Lab 3.2.3 Building a Switched Network with Redundant Links

Step 1: Cable the network

a. Connect Host 1 to Switch 1 Fast Ethernet port Fa0/7, using a straight-through Ethernet cable.

b. Connect Host 2 to Switch 2 Fast Ethernet port Fa0/8, using a straight-through Ethernet cable.

c. Connect Switch 1 Fast Ethernet port Fa0/1 to Switch 2 Fast Ethernet port Fa0/1, using a crossover Ethernet cable.

d. Create a redundant link between the switches by connecting Switch 1 Fast Ethernet port Fa0/4 to Switch 2 Fast Ethernet port Fa0/4, using a crossover Ethernet cable. What typically undesirable traffic pattern have you created by using the two crossover cables between the two switches?

Predict: What do you think the switches will do to keep this from becoming a problem?

Step 2: Configure the switches

Step 3: Configure the hosts

a. Configure each host to use an IP address in the same network as the switches.

b. Configure each host to use the same subnet mask as the switches. Why is no default gateway specified for this network?

Step 4: Verify connectivity

a. To verify that the network is set up successfully, ping from Host 1 to Host 2. Was the ping successful?

b. If the ping is not successful, verify the connections and configurations again. Check to ensure that all cables are correct and that connections are seated. If the ping is not successful, what utility could you use to determine where the connection is failing?

Step 5: Examine interface VLAN 1 information

a. From the terminal emulation session on either switch, enter the command show interface vlan1 ? at the privileged EXEC mode prompt.

SwitchA#show interface vlan1 ?

List some of the options that are available

b. On SwitchA, enter the command show interface vlan1 at the privileged EXEC mode prompt. SwitchA#show interface vlan1

What is the MAC address of the switch?

What other term for MAC address is used?

c. On SwitchB, enter the command show interface vlan1 at the privileged EXEC mode prompt. What is the MAC address of the switch?

Which switch should be the root of the spanning tree for this network?

Step 6: Examine the spanning-tree tables on each switch

a. On SwitchA, enter the command show spanning-tree at the privileged EXEC mode prompt.

b. On SwitchB, enter the command show spanning-tree at the privileged EXEC mode prompt.

c.  Examine the outputs and answer the following questions:

Which switch is the root bridge?

What is the priority of the root bridge?

What is the bridge ID of the root bridge?

Which ports are forwarding on the root bridge?

Which ports are blocking on the root bridge?

What is the priority of the non-root bridge?

What is the bridge ID of the non-root bridge?

Which ports are forwarding on the non-root bridge?

Which ports are blocking on the non-root bridge?

d. Examine the link lights on both switches.

Can you tell which port is in blocking state?

Why is there no change in the link lights?

Step 7: Reassign the root bridge

What would you do if you wanted a different switch to be the root bridge for this network?

Why might you want to do this?

For the purposes of this lab, assume that the switch that is currently the root bridge is undesirable. The example assumes that SwitchB is preferred as the root switch. To “force” SwitchB to become the new root bridge, you need to configure a new priority for it.

a. Go to the console and enter configuration mode on SwitchB.

b. Determine the options that can be configured for the Spanning Tree Protocol by issuing this command: SwitchB(config)#spanning-tree ?

c. List the options that are available: _____________________

d. Set the priority of the switch to 4096.

SwitchB(config)#spanning-tree vlan 1 priority 4096

SwitchB(config)#exit

Step 8: Look at the spanning-tree table

a. On SwitchA, enter show spanning-tree at the privileged EXEC mode prompt.

b. On SwitchB, enter show spanning-tree at the privileged EXEC mode prompt.

c. Examine the outputs and answer the following questions:

Which switch is the root bridge?

What is the priority of the root bridge?

What is the bridge ID of the root bridge?

Which ports are forwarding on the root bridge?

Which ports are blocking on the root bridge?

What is the priority of the non-root bridge?

What is the bridge ID of the non-root bridge?

Which ports are forwarding on the non-root bridge?

Which ports are blocking on the non-root bridge?

Step 9: Verify the running configuration file on the root bridge

a. On the switch that was changed to be the root bridge, enter the show running-configcommand at the privileged EXEC mode prompt.

b. Locate the spanning-tree priority information for this switch.

c. How can you tell from the information given that this switch is the root bridge?

Step 10: Reflection

Suppose that you are adding new switches to a company’s network. Why should you plan the physical design carefully? Why should you be prepared to make adjustments to factory default settings?