In Cisco switches, VLAN 1 refers to the default VLAN that is created automatically when the switch is initialized or reset to factory settings. It is the default VLAN for user traffic and is typically associated with the native VLAN on trunk ports.
VLAN 1 serves multiple purposes in Cisco switches:
1. Default VLAN: VLAN 1 is the default VLAN assigned to all switch ports unless explicitly configured otherwise. When a switch port is not assigned to a specific VLAN, it belongs to VLAN 1 by default.
2. Management Traffic: VLAN 1 is commonly used for management purposes, including switch management protocols, such as Telnet, SSH, SNMP, and Simple Network Management Protocol (SNMP) traps. It is the default VLAN for accessing the switch’s management interface.
3. Control Plane Traffic: VLAN 1 is also used for control plane traffic, which includes protocols like CDP (Cisco Discovery Protocol) and STP (Spanning Tree Protocol). These protocols help manage and maintain the network’s stability and topology.
However, it is important to note that while VLAN 1 is commonly used as the default VLAN, it does not possess any inherent magical properties or superiority over other VLANs. In fact, for security reasons, it is generally recommended to avoid using VLAN 1 for user traffic and to change the default VLAN to a different VLAN ID. This practice helps improve network security by reducing the potential risks associated with attacks targeting the default VLAN.
WHY AVOID USING VLAN 1
In Cisco networks, it is generally considered a security best practice to change from using VLAN 1 as the default VLAN for user traffic. While VLAN 1 is commonly used as the default VLAN in Cisco switches, it is not inherently “magical” or more powerful than other VLANs. The primary reason for changing from VLAN 1 is to enhance network security and reduce potential risks.
Here are a few reasons why it is recommended to avoid using VLAN 1 for user traffic:
1. Security concerns: VLAN 1 is often targeted by attackers because it is commonly known as the default VLAN. If an attacker gains access to VLAN 1, they may have an easier time moving laterally across the network.
2. VLAN hopping attacks: VLAN hopping is a technique used to bypass security measures by exploiting vulnerabilities in VLAN trunking protocols. Changing the default VLAN reduces the risk of such attacks by making it harder for an attacker to gain unauthorized access to VLANs.
3. Misconfiguration risks: Using VLAN 1 for user traffic increases the chances of accidental misconfiguration. Since VLAN 1 is typically used for management purposes, there is a higher likelihood of configuration errors that can impact network functionality.
4. Segmentation and organization: By using a different VLAN for user traffic, network administrators can better organize and segment their network. This enables more granular control over access policies, facilitates troubleshooting, and enhances overall network management.
Changing from VLAN 1 to another VLAN is a recommended practice to improve network security and reduce potential risks associated with using the default VLAN. It is important to implement proper security measures, such as strong access controls and VLAN segmentation, regardless of the VLAN being used.
CONTROL PLANE AND DATA PLAN
VLANs are utilized in both the control plane and data plane of a network. Let’s explore their roles in each plane:
1. Control Plane: The control plane is responsible for managing the network’s infrastructure, including routing protocols, management traffic, and other control functions. VLANs play a crucial role in organizing and segregating control plane traffic. For example, Cisco devices use VLAN 1 as the default VLAN for control plane traffic, including management protocols like Cisco Discovery Protocol (CDP) and Spanning Tree Protocol (STP).
2. Data Plane: The data plane, also known as the forwarding plane, handles the actual forwarding of user data across the network. VLANs are used to logically separate and isolate traffic belonging to different network segments or groups. By assigning different VLANs to different ports or interfaces, traffic can be kept separate and only reach its intended destination.
REMOVE NATIVE VLAN 1 FROM TRUNK PORT
Now, let’s discuss the scenario of changing the native VLAN and removing VLAN 1 from a trunk:
When the native VLAN is changed on a trunk link, it affects the untagged traffic that flows through that link. The native VLAN is used for traffic that does not have a VLAN tag attached, and it is typically used for carrying management traffic or for communication with devices that do not support VLAN tagging. Changing the native VLAN can impact the handling of untagged traffic on the trunk link and requires ensuring that all connected devices are properly configured to handle the new native VLAN.
If VLAN 1 is removed from a trunk link, it can have several effects:
1. Control Plane Traffic: As mentioned earlier, VLAN 1 is often used as the default VLAN for control plane traffic. Removing VLAN 1 from the trunk may disrupt the management and control functions that rely on this VLAN. It is important to ensure that the necessary control plane traffic is redirected to an appropriate VLAN if VLAN 1 is removed.
2. Native VLAN Traffic: If VLAN 1 is the native VLAN on the trunk, removing it may affect the handling of untagged traffic on the link. The new native VLAN should be configured correctly on both ends of the trunk to ensure proper communication.
3. Network Segmentation: VLAN 1 is often used for user data as well. Removing VLAN 1 from the trunk means that devices assigned to VLAN 1 will no longer be able to communicate across that trunk link. Network segmentation may need to be reconfigured or other VLANs should be used to maintain the desired traffic separation.
In summary, changing the native VLAN and removing VLAN 1 from a trunk link can impact the handling of control plane traffic, untagged traffic, and network segmentation. It requires careful planning, configuration updates on both ends of the trunk, and consideration of the impact on different types of traffic and VLAN assignments.
CONFIGURATION EXAMPLE
In Cisco switches, it is not possible to completely disable or remove VLAN 1 since it is a mandatory VLAN. However, you can effectively disable VLAN 1 by removing all switch ports from VLAN 1 and assigning them to a different VLAN. This prevents any user traffic from being associated with VLAN 1.
Here’s an example of disabling VLAN 1 by removing switch ports from it and assigning them to VLAN 222 as the native VLAN:
1. VLAN Configuration:
Create VLAN 222 and assign it as the native VLAN:
switch# configure terminal
switch(config)# vlan 222
switch(config-vlan)# name Native VLAN
switch(config)# interface range GigabitEthernet 1/0/1-24 (example range of interfaces)
switch(config-if-range)# switchport access vlan 222
2. Trunk Port Configuration:
Configure the trunk port and tag VLANs 10, 20, and 30:
switch(config)# interface GigabitEthernet 1/0/1 (example interface)
switch(config-if)# switchport mode trunk
switch(config-if)# switchport trunk allowed vlan 10,20,30
switch(config-if)# switchport trunk native vlan 222
In this example, VLAN 222 is created and named “Native VLAN.” The switch ports are removed from VLAN 1 and assigned to VLAN 222 using the “switchport access vlan” command. The trunk port is configured to tag VLANs 10, 20, and 30, with VLAN 222 designated as the native VLAN.
Remember to adjust the interface range (e.g., GigabitEthernet 1/0/1-24) and VLAN IDs to match your specific network configuration. By removing switch ports from VLAN 1 and assigning them to a different VLAN, you effectively disable VLAN 1 for user traffic.