CCNA – Semester1

Chapter 6 -

Inter – VLAN Routing

CCNA Exploration version 4.0

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Objectives

• Explain how network traffic is routed between

VLANs in a converged network.

• Configure inter-VLAN routing on a router to

enable communications between end-user

devices on separate VLANs

• Troubleshoot common inter-VLAN

connectivity issues.

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Introduction

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Introduction

Inter-VLAN Routing permits computers on separate VLANs

can communicate with each other

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Traditional Inter-VLAN Routing

• In a traditional network that uses multiple VLANs to

segment the network traffic into logical broadcast domains,

routing is performed by connecting different physical router

interfaces to different physical switch ports.

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"Router-on-a-stick" Inter-VLAN Routing

• "Router-on-a-stick" is a type of router configuration in which

a single physical interface routes traffic between multiple

VLANs on a network.

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Switched-based Inter-VLAN Routing

• Some switches can perform Layer 3 functions, replacing the

need for dedicated routers to perform basic routing on a

network. Multilayer switches are capable of performing inter-

VLAN routing.

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Interface and Subinterface

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Interface

• Traditional routing requires routers to have multiple physical

interfaces to facilitate inter-VLAN routing.

• Each interface is also configured with an IP address for the

subnet associated with the particular VLAN that it is

connected to.

• In this configuration, network devices can use the router as a

gateway to access the devices connected to the other

VLANs.

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Interface Configuration

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Subinterface

• To overcome the hardware limitations of inter-VLAN routing

based on router physical interfaces, virtual subinterfaces and

trunk links are used.

• Each subinterface is configured with its own IP address,

subnet mask, and unique VLAN assignment, allowing a

single physical interface to simultaneously be part of multiple

logical networks.

• Functionally, the router-on-a-stick model for inter-VLAN

routing is the same as using the traditional routing model,

but instead of using the physical interfaces to perform the

routing, subinterfaces of a single interface are used.

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Subinterface (cont)

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Subinterface Configuration

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Comparison

Features Physical Interface Subinterface

Port LimitsOne physical interface

per VLAN

One physical interface for

many VLANs

Performance No bandwidth contention Bandwidth contention

Access Ports and

Trunk Ports

Connected to access

mode switch port

Connected to trunk mode

switch port

Cost More expensive Less expensive

ComplexityMore complex

connection configuration

Less complex connection

configuration

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Configure Inter-VLAN Routing

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Configure Traditional Inter-VLAN Routing

Switch Configuration

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Configure Traditional Inter-VLAN Routing

Router Configuration

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Configure Traditional Inter-VLAN Routing

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Configure Router-on-a-Stick Inter-VLAN Routing

Switch Configuration

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Configure Router-on-a-Stick Inter-VLAN Routing

Router Configuration

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Configure Router-on-a-Stick Inter-VLAN Routing

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Some ISSUES with

Inter-VLAN Routing

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Switch Configuration Issues• Switch ports are not configured on the correct VLAN

• No redundant connection or path between the devices

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Router Configuration Issues

• Connect the physical router interface to the wrong switch

port, placing it on the incorrect VLAN and preventing it from

reaching the other VLANs.

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Router Configuration Issues

Router R1 has been configured to use the wrong VLAN on

subinterface F0/0.10, preventing devices configured on

VLAN10 from communicating with subinterface F0/0.10

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IP Addressing Issues

Router R1 has been configured with an incorrect IP address

on interface F0/0. This prevents PC1 from being able to

communicate with router R1 on VLAN10.

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IP Addressing Issues (cont)

PC1 has been configured with an incorrect IP address for the

subnet associated with VLAN10. This prevents PC1 from

being able to communicate with router R1 on VLAN10.

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IP Addressing Issues (cont)

PC1 has been configured with the incorrect subnet mask

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Summary