Several good tools are available for debugging a network at the TCP/IP layer. Most give low-level information, so you must understand the main ideas of TCP/IP and routing in order to use the debugging tools.

On the other hand, network issues can also stem from problems with higher-level protocols such as DNS, NFS, and HTTP. You might want to read through Chapter 13, TCP/IP Networking, and Chapter 14, Routing, before tackling this chapter.

In this section, we start with some general troubleshooting strategy. We then cover several essential tools, including ping, traceroute, netstat, tcpdump, and snoop. We don’t discuss the arp command in this chapter, though it, too, is a useful debugging tool—see page 286 for ...

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