Lesson 12	Network diagnostic tools
Objective	Describe how to troubleshoot Internet problems.

Network Diagnostic Tools

Having all the proper pieces in place and hooked up is no guarantee of continuous, trouble-free connections. Problems can occur; for example, you may not be able to connect to the host.

1) PING is a command used to test whether a remote host can be reached from a specific computer. This most basic TCP/IP utility is also used to test network connections or applications. When one computer pings another computer, information is sent and received that lets the sending computer know if its information is being received.

2) WINIPCFG is a Windows 95/98-specific utility used to provide information about IP addresses, network connections, and Internet resources. The Windows version of WINIPCFG is called IPCONFIG.

3) ARP is a command sent to a router and is used to display the contents of the Address Resolution Protocol (ARP) table. ARP is employed by system technicians to detect whether any nodes on the network may have been configured with the wrong IP address.

4) Tracert (pronounced tracer-tee) is a program that shows routing and delay times over the Internet from your PC to a destination computer such as bing.com. It displays several columns of numbers, which represents a connection or hop from one router to another. It's useful for determining where a delay may be occurring: ISP, destination site, or some hop along the way.

5) Netstat displays a list of server-side TCP/IP connections. The output includes a list of addresses corresponding to open incoming connections. Use Netstat to obtain network statistics, display the contents of the local routing table, and to obtain statistics on a particular protocol such as TCP.

PING is a command used to test whether a remote host can be reached from a specific computer.
WINIPCFG is a Windows 95/98-specific utility used to provide information about IP addresses, network connections, and Internet resources.
ARP is a command sent to a router and is used to display the contents of the Address Resolution Protocol (ARP) table.
Tracert (pronounced tracer-tee) is a program that shows routing and delay times over the Internet from your PC to a destination computer such as bing.com
Netstat displays a list of server-side TCP/IP connections.

You can diagnose problems using a variety of network diagnostic tools. These tools are available as command-line driven utilities and/or utilities with a graphical user interface. When one tool is available in both formats, you can choose whichever suits you best.
In the next lesson, you will learn when to use network analyzers.

Network Diagnosis with Nagios

With personnel resources becoming more and more scarce, no IT department can really afford to regularly check all systems manually. Networks that are growing more and more complex especially demand the need to be informed early on of disruptions that have occurred or of problems that are about to happen. Nagios, the Open Source tool for system and network monitoring, helps the administrator to detect problems before the phone rings off the hook. The aim of the software is to inform administrators quickly about questionable (WARNING) or critical conditions (CRITICAL). What is regarded as questionable or critical is defined by the administrator in the configuration. A Web page summary then informs the administrator of normally working systems and services, which Nagios displays in green, of questionable conditions (yellow), and of critical situations (red). There is also the possibility of informing the administrators in charge, depending on specific services or systems, selectively by e-mail but also by paging services such as SMS. By concentrating on traffic light states (green, yellow, red), Nagios is distinct from network tools that display elapsed time graphically (for example in the load of a WAN interface or a CPU throughout an entire day) or that record and measure network traffic. Nagios is involved plainly and simply with the issue of whether everything is on a green light. The software does an excellent job in looking after this, not just in terms of the current status but also over long periods of time.