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| 6.3 |  | Troubleshooting Transport Layer Issues on Network Hosts |
| 6.3.2 |  | Gathering transport layer information on Windows machines |

Telnet
Although Telnet normally refers to an application layer protocol and program, it can be a useful tool for troubleshooting problems at other layers, particularly the transport layer. The usefulness of Telnet in troubleshooting comes from its ability to connect to a specific destination port on a remote server, allowing it to be used to confirm correct traffic flow from a client to remote server. Although never intended as a troubleshooting tool, Telnet is particularly useful for transport layer diagnostics.

Telnet can be run as either a command line utility or with a graphical user interface (GUI). Figure shows the command line Telnet application being used to confirm connectivity to a POP3 server.

ipconfig command
The ipconfig /all command can provide the network engineer with a lot of information about the configuration of a Windows-based machine. This information covers details from the MAC address at Layer 2, the IP address at Layer 3, NetBIOS information at Layers 4 and 5, to DNS information at Layers 6 and 7.