To demonstrate a simple Cisco router on a stick configuration, I utilize a Cisco c3725 configured as a switch, two linux hosts, and a Cisco c7200 router to act as the gateway between the networks. The host named 172Host has the IP address 172.16.1.2/24 and its connected switch port is on VLAN 1. VLAN 2 host the 192Host with IP address 192.168.0.2/24. The c7200 has two subinterfaces on fa0/0: FastEthernet 0/0.1 with IP address 172.16.0.1/24 and FastEthernet 0/0.2 with IP address 192.168.0.1/24. The FastEthernet 0/0 interface is connected to the FastEthernet 1/2 port on the switch and this port is configured for trunking (using 802.1q encapsulation).
172Host and 192Host are Linux systems, the important pieces of the configuration are shown below (this can be verified using the ifconfig -a and the route command). This includes setting the IP address and default gateway.
root@192Host:~# ifconfig eth0 192.168.0.2 mask 255.255.255.0 root@192Host:~# route add default gw 192.168.0.1 eth0 root@172Host:~# ifconfig eth0 172.16.0.2 mask 255.255.255.0 root@172Host:~# route add default gw 172.16.0.1 eth0
The important pieces of the configuration on R1 and S1 are shown below,
! On S1 !
! interface FastEthernet1/0 ! interface FastEthernet1/1 switchport access vlan 2 ! interface FastEthernet1/2 switchport mode trunk !
!!!!!!!!!!!!! ! On R1 !
interface FastEthernet0/0 no ip address duplex auto speed auto ! interface FastEthernet0/0.1 encapsulation dot1Q 1 native ip address 172.16.0.1 255.255.255.0 ! interface FastEthernet0/0.2 encapsulation dot1Q 2 ip address 192.168.0.1 255.255.255.0 !
After the configuration is complete, a full inter-VLAN routing solution is complete and 172Host and 192Host can successfully ping each other.
root@172Host:~# ping -c 4 192.168.0.2 PING 192.168.0.2 (192.168.0.2): 56 data bytes 64 bytes from 192.168.0.2: seq=0 ttl=63 time=18.025 ms 64 bytes from 192.168.0.2: seq=1 ttl=63 time=24.678 ms 64 bytes from 192.168.0.2: seq=2 ttl=63 time=21.445 ms 64 bytes from 192.168.0.2: seq=3 ttl=63 time=17.711 ms --- 192.168.0.2 ping statistics --- 4 packets transmitted, 4 packets received, 0% packet loss round-trip min/avg/max = 17.711/20.464/24.678 ms root@192Host:~# ping -c 4 172.16.0.2 PING 172.16.0.2 (172.16.0.2): 56 data bytes 64 bytes from 172.16.0.2: seq=0 ttl=63 time=17.665 ms 64 bytes from 172.16.0.2: seq=1 ttl=63 time=14.784 ms 64 bytes from 172.16.0.2: seq=2 ttl=63 time=22.809 ms 64 bytes from 172.16.0.2: seq=3 ttl=63 time=18.777 ms --- 172.16.0.2 ping statistics --- 4 packets transmitted, 4 packets received, 0% packet loss round-trip min/avg/max = 14.784/18.508/22.809 ms
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