Exercice 4.2.7 : Configure Router-on-a-Stick Inter-VLAN Routing

Part 1: Add VLANs to a Switch

Step 1: Create VLANs on S1

• Command to create VLAN 10 and VLAN 30:

  S1(config)# vlan 10
  S1(config)# vlan 30

Step 2: Assign VLANs to Ports

• Assign VLAN 10 to the port connected to PC1 (F0/11):

  S1(config)# interface f0/11
  S1(config-if)# switchport mode access
  S1(config-if)# switchport access vlan 10

• Assign VLAN 30 to the port connected to PC3 (F0/6):

  S1(config)# interface f0/6
  S1(config-if)# switchport mode access
  S1(config-if)# switchport access vlan 30

• Verify configuration using show vlan brief:

  S1# show vlan brief

  Output:

  VLAN Name                             Status    Ports
  ---- -------------------------------- --------- -------------------------------
  1    default                          active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
                                                  Fa0/5, Fa0/7, Fa0/8, Fa0/9
                                                  Fa0/10, Fa0/12, Fa0/13, Fa0/14
                                                  Fa0/15, Fa0/16, Fa0/17, Fa0/18
                                                  Fa0/19, Fa0/20, Fa0/21, Fa0/22
                                                  Fa0/23, Fa0/24, Gig0/1, Gig0/2
  10   VLAN0010                         active    Fa0/11
  30   VLAN0030                         active    Fa0/6
  1002 fddi-default                     active    
  1003 token-ring-default               active    
  1004 fddinet-default                  active    
  1005 trnet-default                    active   

Step 3: Test Connectivity Between PC1 and PC3

• Command to test:

  PC1> ping 172.17.30.10

Question: Were the pings successful? Why did you get this result? Answer: The pings did not work because the computers are in different IP networks.

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Part 2: Configure Subinterfaces

Step 1: Configure Subinterfaces on R1

• Configure G0/0.10 for VLAN 10:

  R1(config)# interface g0/0.10
  R1(config-subif)# encapsulation dot1Q 10
  R1(config-subif)# ip address 172.17.10.1 255.255.255.0

• Configure G0/0.30 for VLAN 30:

  R1(config)# interface g0/0.30
  R1(config-subif)# encapsulation dot1Q 30
  R1(config-subif)# ip address 172.17.30.1 255.255.255.0

Step 2: Verify Configuration

• Use show ip interface brief to verify:

  R1# show ip interface brief

Output: Both subinterfaces are initially down because the physical interface (G0/0) is disabled.

• Enable G0/0 to activate subinterfaces:

  R1(config)# interface g0/0
  R1(config-if)# no shutdown

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Part 3: Test Connectivity with Inter-VLAN Routing

Step 1: Ping Between PC1 and PC3

Question: The pings should still fail. Why? Answer: The switch has no trunk port connected to the router yet.

Step 2: Enable Trunking on S1

• Configure trunking on G0/1:

  S1(config)# interface g0/1
  S1(config-if)# switchport mode trunk

Question: How can you determine that the interface is a trunk port using the show vlan command? Answer: The interface is not listed in the Ports section when using:show vlan

• Use show interface trunk to verify:

  S1# show interface trunk

Output:

Port        Mode         Encapsulation  Status        Native vlan
Gig0/1      on           802.1q         trunking      1

Port        Vlans allowed on trunk
Gig0/1      1-1005

Port        Vlans allowed and active in management domain
Gig0/1      1,10,30

Port        Vlans in spanning tree forwarding state and not pruned
Gig0/1      1,10,30

Step 3: Test Connectivity

Question: What addresses do PC1 and PC3 use as their default gateway addresses? Answer: They use the subinterface's address.