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.

SW0 Commands

enable

vlan database 
vlan 10
vlan 20
apply 
exit

conf t
hostname SW0

int f0/0
switchport mode trunk
switchport trunk encapsulation dot1q

int f0/1
switchport mode access
switchport access vlan 10

int f0/2
switchport mode access
switchport access vlan 20

exit
exit
write

R0 Commands

enable

vlan database 
vlan 10
vlan 20
apply 
exit

conf t
hostname R0

int f0/0
no shutdown

int f0/0.10
encapsulation dot1Q 10
ip ad 192.168.10.1 255.255.255.0

int f0/0.20
encapsulation dot1Q 20
ip ad 192.168.20.1 255.255.255.0

exit
exit
write

PC1 Commands

enable

conf t
hostname PC1

int f0/0
no shutdown
ip ad 192.168.10.2 255.255.255.0
exit

ip route 0.0.0.0 0.0.0.0 192.168.10.1

exit
write

PC2 Commands

enable

conf t
hostname PC2

int f0/0
no shutdown
ip ad 192.168.20.2 255.255.255.0
exit

ip route 0.0.0.0 0.0.0.0 192.168.20.1

exit
write

PC1 Test

PC1#ping 192.168.10.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.10.1, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 4/9/16 ms
PC1#ping 192.168.20.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.20.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/10/16 ms

PC2 Test

PC2#ping 192.168.20.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.20.1, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 4/5/8 ms
PC2#ping 192.168.10.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.10.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms

SW0 Config

!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname SW0
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
!
!
ip cef
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
 switchport mode trunk
!
interface FastEthernet0/1
 switchport access vlan 10
!
interface FastEthernet0/2
 switchport access vlan 20
!
interface FastEthernet0/3
!
interface FastEthernet0/4
!
interface FastEthernet0/5
!
interface FastEthernet0/6
!
interface FastEthernet0/7
!
interface FastEthernet0/8
!
interface FastEthernet0/9
!
interface FastEthernet0/10
!
interface FastEthernet0/11
!
interface FastEthernet0/12
!
interface FastEthernet0/13
!
interface FastEthernet0/14
!
interface FastEthernet0/15
!
interface Vlan1
 no ip address
!
ip http server
!
ip forward-protocol nd
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
!
!
line con 0
line aux 0
line vty 0 4
!
!
end

R0 config

!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R0
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
!
!
ip cef
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
!
interface FastEthernet0/0.10
 encapsulation dot1Q 10
 ip address 192.168.10.1 255.255.255.0
!
interface FastEthernet0/0.20
 encapsulation dot1Q 20
 ip address 192.168.20.1 255.255.255.0
!
ip http server
!
ip forward-protocol nd
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
!
!
line con 0
line aux 0
line vty 0 4
!
!
end

PC1 config

!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname PC1
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
!
!
ip cef
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
 ip address 192.168.10.2 255.255.255.0
 duplex auto
 speed auto
!
ip http server
!
ip forward-protocol nd
ip route 0.0.0.0 0.0.0.0 192.168.10.1
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
!
!
line con 0
line aux 0
line vty 0 4
!
!
end

PC2 Config

!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname PC2
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
!
!
ip cef
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
 ip address 192.168.20.2 255.255.255.0
 duplex auto
 speed auto
!
ip http server
!
ip forward-protocol nd
ip route 0.0.0.0 0.0.0.0 192.168.20.1
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
!
!
line con 0
line aux 0
line vty 0 4
!
!
end