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
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.