What Is Router on a Stick Inter-VLAN Routing?
Router on a stick interVLAN routing is a computer networking method used for managing traffic between different VLANs (Virtual Local Area Networks) on a single physical router interface.
This method is often employed in small or medium-sized networks where there is a need for inter-VLAN routing but not enough traffic to justify multiple physical interfaces for each VLAN.
Here’s a briefly how InterVLAN Routing works:
Single Physical Interface: The router uses a single interface to connect to a switch. This interface is configured as a trunk port to allow traffic from multiple VLANs.
Subinterfaces: The single physical interface on the router is divided into multiple logical interfaces, known as subinterfaces.
Each subinterface is associated with a different VLAN. This is similar to having multiple virtual routers within a single physical router.
When configuring InterVLAN routing, it’s advisable you first, configure the switch SW1 that will be connected to the router, as shown in the diagram.
Router R1 is connected to switch ports F0/4 and F0/3, which have been configured for VLANs 10 and 20, respectively.
Example of switch SW1 physical interface configuration command:
SW1#config t
SW1(config)#vlan 10
SW1(config-vlan)#vlan 20
SW1(config-vlan)#exit
SW1(config)#interface fa0/8
SW1(config-if)#switchport access vlan 10
SW1(config-if)#interface fa0/4
SW1(config-if)#switchport access vlan 10
SW1(config-if)#interface fa0/11
SW1(config-if)#switchport access vlan 20
SW1(config-if)#interface fa0/3
SW1(config-if)#switchport access vlan 20
SW1(config-if)#end
#SYS-5-CONFIG_I: configured from console by console
SWI#
In the above example, interfaces F0/4 and F0/8 have been configured on VLAN 10 using the switchport access vlan 10 command. The same process is used to assign VLAN 20 to interface F0/3 and F0/11 on switch SW1.
To be on the safe side use the copy running-config startup-config command in privileged EXEC mode to save your configuration
Example of router R1 interface configuration command:
R1#config t
R1(config)#interface fa0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shut
….
R1(config-if)#interface fa0/1
RI(config-if)#ip address 192.168.2.1 255.255.255.0
RI(config-if)#no shut
RI(config-if)#end
As shown in the figure above, each router interface – fa0/0 and fa0/1 – belongs to a different subnet and is configured with an IP address and subnet mask in the interface configuration mode, and no shutdown command is used to enable the router interface.
After the no shutdown is issued in interface configuration mode, you will notice a display indicating that the interface state has changed to up. This indicates that the interface is now enabled.
You can examine the routing table using the show ip route privileged EXEC mode command. This command displays the locally connected interfaces of the router.
You can also use the show interface command in privileged EXEC mode to view more detailed information about the router interfaces, such as diagnostic information, status, MAC address, and transmit or receive errors.
In summary:
If the router receives a packet on interface F0/0 destined for the 192.168.2.0 subnet, the router would identify that it should send the packet out via interface F0/1 to reach hosts on the 192.168.2.0 subnet.
InterVLAN Routing Sub-Interface
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