Trouble Ticket 6 VLAN and Spanning-Tree Lab
Just as loops can occur in the upper layers because of mutual redistribution and improper filtering, they can also occur at Layer 2. Back in Chapters 6 and 7 I spent some time on the Spanning Tree Protocol (STP). STP assists with bridge/switch loops and it is normally not the best practice to just turn it off. As a matter of fact, Cisco performs a per-VLAN STP. VLANs help you segment your broadcast domains and use a lesser number of routers while doing so. However, the ideal design is still hierarchical in nature.
In this Trouble Ticket, you are just starting to implement VLANs and are thinking about upgrading your 1900 switch. For now, knappsnarrows and hostb are both in the default VLAN 1, which requires no configuration on the 1900 on your part except for management IP addressing.
To prepare for Trouble Ticket 6 you need to make a minor physical change to the topology by shutting down the e0/0 interface on the osprey router and port 12 on the knappsnarrows switch. Alternatively, just remove the cable between them. Two additional connections are required between kentnarrows and knappsnarrows as shown in Figure 10-9.
Start your testing from hosta to work toward any major issues. When you can successfully telnet to kentnarrows, chesapeakebay, and knappsnarrows from hosta, hostb, and hostc, that is definitely an accomplishment. You have finished the labs when you can console directly into the devices and copy the configurations to the TFTP server.
Trouble Ticket 6 VLAN and Spanning-Tree Lab Solution
Use the following list to make sure you found and fixed all the issues I planned. Obviously there may have been others, too.
General issues:
Physically you need two crossover cables between the two switches for redundancy.
Hosts tables.
Leftovers from previous Trouble Tickets.
goose (r3) issues:
Console speed set to 2400. Change your terminal program settings or telnet in to change it back to the 9600 default.
fa2/0 administratively shut down.
fa2/0 speed.
fa2/0 duplex.
kentnarrows (s2) issues:
fa0/12 is missing the switchport mode trunk statement for kentnarrows. Use the show interfaces fa0/12 switchport command to verify.
No default gateway.
VLAN1 address should be 172.16.1.42/29.
fa0/12 speed.
fa0/12 duplex.
No STP on VLAN1, so what will take care of the Layer 2 redundancy between kentnarrows and knappsnarrows? Turn it back on with the spanning-tree vlan 1 command.
Compare your final saved fixed configurations to the tt6 fixed configs file. Add any additional notes to your drawing and tables.
Now that you have completed these challenging Trouble Tickets, go back and review all your documentation. I highly recommend you print the supporting files for this chapter and “swim” through the Trouble Tickets once again. Practice makes perfect. Shooting internetworking troubles is not just something you can pick up a book on and expect to be successful. To alleviate your fears, you must put your theory to practical use.