| A | B |
|---|
| Layer 1 (1) | DTE cable problems |
| Layer 3 (1) | incorrect DNS to IP bindings |
| Layer 2 (1) | serial interfaces configured improperly |
| Layer 3 (2) | incorrect IP addresses or incorrect subnet masks |
| Troubleshooting Resources (1) | experts |
| Layer 1 (2) | cables connected to the wrong ports |
| Layer 2 (2) | improper clockrate settings on serial interfaces |
| Layer 3 (3) | wrong routing protocol enabled |
| Layer 1 (3) | transceiver problems |
| Troubleshooting Resources (2) | web resources |
| Layer 1 (4) | devices are not turned on |
| Layer 2 (3) | ethernet interfaces configured improperly |
| Layer 3 (4) | routing protocol not enabled |
| Layer 1 (5) | broken cables |
| Layer 2 (4) | wrong ecapsulation set |
| Troubleshooting Resources (3) | IOS commands |
