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Solving for the Physical ...
05 February 09

# Solving for the Physical Topology Using a Logical Topology

Posted byINE

We see our students at all levels sometimes struggle building a network from the "ground-up" using a logical topology diagram. Let us use this blog post to examine a portion of a logical diagram and discuss how one could most easily and accurately setup the network.

Here is a typical section of a typical logical diagram from one of our practice labs. The first mistake a student typically makes is assuming that R1 and BB2 are directly connected. Do not forget, to form this Ethernet segment, at least one switch is used to connect R1 and BB2, and the switch(es) may feature any amount of initial configuration. The switch is not shown on the diagram for simplicity, and you will possess the tools to discover the missing devices easily.

Let me provide a simple set of steps that I would use to ensure this portion of the network is built correctly.

Step 1: I go to R1 Fa0/0 and carefully add the correct IP address and issue the no shutdown command.

Step 2: Use the show cdp neighbor command on R1 to learn the remote port that Fa0/0 connects to.

Step 3: Move to this device, create VLAN 12 if needed, and ensure to place the port that connects to R1 Fa0/0 in VLAN 12 using the switchport access vlan 12 command.

Step 4: Use the show cdp neighbor command on this switch to determine the port connected to BB2. Place that port in VLAN 12.

Step 5: You can now attempt to ping the BB2 device. NOTE: It is typical in the actual lab for backbone devices to block ping attempts. So in the lab exam, be sure to do every verification that is possible except the ping. Hopefully later in the lab you will Layer 3 peer with the device and can confirm connectivity through the receipt of routes.