How to Configure Inter-VLAN Routing With ROAS _ TechVine Tech Support Blog

7/24/2014 How to configure Inter-VLAN Routing with ROAS | TechVine Tech Support Blog

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How to configure Inter-VLAN Routing with ROAS

October 24, 2013

Cisco

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In this post we are going to show you how you can implement router on a stick. You can use cisco packet tracer

program as a virtual lab on your computer. Figure 1 shows the scenario that we are going to implement.

What is a Router on a stick?

A Stub router, One-armed router or router on a stick, is a router that routes traffic between virtual local area

networks (VLANs). It has only a single Ethernet NIC that is part of two or more Virtual LANs, enabling them to be

joined.

A switch allows multiple virtual LANs to coexist on the same physical switch. This means that two machines

attached to the same switch cannot send Ethernet frames to each other. If they need to communicate, then a

router must be placed between the two VLANs to forward packets between them, just as if the two LANs were

physically isolated. The only difference is that the router contains only a single Ethernet NIC that is part of both

VLANs. Hence we call it Router on a stick or one-armed.

Figure 1

First we are going to add a Cisco 2960 switch and 2 computers to our virtual lab and then we configure 2 VLANs

on the switch that are named VLAN 10 (Accounting) and VLAN 20 (Engineering) as depicted in Figure 1.

Step 1

To configure the VLANs on the switch follow these steps:

1. Switch#config t

2. Switch(config)#vlan 10

3. Switch(config-vlan)#Name Accounting

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4. Switch (config-vlan)#exit

5. Switch(config)#vlan 20

6. Switch(config-vlan)#Name Engineering

7. Switch (config-vlan)#exit

With the above commands you have successfully configured the VLAN 10 and VLAN 20 on the switch and you

have assigned names to them.

Now we are going to assign Fa0/1 port to Accounting (VLAN 10) and Fa0/2 port to Engineering (VLAN 20) that we

made in Step 1.

Step 2

To assign the ports to the VLANs follow these steps:

1. Switch(config)#interface fastEthernet 0/1

2. Switch(config-if)#switchport mode access

3. Switch(config-if)#switchport access vlan 10

4. Switch(config-if)#exit


6. Switch(config-if)#switchport mode access

7. Switch(config-if)#switchport access vlan 20

Verify the result of Step 1 and Step 2 by typing the Show vlan brief command on the switch.

Figure 2

Now lets add a 2621 router and configure it to route the packets between 2 VLANs.

Step 3

Configure 2 virtual interfaces on fa0/1 and assign them to VLAN 10 and VLAN 20 for the sake of making

configuration understandable to everyone it is better to use the same names or numbers for the VLANs (Here we

use VLAN 10 and VLAN 20 as we used them before in our switch configuration).

1. Router(config)#interface fastEthernet 0/0.10

2. Router(config-subif)#encapsulation dot1Q 10

3. Router(config-subif)#ip address 192.168.10.1 255.255.255.0

4. Router(config-subif)#exit

5. Router(config)#interface fastEthernet 0/0.20

6. Router(config-subif)#encapsulation dot1Q 20

7. Router(config-subif)#ip address 192.168.20.1 255.255.255.0



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8. Router(config-subif)#exit

9. Router(config)#interface fastEthernet 0/0

10. Router(config-if)#no shutdown

On the switch we need to make the port that connects our switch to the router a trunk port to make it work. In our

demonstration we are using port Fa0/24 as a trunk port. Follow below steps to make port 24 a trunk port.

Step 4


2. Switch(config-if)#switchport trunk allowed vlan 10,20

3. Switch(config-if)#switchport mode trunk

With these 4 steps you have configured the router to route the traffic between the VLANs. You can add 2

computers to the ports that you have configured and assign them IP address to test the result. Just pay attention

that the default gateway address of each computer in each VLAN is the routers virtual interface IP address that

you have configured for the same VLAN.

Figure 3

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How to Configure Inter-VLAN Routing With ROAS _ TechVine Tech Support Blog

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