CCNA 3 v6.0 Study Material – Chapter 2: Scaling VLANs

Chapter 2 – Sections & Objectives

2.1 VTP, Extended VLANs, and DTP

Configure enhanced inter-switch connectivity technologies.

2.2 Troubleshoot Multi-VLAN Issues

Troubleshoot issues in an inter-VLAN routing environment.

2.3 Layer 3 Switching

Implement inter-VLAN routing using Layer 3 switching to forward data in a small to medium-sized business LAN.


2.1 VTP, Extended VLANs, and DTP

VTP Concepts and Operation

  • VLAN trunking protocol (VTP) allows a network administrator to manage VLANs on a switch configured as a VTP server.
  • VTP stores VLAN configurations in a database called vlan.dat.
  • A switch can be configured in one of three VTP modes:
  • Server
  • Client
  • Transparent
  • VTP includes three types of
  • advertisements:
  • Summary
  • Advertisement request
  • Subset advertisements

  • VTP has 3 versions
  • The show vtp status privileged EXEC command displays the VTP status.

  • The configuration revision number is used when determining whether a switch should keep its existing VLAN database, or overwrite it with the VTP update sent by another switch.
  • When a switch is added to a network, ensure that it has a default VTP configuration.

VTP Configuration

  • There are 5 steps to VTP configuration:
  • Configure the VTP Server.
  • Configure the VTP Domain Name and Password.
  • Configure the VTP Clients.
  • Configure VLANs on the VTP Server.
  • Verify the VTP Clients have received the new VLAN information.


Extended VLANs

  • Normal range VLANs are identified by a VLAN ID between 1 and 1005.
  • Extended range VLANs are identified by a VLAN ID between 1006 and 4094.
  • VTP does not learn extended range VLANs.
  • Creating a VLAN
  • In addition to entering a single VLAN ID, a series of VLAN IDs can be entered that are separated by commas, or as range of VLAN IDs separated by hyphens.

  • Assigning Ports to VLANs
  • After creating a VLAN, the next step is to assign ports to the VLAN.

  • Verifying VLAN Information
  • VLAN configurations can be validated using Cisco IOS show commands.
  • Configuring Extended VLANs
  • To configure an extended VLAN on a 2960 switch it must be set to VTP transparent mode.

Dynamic Trunking Protocol

  • DTP
  • DTP manages trunk negotiation only if the port on the neighbor switch is configured in a trunk mode that supports DTP.
  • Turn off DTP on interfaces on a Cisco switch that is connected to devices that do not support DTP.
  • To enable trunking from a Cisco switch to a device that does not support DTP, use the switchport mode trunk and switchport nonegotiate interface configuration mode commands.
  • There are 5 commands to support different trunking modes:
  • switchport mode access
  • switchport mode dynamic auto
  • switchport mode dynamic desirable
  • switchport mode trunk
  • switchport nonegotiate


2.2 Troubleshoot Multi-VLAN Issues

Inter-VLAN Configuration Issues

  • To delete a VLAN, use the no vlan vlan-id global configuration mode command.
  • If a switch port is not configured for the correct VLAN, devices configured on that VLAN cannot connect to the router interface.
  • When a problem is suspected with a switch configuration, use the various verification commands to examine the configuration and identify the problem.

  • Interface Issues
  • When enabling inter-VLAN routing on a router, one of the most common configuration errors is to connect the physical router interface to the wrong switch port.
  • Verify Routing Configuration
  • With router-on-a-stick configurations, a common problem is assigning the wrong VLAN ID to the subinterface.
  • Using the show interfaces and the show running-config commands can be useful in troubleshooting this type of issue.


IP Addressing Issues

  • IP Addresses and Subnet Masks
  • For inter-VLAN routing to operate, a router must be connected to all VLANs, either by separate physical interfaces or by subinterfaces.
  • Each interface, or subinterface, must be assigned an IP address that corresponds to the subnet to which it is connected.
  • Use the show running-config and show ip interface commands to verify IP address and subnet masks.


