Monitoring A Vlan: Stopping Cisco Switch Surveillance

Virtual Local Area Networks (VLANs) are used in computer networks to divide a physical network into multiple logical networks, enhancing security, flexibility, and scalability. This article will walk you through the steps of adding and removing VLANs from a Cisco switch. To stop monitoring a VLAN on a Cisco switch, you can either disable the entire SPAN session or remove specific source VLANs. Additionally, you can delete the VLAN database (vlan.dat) on a Cisco switch to erase all VLAN configurations.

Stopping a VLAN monitoring session on a Cisco switch does not require disabling the entire session

When it comes to VLAN monitoring on a Cisco switch, you might assume that disabling the entire session is the only way to stop it. However, that's not always necessary. You can make adjustments without bringing the whole session down.

For instance, if you want to add or remove a monitored VLAN, you don't need to stop the entire session. By default, the session is created in the shut state, so you can simply make adjustments without interrupting the overall monitoring process.

Here's an example of the command you would use to disable a specific VLAN within the session:

> switch(config-monitor)# no source vlan 3, 6-10 tx

This command tells the switch to stop monitoring VLAN 3 and VLANs 6 to 10. You can replace the VLAN numbers with the ones relevant to your network setup.

On the other hand, if you want to disable the entire VLAN monitoring session, including all the monitored VLANs, you would use this command:

> Switch(config-monitor)# shut

This command will bring down the entire SPAN session, disabling monitoring for all the configured VLANs.

In summary, while you can certainly disable the entire VLAN monitoring session on a Cisco switch if needed, it's not necessary if you just want to stop monitoring specific VLANs. The commands provided offer a more targeted approach to managing your VLAN monitoring without disrupting the rest of the session.

To add or remove monitored VLANs, use the 'switch(config-monitor)# no source vlan' command

To add or remove monitored VLANs, use the command:

Switch(config-monitor)# no source vlan

This command is used to remove a source VLAN from a monitoring session on a Cisco switch. The full command syntax is as follows:

Switch(config-monitor)# no source vlan vlan-id

Here, `vlan-id` is the ID of the VLAN that you want to remove from the monitoring session. For example, to remove VLAN 10 from the monitoring session, the command would be:

Switch(config-monitor)# no source vlan 10

This command is useful when you want to stop monitoring a specific VLAN on your Cisco switch. By removing the VLAN as a source, you will no longer receive mirrored traffic from that particular VLAN to your monitoring destination.

It's important to note that this command only removes the specified VLAN from the monitoring session. If you want to completely remove the monitoring session, you need to use the following command:

Switch(config-monitor)# no monitor session session_number

This command will delete the entire monitoring session, including all the source and destination configurations associated with it.

Additionally, if you want to add a VLAN as a source to a monitoring session, you can use the following command:

Switch(config-monitor)# source vlan vlan-id

This command will allow you to specify a VLAN as a source for the monitoring session, so you can receive mirrored traffic from that VLAN to your monitoring destination.

'-command'>VLANs can be deleted from a Cisco switch using the 'switch(config)# no vlan ' command

VLANs can be deleted from a Cisco switch using the switch(config)# no vlan command. This is a straightforward process, but it requires careful execution to ensure the desired results.

To begin, open the Command Line Interface (CLI) of the Cisco Catalyst Switch. This can be done using a console cable or remotely via Telnet or SSH. Once you've accessed the CLI, enter privileged EXEC mode by running the necessary command and providing the required password.

From here, navigate to the Global Configuration Mode by typing the following command:

Switch# configure terminal

Now, you can proceed to delete the VLAN by using the following command:

Switch(config)# no vlan

Remember to replace with the specific VLAN number you want to remove. For instance, if you intend to delete VLAN 10, the command would be:

Switch(config)# no vlan 10

Executing this command will effectively remove the specified VLAN from the Cisco switch.

It is worth noting that simply deleting the VLAN configuration may not be sufficient to completely erase all VLAN-related information from the switch. In some cases, the VLAN information is stored in a file called "vlan.dat" located in the flash storage of the switch. To check for this file, you can use the "show flash" command. If the file exists, you can delete it using the following command:

Switch# delete vlan.dat

By following these steps, you can successfully delete VLANs from a Cisco switch, ensuring that any associated configurations and data are also removed.

