Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

Troubleshooting the Application Layer 169
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HyperText Transfer Protocol (HTTP) HTTP allows computers to exchange
files in various formats on the WWW through client software called a
Web browser. The HTTP protocol uses TCP port 80 to send and receive
information to Web servers and clients.
Network News Transfer Protocol (NNTP) NNTP is used for managing
messages posted to private and public newsgroups. NNTP servers provide
storage of newsgroup posts, which can be downloaded by client
software called a newsreader. The NNTP service defaults to using TCP
port 119.
DNS The DNS is a distributed database that is used by most of the
other applications in the TCP/IP protocol suite to resolve hostnames to
IP addresses. The DNS service defaults to using TCP port 53.
DHCP The DHCP is used to dynamically assign TCP/IP addresses and
additional configuration information to clients and servers. IP addressing
information is leased by a DHCP server for a specific period of time, usually
3 days, before the lease must be renewed by the client. You can use the ipconfig/release
and ipconfig/renew commands to refresh the DHCP configuration
on a particular workstation.
Summary of Exam Objectives
In this chapter, we talked about the different troubleshooting tools available for
you to track down and isolate connectivity problems on your network. We started
by looking at the importance of having an overall framework or methodology for
tackling networking issues. Before you think about the different tools available
for troubleshooting, you first need to determine what the problem actually is. To
do this, you need to gather as much information as possible from your users, as
well as gathering information from system logs of any devices that are having the
trouble.
To help you further isolate the cause of a problem that you’re troubleshooting,
you have a number of utilities available in the Windows and Linux operating
systems. To test basic TCP/IP connectivity between two hosts, you can use the
ping command. You can also use the tracert command on a Windows computer
or traceroute on Linux to view the actual path that network traffic takes between
two hosts. On Windows Vista, XP and 2000, you can use the pathping command,
which combines the features of ping and tracert into a single utility.
To troubleshoot name resolution issues, you can use nslookup on a Windows computer
and dig on Linux. These commands will allow you to verify that your DNS
servers are functioning properly and have the correct information with which
to answer client queries. For Windows-based computers that rely on NetBIOS,
you can use the nbtstat command to troubleshoot NetBIOS name resolution.
To troubleshoot the physical components of your network, including network
cables and wall jacks, you should also be familiar with the purpose of an Ethernet
crossover cable, as well as cable testers that are designed to test Ethernet cables
for flaws or breaks.