| 9.2 |  | Network Testing |
| 9.2.3 |  | Testing by OSI layers |

| Testing should begin with Layer 1 of the OSI model and work to Layer 7 if necessary. Layer 1 errors can include: Broken cables Disconnected cables Cables connected to the wrong ports Intermittent cable connection Wrong cables used for the task at hand (must use rollovers, crossover cables, and straight-through cables correctly) Transceiver problems DCE cable problems DTE cable problems Devices turned off Layer 2 errors can include: Improperly configured serial interfaces Improperly configured Ethernet interfaces Improper encapsulation set (HDLC is default for serial interfaces) Improper clockrate settings on serial interfaces Network interface card (NIC) problems Layer 3 errors can include: Routing protocol not enabled Wrong routing protocol enabled Incorrect IP addresses Incorrect subnet masks If errors appear on the network, the process of testing through the OSI layers should begin. The ping command is used at Layer 3 to test connectivity. At Layer 7 the telnet command may be used to verify the application layer software between source and destination stations. Both of these commands will be discussed in detail in a later section.
| Interactive Media Activity Matching: Testing with the OSI layers After completing this activity, the student will be able to understand the OSI layers.
| Web Links General Troubleshooting Tools http://www.nwnetsmart.com/ns/books/ ciscopress/samples/ 1578700922.pdf