Layer 3 Sub-interface

Overview

A single physical interface when required to handle multiple VLAN traffic, can be divided into multiple logical interfaces called sub-interfaces.

All sub-interfaces under a physical port will use their parent port for transmitting and receiving data.

Sub-interfaces can be used for various purposes, as for inter-vlan routing to happen when router has only one physical interface, two sub-interfaces each with different IP network can be created under it and data can be routed between them.

Sub-interfaces let you divide a physical interface into multiple logical interfaces that are tagged with different VLAN identifiers. Because VLANs allow you to keep traffic separate on a given physical interface, you can increase the number of interfaces available to your network without adding additional physical interfaces.

Feature Characteristics

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Each subinterface is treated as a separate Layer 3 entity with its own IP address, routing table entries, and configuration.

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Subinterfaces are associated with VLAN IDs (via IEEE 802.1Q tagging), enabling traffic separation on the same physical link.

Benefits

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Reduces the need for multiple physical interfaces.

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Enables multiple IP subnets/VLANs over a single physical link.

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Allows flexible routing between VLANs without external Layer 3 devices.

Limitations

Queuing service policy-maps are not supported on Layer 3 sub-interfaces.