CCNA | VLANS CON. |

Native VLAN Feature on Routers

• Best Practice: Set the native VLAN to an unused VLAN due to security issues.

• VLAN Efficiency: Frames in the native VLAN aren't tagged, making the transfer of frames more efficient leading to higher frame rates.

• Demonstration Context: Previous configuration used VLAN 1001; changed to a used VLAN (VLAN 10) on trunks.

Configuring Native VLAN on a Router

Two Methods

1. Subinterface Configuration

   • Command: encapsulation dot1Q [VLAN ID] native

   • Function: Assigns the subinterface to the native VLAN, allowing untagged frames to be treated as part of that VLAN.

2. Physical Interface Configuration

   • No need for a subinterface or encapsulation dot1Q command. Just configure IP directly on the physical interface.

Wireshark Demonstration

• Traffic Analysis: Monitored ICMP echo request from VLAN 20 (PC with IP 192.168.1.65) to router, demonstrating VLAN tagging and native VLAN functioning.

• Tagged vs Untagged Frames:

  • Tagged Frame Example: Frame from VLAN 20 tagged; contains information under the 802.1Q header.

  • Untagged Frame Example: Frame from router to VLAN 10 untagged due to it being configured as the native VLAN, illustrating how native VLAN functions.

Multilayer Switch

Definition

• A multilayer switch (Layer 3 switch) performs both switching and routing tasks, aware of Layer 3 protocols.

• Capable of IP address assignments on interfaces, unlike traditional Layer 2 switches.

Key Features

• Routed Ports: Function like router interfaces, allowing for inter-VLAN routing.

• Switch Virtual Interfaces (SVIs):

  • Virtual interfaces with IP assignments used for routing traffic within VLANs.

  • Configuring SVIs eliminates the need for router assistance in routing between VLANs.

Inter VLAN Routing

• Traditional Router Method: Uses multiple connections for each VLAN or "router on a stick" for efficient use of router interfaces but can cause congestion.

• Multilayer Switch Routing: Directly connects PCs to VLANs; uses SVIs to route packets without involving a router, streamlining the process.

Key Configuration Steps

1. Point-to-Point Connection

   • Change interface configurations for both router and multilayer switch from trunking to routed connections.

2. Switch Configuration

   • Enable Layer 3 routing with the command IP routing.

   • Convert interfaces from switch ports to routed ports using no switchport.

3. SVI Configuration

   • Create SVIs using interface VLAN [VLAN ID], assign IP addresses, and enable with no shutdown command.

Conditions for SVI Status

• Requirements for SVI to be 'up':

  • The corresponding VLAN must exist on the switch.

  • At least one access port must be active in the VLAN.

  • The VLAN must be in a non-shutdown state, and SVIs cannot be shut down.

Summary of Key Learning Points

• Two ways of configuring native VLAN on routers.

• Importance of using unused VLANs for security.

• Introduction of multilayer switches for effective inter VLAN routing.

• Understanding SVIs and their configurations simplify routing tasks significantly.