VTP and DTP Issues

  • Troubleshoot VTP Issues
  • There are 5 common problems with VTP:
  • Incompatible VTP Versions
  • VTP Password Issues
  • Incorrect VTP Domain Name
  • All Switches Set to Client Mode
  • Incorrect Configuration Revision
  • Number
  • Troubleshoot DTP Issues
  • there are three common problems
  • associated with trunks.
  • Trunk mode mismatches
  • Allowed VLANs on trunks
  • Native VLAN mismatches


2.3 Layer 3 Switching

Layer 3 Switching Operation and Configuration

  • Layer 3 Switching
  • Modern enterprise networks use multilayer switches to achieve high-packet processing rates using hardware-based switching.
  • Catalyst multilayer switches support the following types of Layer 3 interfaces:
  • Routed port
  • Switch virtual interface (SVI)
  • Inter-VLAN Routing and SVIs
  • Routing can be transferred to the core and the distribution layers (and sometimes even the access layer) without impacting network performance.
  • An SVI can be created for any VLAN that exists on the switch.
  • SVIs are created the first time the VLAN interface configuration mode is entered for a particular VLAN SVI.

  • Inter-VLAN Routing with Routed Ports
  • A routed port is a physical port that
  • acts similarly to an interface on a router.
  • A routed port is not associated with
  • a particular VLAN.
  • Routed ports on a Cisco IOS switch do
  • not support subinterfaces.
  • Routed ports are used for point-to-point
  • links.
  • To configure routed ports, use the
  • no switchport interface configuration mode
  • command on the appropriate ports.


Troubleshoot Layer 3 Switching

  • Layer 3 Switch Configuration Issues
  • Check  the following configurations for accuracy:
  • VLANs – VLANs must be defined across all the switches. VLANs must be enabled on the trunk ports. Ports must be in the right VLANs.
  • SVIs – SVIs must have the correct IP address or subnet mask. SVIs must be up. Each SVI must match with the VLAN number.
  • Routing – Routing must be enabled. Each interface or network should be added to the routing protocol, or static routes entered, where appropriate.
  • Hosts – Hosts must have the correct IP address or subnet mask. Hosts must have a default gateway associated with an SVI or routed port.

2.4 Chapter Summary


  • VLAN Trunking Protocol (VTP) reduces administration of VLANs in a switched network. A switch configured as the VTP server distributes and synchronizes VLAN information over trunk links to VTP-enabled switches throughout the domain.
  • The three VTP modes are Server, Client and Transparent.
  • The configuration revision number is used when determining whether a VTP switch should keep or update its existing VLAN database. A switch will overwrite its existing VLAN database if it receives a VTP update from another switch in the same domain with a higher configuration revision number. Therefore, when a switch is being added to a VTP domain it must have the default VTP configuration or a lower configuration revision number than the VTP server.
  • Troubleshooting VTP can also involve dealing with errors caused by incompatible VTP versions and incorrectly configured domain names or passwords.
  • Trunk negotiation is managed by the Dynamic Trunking Protocol (DTP), which operates on a point-to-point basis between network devices. DTP is a Cisco proprietary protocol that is automatically enabled on Catalyst 2960 and Catalyst 3560 Series switches. A general best practice when a trunk link is required is to set the interface to trunk and nonegotiate. On links where trunking is not intended, DTP should be turned off.
  • When troubleshooting DTP, problems can be related to trunk mode mismatches, allowed VLANS on a trunk, and native VLAN mismatches.
  • Layer 3 switching using Switch Virtual Interfaces (SVIs) is a method of inter-VLAN routing that can be configured on Catalyst 2960 switches. An SVI with appropriate IP addressing is configured for each VLAN and provides Layer 3 processing for packets to or from all switch ports associated with those VLANs.
  • Another method of Layer 3 inter-VLAN routing is using routed ports. A routed port is a physical port that acts similarly to an interface on a router. Routed ports are mostly configured between switches in the core and distribution layer.
  • Troubleshooting inter-VLAN routing with a router or a Layer 3 switch are similar. Common errors involve VLAN, trunk, Layer 3 interface, and IP address configurations.


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