Chapter 2: Scaling VLANs
Scaling Networks
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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.
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2.1 VTP, Extended VLANs, and DTP
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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:
o Server
o Client
o Transparent
• VTP includes three types of advertisements:
o Summary
o Advertisement request o Subset advertisements
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VTP, Extended VLANs, and DTP
VTP Concepts and Operation (Cont.)
• 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.
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VTP, Extended VLANs, and DTP VTP Configuration
§ There are 5 steps to VTP configuration:
1. Configure the VTP Server.
2. Configure the VTP Domain Name and Password.
3. Configure the VTP Clients.
4. Configure VLANs on the VTP Server.
5. Verify the VTP Clients have received the new VLAN information.
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VTP, Extended VLANs, and DTP 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.
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VTP, Extended VLANs, and DTP Extended VLANs (Cont.)
§ 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.
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VTP, Extended VLANs, and DTP
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
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2.2 Troubleshoot Multi- VLAN Issues
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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.
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Troubleshoot Multi-VLAN Issues
Inter-VLAN Configuration Issues (Cont.)
§ 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.
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Troubleshoot Multi-VLAN Issues
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.
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Troubleshoot Multi-VLAN Issues VTP and DTP Issues
§ Troubleshoot VTP Issues
• There are 5 common problems with VTP: o Incompatible VTP Versions
o VTP Password Issues
o Incorrect VTP Domain Name
o All Switches Set to Client Mode o Incorrect Configuration Revision
Number
§ Troubleshoot DTP Issues
• there are three common problems
associated with trunks.
o Trunk mode mismatches o Allowed VLANs on trunks o Native VLAN mismatches
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2.3 Layer 3 Switching
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Layer 3 Switching
Layer 3 Switching Operation and
Configuration
§ Layer 3 Switching
• Modernenterprisenetworksusemultilayerswitchestoachievehigh-packet
processing rates using hardware-based switching.
• CatalystmultilayerswitchessupportthefollowingtypesofLayer3interfaces:
o Routed port
o Switch virtual interface (SVI)
§ Inter-VLAN Routing and SVIs • Routingcanbetransferredtothecore
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.
• SVIsarecreatedthefirsttimetheVLANinterfaceconfigurationmodeis entered for a particular VLAN SVI.
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Layer 3 Switching
Layer 3 Switching Operation and
Configuration (Cont.)
§ 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.
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Layer 3 Switching
Troubleshoot Layer 3 Switching
§ Layer 3 Switch Configuration Issues
• Check the following configurations for accuracy:
o VLANs – VLANs must be defined across all the switches. VLANs must be enabled on the trunk ports. Ports must be in the right VLANs.
o SVIs – SVIs must have the correct IP address or subnet mask. SVIs must be up. Each SVI must match with the VLAN number.
o Routing – Routing must be enabled. Each interface or network should be added to the routing protocol, or static routes entered, where appropriate.
o Hosts – Hosts must have the correct IP address or subnet mask. Hosts must have a default gateway associated with an SVI or routed port.
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2.4 Chapter Summary
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Chapter Summary 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.
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Chapter Summary Summary (Cont.)
§ 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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