer 3 gateways within the VXLAN overlay, enabling routing between different VLANs/VXLANs by terminating both the bridge domain and the routing instance. Without IRB, traffic cannot be routed between subnets in the EVPN-VXLAN fabric.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Physical interface with vlan-tagging
Why it's wrong here
Handles VLANs but not routing.
VXLAN tunnel endpoint (VTEP)
Why it's wrong here
VTEP is used for VXLAN encapsulation, not routing.
IRB interface
Why this is correct
IRB provides Layer 3 gateway for VLANs.
Related concept
Read the scenario before looking for a memorised answer.
Loopback interface
Common exam traps
The trap here is that candidates often confuse VTEPs (which handle tunneling) with the routing function, mistakenly thinking that configuring a VTEP alone enables inter-subnet routing, when in fact an IRB interface is required to act as the Layer 3 gateway.
Detailed technical explanation
IRB interfaces in Junos are configured under the bridge domain or routing-instance hierarchy, and they are assigned an IP address that serves as the default gateway for hosts in that subnet. In EVPN-VXLAN, the IRB interface is associated with a VNI (VXLAN Network Identifier) and uses the anycast gateway feature (RFC 7432) to provide active-active gateway redundancy across multiple leaf switches. A common real-world scenario is when hosts in VLAN 100 (VNI 100) need to communicate with hosts in VLAN 200 (VNI 200); the IRB interfaces on the leaf switches perform the routing, while VTEPs handle the encapsulation.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
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FAQ
Networking Fundamentals — This question tests Networking Fundamentals — Read the scenario before looking for a memorised answer..
The correct answer is: IRB interface — In an EVPN-VXLAN fabric, Integrated Routing and Bridging (IRB) interfaces are required to provide inter-subnet routing. IRB interfaces act as Layer 3 gateways within the VXLAN overlay, enabling routing between different VLANs/VXLANs by terminating both the bridge domain and the routing instance. Without IRB, traffic cannot be routed between subnets in the EVPN-VXLAN fabric.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This JNCIA-JUNOS practice question is part of Courseiva's free Juniper Networks 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 JNCIA-JUNOS exam.
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