The VLAN database (vlan.dat) can be deleted from a Cisco switch using the 'delete vlan.dat' command

To stop monitoring a VLAN on a Cisco switch, you can use the following steps:

• Delete the switch configuration: This can be done by deleting the "startup-configuration" and then rebooting the switch. This will erase the switch's startup configuration.
• Delete the VLANs: Even after deleting the switch configuration, the VLANs may still be present. To completely erase all VLANs on the switch, you need to delete the "vlan.dat" file, which stores the VLAN information. This can be done by executing the command "delete vlan.dat" and then reloading the switch.

The VLAN database (vlan.dat) can be deleted from a Cisco switch using the "delete vlan.dat" command. This command is used to erase all VLANs configured on the switch. Here are the detailed steps to delete the VLAN database:

• Access the Cisco Switch's Command Line Interface (CLI): This can be done using a console cable or remotely using Telnet or SSH.
• Enter Privileged EXEC Mode: Once you've accessed the CLI, enter privileged EXEC mode by entering the necessary password.
• Enter Global Configuration Mode: Type the following command to enter global configuration mode: "switch# configure terminal".
• Delete the VLAN Database: Use the "delete vlan.dat" command to delete the VLAN database. For example: "Switch#delete vlan.dat". Confirm the deletion by pressing Enter.
• Reload the Switch: After executing the "delete vlan.dat" command, reload the switch for the changes to take effect.

It is important to note that deleting the VLAN database will remove all VLAN configurations from the Cisco switch. Make sure to back up any necessary configurations before proceeding. Additionally, ensure that you have the appropriate permissions and access rights to perform these operations.

To prevent VLAN bridging on a Cisco switch, enable spanning-tree portfast and bpduguard

Overview

Virtual Local Area Networks (VLANs) are used in computer networks to divide a physical network into multiple logical networks, enhancing security, flexibility, and scalability. VLAN bridging occurs when a switch connects two or more VLANs together, allowing communication between devices on different VLANs. This can be intentional or accidental, and it can have both positive and negative effects on network performance and security.

Spanning-Tree Portfast

Spanning-tree portfast is a feature on Cisco switches that allows you to immediately bring an interface configured as an access or trunk port to the forwarding state, bypassing the listening and learning states. This feature is useful when connecting a single workstation or server to the switch, as it allows the device to connect to the network immediately without waiting for the spanning tree to converge. However, it is important to note that enabling spanning-tree portfast on an interface connecting to another switch can create a spanning-tree loop, which can cause broadcast storms and address-learning problems. Therefore, it is crucial to use this feature only on ports connected to end stations.

BPDU Guard

Bridge Protocol Data Units (BPDUs) are messages sent between switches in a network to achieve the Spanning Tree Protocol (STP), which helps prevent bridging loops. BPDUs contain information about the switch port attributes, such as the MAC address, priority, and cost. BPDU guard is a security feature that can be enabled globally on the switch or per port. It is designed to protect the Layer 2 STP topology by blocking ports that receive BPDUs from connected devices. This feature is useful in preventing unauthorized devices from connecting to the network and disrupting the STP. When BPDU guard is enabled, if a BPDU is received on a port, the port is automatically disabled, and manual intervention is required to re-enable it. This provides a secure response to invalid configurations and helps maintain the integrity of the STP.

Preventing VLAN Bridging

To prevent VLAN bridging on a Cisco switch, you can enable both spanning-tree portfast and bpduguard. Spanning-tree portfast ensures that the ports connected to end devices are immediately forwarded, while BPDU guard protects against unauthorized connections or misconfigurations that could lead to bridging loops. By enabling both features, you can allow devices to connect to the network quickly while maintaining security and preventing unintended VLAN bridging.

Configuration Guidelines

When configuring spanning-tree portfast and bpduguard, it is important to follow these guidelines:

• Use spanning-tree portfast only on ports connected to end stations, such as workstations or servers. Do not enable it on ports connecting to another switch to avoid potential bridging loops.
• Globally enable BPDU guard on Port Fast-enabled ports using the command "spanning-tree portfast bpduguard default". This will shut down any Port Fast-enabled port that receives a BPDU.
• Alternatively, you can enable BPDU guard on a specific interface using the command "spanning-tree bpduguard enable". This will put the interface into an error-disabled state if it receives a BPDU.
• Always verify your configurations using the appropriate "show" commands and save your changes to the configuration file.

Frequently asked questions