So we've got connectivity! Now let's see if we still have that connectivity when the ports are placed into different VLANs. Cisco CCNA theory states that devices in different VLANs can't communicate without the intervention of a Layer 3 device, but let's see if that's true by placing R2 into VLAN 23. (VTP is already running on these switches.)
SW1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
SW1(config)#int fast 0/2
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 23
SW1(config-if)#^Z
Now that R2 and R3 are in separate VLANs, can they still send pings back and forth?
R2#ping 172.23.23.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.23.23.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R3#ping 172.23.23.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.23.23.2, timeout is 2 seconds:
.....
No, they can’t. The difference is that they’re now in separate VLANs, and devices in different VLANs can’t communicate unless routing is taking place somewhere. Here, no routing is taking place, so the pings don’t go through.
Put R3’s switch port into VLAN 23, and try the ping again.
SW2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
SW2(config)#interface fast0/3
SW2(config-if)#switchport mode access
SW2(config-if)#switchport access vlan 23
SW2(config-if)#^Z
SW2#show vlan brief
R3#ping 172.23.23.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.23.23.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
R2#ping 172.23.23.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.23.23.3, timeout is 2 seconds:
!!!!!
Now that R2 and R3 are in the same VLAN, pings can go through. This just proves the theory - that inter-VLAN communicate requires a Layer 3 device. Layer 3 switches are becoming more and more popular, but router-on-a-stick is still around - and we'll see how to configure that in our next tutorial!
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