CDP: Building Topology Diagram

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Cisco Discovery Protocol Lab

Lab pre-requisites:

Before we use official Cisco Labs let's practice a little more. You need to learn our topology and there is no better way of doing this but practically.

In our previous lab all switches and routers were assigned unique names. That is always a good strategy. Now we're going to build on that configuration and create a proper topology diagram utilizing Cisco proprietary layer 2 protocol called CDP.

Using SW1 ensure that CDP is enabled on the device.
Check if all interfaces are running CDP protocol.
Enable all interfaces on all routers (switches have all interfaces enabled by default).
Using CDP protocol draw a topology diagram to learn which interfaces are connected between devices.
On all switches and routers shutdown the interfaces that are not currently used.

SOLUTION

Let's have some fun solving the lab.

Using SW1 ensure that CDP is enabled on the device.

If you use 'show running-config' command you're not going to see anything related to CDP protocol as defaults never show in the running configuration. The solution is to use the following command:

SW1#show cdp

and here's the output:
Check if all interfaces are running CDP protocol.

Here, the bitmap shows only two interfaces. You should see that all interfaces (both switch and router) run CDP by default.
Enable all interfaces on all routers (switches have all interfaces enabled by default).
Click Branch router icon, and click CLI tab at the top. First, we must find out what interfaces are available. A quick way of verifying that is to use show ip int brief:

Notice!
Packet Tracer has a clock rate enabled on serial interface enabled by default.

Branch#show controllers serial0/0/0
Interface Serial0/0/0
Hardware is PowerQUICC MPC860
DTE V.35 TX and RX clocks detected

Now, you're ready to complete the task. Start with router Branch:

Branch#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Branch(config)#int fa0/0
Branch(config-if)#no shut

Branch(config)#int fa0/1
Branch(config-if)#no shut
Branch(config)#int serial0/0/0
Branch(config-if)#no shut

Now, the same procedure on router HQ:
HQ>enable
HQ#show ip int brief
HQ(config)#int fa0/0
HQ(config-if)#no shut

HQ(config-if)#int f0/1
HQ(config-if)#no shut

HQ(config-if)#int s0/0/0
HQ(config-if)#no shut
Using CDP protocol draw a topology diagram to learn which interfaces are connected between devices.

I am going to start my discovery on SW1, but feel free to start using any device in our topology. Here's what I find (you can click on the picture to enlarge it).

NOTICE!
Packet tracer does NOT support 'show interface status' command which allows me to find out which interfaces are enabled/disabled. So let me help you with an initial discovery a bit. PC1 and PC2 are already mapped in the topology diagram.

Let's add port identifiers in our topology.

SW1 port Fa0/3 connects SW2 port Fa0/3.
SW1 port Fa0/4 connects SW2 port Fa0/4.
SW1 port Fa0/13 connects Branch port Fa0/0.

This allows me to add the following port identifiers (connections) to my topology diagram:

Now, jumping over to SW2 to verify its neighbors.

There's nothing new here. Finally, I will see what neighbors Branch router recognizes.

This my final topology discovered:
On all switches shutdown the interfaces that are not currently used.

SW1(config)#int range fa0/1,fa0/5-12,fa0/14-24
SW1(config-if-range)#shutdown
SW1(config)#int range fa0/1,fa0/5-12,fa0/14-24
SW1(config-if-range)#shutdown