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VLAN Communications: Making Networks Talk to Each Other

  • Date: Jul 7, 2015.

Contents

  1. Overview
  2. Communications Options
  3. The Forwarding Path
  4. Network Configuration
  5. Summary

Article Description

Sean Wilkins, co-author of CCNA Routing and Switching 200-120 Network Simulator, discusses routing and communications options for virtual networks in various configurations.

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Network Configuration

Configuring any of the network options requires a good understanding of the concepts laid out in the previous sections. All of the following examples use four different VLANs: VLAN 10, VLAN 20, VLAN 30, and VLAN 40.

The option 1 configuration requires the interfaces connected to the router to be configured into the correct VLANs. No special configuration is required on R1, as each interface would be configured like a standard LAN interface; the VLANs are invisible to R1 in this configuration.

Table 1 shows an example, using the diagram from Figure 1.

Table 1

Step

Action(s)

Command(s)

1

Enter global configuration mode.

SW1#configure terminal

2

Enter into VLAN configuration mode and/or create a VLAN (optional).

SW1(config)#vlan vlan-id

3

Configure a name for the VLAN (optional).

SW1(config-vlan)#name name

4

Enter into interface configuration mode for the first interface connecting to R1.

SW1(config-vlan)#interface fastethernet0/0

5

Configure the access VLAN for the interface.

SW1(config-if)#switchport access vlan 10

6

Enter into interface configuration mode for the second interface connecting to R1.

SW1(config-vlan)#interface fastethernet0/1

7

Configure the access VLAN for the interface.

SW1(config-if)#switchport access vlan 20

8

Enter into interface configuration mode for the third interface connecting to R1.

SW1(config-vlan)#interface fastethernet0/2

9

Configure the access VLAN for the interface.

SW1(config-if)#switchport access vlan 30

10

Enter into interface configuration mode for the fourth interface connecting to R1.

SW1(config-vlan)#interface fastethernet0/3

11

Configure the access VLAN for the interface.

SW1(config-if)#switchport access vlan 40

For option 2, the router must become aware of the VLANs being used and route accordingly. Table 2 shows an example of this configuration, using the diagram from Figure 2.

Table 2

Step

Action(s)

Command(s)

1

Enter global configuration mode.

SW1#configure terminal

2

Enter into VLAN configuration mode and/or create a VLAN (optional).

SW1(config)#vlan vlan-id

3

Configure a name for the VLAN (optional).

SW1(config-vlan)#name name

4

Enter into interface configuration mode for the first interface connecting to R1.

SW1(config-vlan)#interface fastethernet0/0

5

Configure the interface to become a trunk.

Note: Routers don’t support the dynamic trunking protocol (DTP), so the trunk must be manually enabled.

SW1(config-if)#switchport mode trunk

6

Enter global configuration mode.

R1#configure terminal

7

Create a new sub-interface on the physical interface connecting to SW1.

Note: For this example, I’m using sub-interface numbers that match the VLAN numbers, but this is not required.

R1(config)#interface fastethernet0/0.10

8

Configure the interface to use IEEE 802.1Q encapsulation and handle traffic for VLAN 10.

R1(config-if)#encapsulation dot1Q 10

9

Create another new sub-interface on the physical interface connecting to SW1.

R1(config)#interface fastethernet0/0.20

10

Configure the interface to use IEEE 802.1Q encapsulation and handle traffic for VLAN 20.

R1(config-if)#encapsulation dot1Q 20

11

Create another new sub-interface on the physical interface connecting to SW1.

R1(config)#interface fastethernet0/0.30

12

Configure the interface to use IEEE 802.1Q encapsulation and handle traffic for VLAN 30.

R1(config-if)#encapsulation dot1Q 30

8

Create another new sub-interface on the physical interface connecting to SW1.

R1(config)#interface fastethernet0/0.40

9

Configure the interface to use IEEE 802.1Q encapsulation and handle traffic for VLAN 40.

R1(config-if)#encapsulation dot1Q 40

All Layer 3 addressing information would now be configured on the sub-interfaces that are configured.

For option 3, the configuration requires that you set up the SVI within the switch to handle the VLAN traffic. Table 3 shows an example of this configuration, using the diagram from Figure 3.

Table 3

Step

Action(s)

Command(s)

1

Enter global configuration mode.

SW1#configure terminal

2

Enter into VLAN configuration mode and/or create a VLAN (optional).

SW1(config)#vlan vlan-id

3

Configure a name for the VLAN (optional).

SW1(config-vlan)#name name

4

Configure a new SVI interface for the first VLAN (10).

SW1(config-vlan)#interface vlan 10

5

Configure a new SVI interface for the second VLAN (20).

SW1(config-vlan)#interface vlan 20

6

Configure a new SVI interface for the third VLAN (30).

SW1(config-vlan)#interface vlan 30

7

Configure a new SVI interface for the fourth VLAN (40).

SW1(config-vlan)#interface vlan 40

All Layer 3 addressing information would now be configured on the SVI interfaces that are configured.

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