Ethernet and Switching

Inter-VLAN Routing

Learn why separate VLANs need Layer 3 routing, how router-on-a-stick connects them, and how trunk settings control VLAN traffic.

Intermediate12 min read
Ethernet and Switching lessonNetworkingPractice

UNTIMED COACHING

Practice before the pressure

Use feedback to correct the model, not merely memorize an option position.

GUIDED PRACTICE

Practice the lesson questions

Answer normal lesson questions without a timer. Every answer includes an explanation, and incorrect answers can be tried again before continuing.

CONCEPT MODELS

See the lesson as a system

Use these visual guides to connect the key ideas before answering the questions.

Inter-VLAN Routing PathSeparate VLANs use a trunk to reach router subinterfaces for Layer 3 forwarding.
Inter-VLAN Routing PathTwo VLAN segments connect through a trunk to matching router subinterfaces, which exchange traffic between them.
VLAN 10Separate Layer 2 segment
VLAN 20Separate Layer 2 segment
802.1Q trunkCarries selected VLAN traffic
Subinterface for VLAN 10Provides the VLAN 10 gateway
Trunk Eligibility ChecksA VLAN crosses a trunk only when it is available and permitted on that port.
Trunk Eligibility ChecksVTP availability and the individual trunk allowed list lead to forwarding eligibility.
VLAN availableKnown through VTP and enabled
Port allowed listIncludes the VLAN on this trunk
Traffic crossesThe trunk forwards that VLAN
Traffic excludedThis trunk does not forward it
Native VLAN AgreementThe native VLAN identifies untagged trunk traffic and must have matching settings at both ends.
Native VLAN AgreementBoth trunk endpoints compare native VLAN settings before interpreting untagged traffic.
Trunk endpoint ANative VLAN setting
Trunk endpoint BNative VLAN setting
Matching identityHandles untagged frames consistently
Different identityMisclassifies untagged frame traffic