route from Rt1 before the variance is
configured. Serial 0/0 is the only route to 192.168.30.0.
Figure shows the output from show ip route from Rt1
after the variance is configured. The preferred route is
interface FastEthernet 0/0, but Serial 0/0 will also be used.
To verify load balancing, ping 192.168.30.1. After the
ping is executed the preferred route is using interface
Serial 0/0. IGRP will use load balancing between the two links.
Web Links Using the Extended ping and Extended
traceroute Commands http://www.cisco.com/en/US/tech/
tk826/tk365/ technologies_ tech_ note09186a0080093f22.shtml
Content 9.2 Network Testing 9.2.1
Introduction to network testing Basic testing of a
network should proceed in sequence from one OSI reference model
layer to the next. It is best to begin with Layer 1 and work to
Layer 7 if necessary. Beginning with Layer 1, look for simple
problems such as power cords plugged in the wall. The most
common problems that occur on IP networks result from errors in
the addressing scheme. It is important to test the address
configuration before continuing with further configuration
steps.Each test presented in this section focuses on network
operations at a specific layer of the OSI model. The commands
telnet and ping are two important commands that
are used for testing a network. Interactive Media
Activity Point and Click: Network Testing After completing
this activity, the student will be able to understand network
testing. Web Links Tools, Maintenance, and
Troubleshooting Tips for Cisco IOS Software
http://www.cisco.com/en/US/products/ sw/iosswrel/ps1828/prod_
troubleshooting_ technique09186a008010929b.html
Content
9.2 Network Testing 9.2.2
Using a structured approach to troubleshooting
Troubleshooting is a process that allows a user to find
problems on a network. There should be an orderly process to
troubleshooting based on the networking standards set in place
by an administration. Documentation is a very important part of
the troubleshooting process. The steps in this model are:
- Collect all available information and analyze the symptoms
of failure
- Localize the problem to within a single
network segment, to a single complete module or unit, or to a
single user
- Isolate the trouble to specific hardware
or software within the unit, module, or user’s network
account.
- Locate and correct the specific
problem.
- Verify that the problem has been
solved.
Figure shows another approach to
troubleshooting. Neither of these concepts are the only methods
to troubleshooting. However, the orderly process is of the
utmost importance in order to keep a network running smoothly
and efficiently. Using a structured approach to
troubleshooting, every member of a network support team can
know what steps each member of the team has completed to solve
a problem. If a variety of troubleshooting ideas are tried with
no organization or documentation, problem solving is not
efficient. Even if a problem is solved in the non-structured
environment, it will probably be impossible to replicate the
solution for similar problems in the future. Interactive
Media Activity Drag and Drop: Troubleshooting After
completing this activity, the student will be able to
understand show interface command. Web Links Tools,
Maintenance, and Troubleshooting Tips for Cisco IOS Software
http://www.cisco.com/en/US/products/sw/ iosswrel/ps1828/
prod_troubleshooting_ technique09186a008010929b.html
Content 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
Content
9.2 Network Testing 9.2.4
Layer 1 troubleshooting using indicators Indicator lights
are a useful tool for troubleshooting. Most interfaces or NICs
will have indicator lights that show whether there is a valid
connection. Often this light is called the link light. The
interface may also have lights to indicate whether traffic is
being transmitted (TX) or received (RX). If the interface has
indicator lights that do not show a valid connection, power off
the device and reseat the interface card. A faulty or incorrect
cable could also cause a link light to indicate a bad
connection or no link.Check to make sure that all cables are
connected to the appropriate ports. Make sure that all
cross-connects are properly patched to the correct location
using the appropriate cable and method. Verify that all switch
or hub ports are in the correct VLAN or collision domain, and
have appropriate options set for spanning tree and other
considerations. Verify that the proper cable is being used. A
crossover cable may be required for direct connections between
two switches or hubs, or between two hosts such as PCs or
routers. Verify that the cable from the source interface is
properly connected and is in good condition. If there is doubt
that the connection is good, reseat the cable and ensure that
the connection is secure. Try replacing the cable with a known
working cable. If this cable connects to a wall jack, use a
cable tester to ensure that the jack is properly wired. Also
check any transceiver in use to ensure that it is the correct
type, is properly connected, and is properly configured. If
replacing the cable does not resolve the problem, try replacing
the transceiver if one is being used. Always check to make sure
that the device is powered on. Always check the basics before
running diagnostics or attempting complex troubleshooting.
Web Links Installing and Troubleshooting Cabling and
Network Boards http://home.att.net/~s.k.vincent/ 801_3.htm
Content 9.2 Network Testing
9.2.5 Layer 3 troubleshooting using ping The
ping utility is used to test network connectivity. As an
aid to diagnosing basic network connectivity, many network
protocols support an echo protocol. Echo protocols are used to
test whether protocol packets are being routed. The
ping command sends a packet to the destination host and
then waits for a reply packet from that host. Results from this
echo protocol can help evaluate the path-to-host reliability,
delays over the path, and whether the host can be reached or is
functioning. The ping output displays the minimum,
average, and maximum times it takes for a ping packet to find a
specified system and return. The ping command uses