[Day 9] 7. Inter-VLAN Connection

Inter-VLAN Routing (Router-on-a-Stick Configuration)

Explanation:

Inter-VLAN routing is necessary when devices in different VLANs need to communicate. This is achieved by using a router to route traffic between VLANs. A common method for implementing this is known as Router-on-a-Stick.

In a Router-on-a-Stick configuration, the router uses a single physical interface (such as FastEthernet 0/0) to handle traffic for multiple VLANs. To enable this, we create sub-interfaces on the router, each of which is associated with a specific VLAN.

• Each sub-interface acts as a virtual interface for a particular VLAN.
• Sub-interfaces allow the router to communicate with multiple VLANs through a single physical interface.
• The VLAN information is encapsulated (tagged) using 802.1Q or ISL.

Router Configuration Steps:

1. Create a sub-interface for the desired VLAN:

   bashCopy
   R1(config)# int fa0.2
   

2. Assign an IP address to the sub-interface (for the corresponding VLAN):

   bashCopy
   R1(config-if)# ip address 172.16.10.1 255.255.255.0
   

3. Configure encapsulation for the VLAN (using 802.1Q or ISL):

   • For 802.1Q:

     bashCopy
     R1(config-if)# encapsulation dot1q 2
     

   • For ISL:

     bashCopy
     R1(config-if)# encapsulation isl 2
     

Monitoring Commands:

1. Copy

   show vlan

   : Displays information about the VLANs configured on the switch.

2. Copy

   show vlan brief

   : Shows a concise summary of the VLANs on the switch.

3. Copy

   show int trunk

   : Displays trunk link status and VLANs allowed on trunk interfaces.

4. Copy

   show mac-address table

   : Lists the MAC addresses learned on each switch port.

5. Copy

   show vtp status

   : Displays the status of the VTP (VLAN Trunking Protocol) on the switch, including domain name and mode.