© ExplorNet’s Centers for Quality Teaching and Learning 1 Resolve common problems with wired and wireless networks. Objective – 2%

© ExplorNet’s Centers for Quality Teaching and Learning 2 Network Troubleshooting  In any network there are likely to be failures over time.  The larger, more complex the network the more likely there are to be problems.  To effectively solve problems a consistent approach should be taken.  Simplify as much as possible.  Use the OSI model as a checklist.

© ExplorNet’s Centers for Quality Teaching and Learning 3 Network Troubleshooting  If there are multiple devices exemplifying a problem try to isolate the devices first to simplify the situation.  Once the situation can no longer be simplified begin searching for the source of the problem.  Start at the lowest layer and work up the OSI model.  For example:  Start by checking wires and connections (Layer 1: Physical).  Next proceed to checking the NIC (Layer 2: Data Link).  Then check IP settings (Layer 3: Network).

© ExplorNet’s Centers for Quality Teaching and Learning 4 Software and Hardware Tools  To locate the source of the problem there are many tools that can be of assistance.  There are also tools that are more applicable to use once the source of the problem has been located.

© ExplorNet’s Centers for Quality Teaching and Learning 5 Hardware Tools  Cable Tester  Used to check network cables for continuity.  Checks each individual wire in a twisted pair cable.  Loopback Plug  Used to check a network interface.  Sends data directly back to the interface from which it comes.

© ExplorNet’s Centers for Quality Teaching and Learning 6 Hardware Tools  Toner Probes  Used to locate the end of a wire within a bundle of other wires.  Attach sender to known location.  Use receiver to locate other end.  Wireless Locator  Used to analyze the surrounding networks.  Good for determining signal strength.  Good for troubleshooting interference.

© ExplorNet’s Centers for Quality Teaching and Learning 7 Hardware Tools  Punch Down Tools  Useful if wire has come loose from a patch panel.  Cable Strippers  Removes the sheath of a wire so that the wire can be repaired.  Crimper  Allows for the attachment of an Registered Jack (RJ) tip.

© ExplorNet’s Centers for Quality Teaching and Learning 8 Software Tools  Ipconfig  Shows current IP addresses.  Can release and renew IP addresses.  Ping  Tests connectivity to an IP address.

© ExplorNet’s Centers for Quality Teaching and Learning 9 Software Tools  Tracert  Traces the route to an IP address.  Pathping  Combination of ping and traceroute.

© ExplorNet’s Centers for Quality Teaching and Learning 10 Software Tools  Netstat  Reports all active connections on an interface.  Nbtstat  Reports all hosts that are connected via NetBios.

© ExplorNet’s Centers for Quality Teaching and Learning 11 Software Tools  Net  Reports or assigns many network attributes depending on the options used.

© ExplorNet’s Centers for Quality Teaching and Learning 12 Common Symptoms & Solutions  Now that we have a troubleshooting method and a few tools we can take a look at some of the most common networking problems and their likely solutions. No connectivity Limited connectivity Local connectivity APIPA address Intermittent connectivity Slow transfer speeds Low RF signal IP conflict *Note that we cannot cover all possible problems or solutions because there are too many.

© ExplorNet’s Centers for Quality Teaching and Learning 13 No Connectivity Wired  This state occurs when there is a physical media problem or a bad network card.  Check the network cable first (layer 1) then troubleshoot the NIC (layer 2) if the cable is verified as working.

© ExplorNet’s Centers for Quality Teaching and Learning 14 No Connectivity Wireless  This state occurs if the WNIC has not been associated with a network.  Try to connect to a network.  If that fails check to make sure you have the proper wireless passphrase for the SSID you are attempting to connect to.  If there is still failure start at layer 1 and you have made sure there is no wireless interference. Then move to layer 2 and check the WNIC. Often improper WNIC drivers can cause this situation.

© ExplorNet’s Centers for Quality Teaching and Learning 15 LAN Connection, No Internet Access Limited Connectivity  Your PC is getting an IP address from the DHCP server, but there is no Internet access.

© ExplorNet’s Centers for Quality Teaching and Learning 16 LAN Connection, No Internet Access Local Connectivity Automatic Private IP Addressing (APIPA)  These two are very closely related.  When only local connectivity is available, the PC is not getting an IP address from a DHCP server even though it is configured to do so.  To make up for the lack of IP address, and so that the computer can communicate with other PCs on the network, it uses the reserved APIPA addresses which all begin with x.x.

© ExplorNet’s Centers for Quality Teaching and Learning 17 LAN Connection, No Internet Access When these previous situations occur:  Layer 1 and Layer 2 are ruled out because we have verified connection.  The problem lies with either a gateway router (layer 3) for Limited Connectivity or a DHCP server (layer 7) for Local Connectivity.  In either scenario, a check and reset of the device in question will likely fix the problem.

© ExplorNet’s Centers for Quality Teaching and Learning 18 Intermittent Connectivity  A situation in which your network state goes from connected to disconnect at random intervals.  This is often caused by a layer 1 problem.  A loose RJ-45 connector with a broken or damaged retention clip can be slowly slipping out of the NIC.  A wire that has been pulled on or pressured over a long period of time may be coming or is damaged.

© ExplorNet’s Centers for Quality Teaching and Learning 19 Slow Transfer Speeds  A situation in which your file transfers happen at speeds much lower than your specified bandwidth (i.e. 30 Mbps LAN transfer with a 100 Mbps NIC).  This is most often caused by Intermittent Connectivity.  If connectivity is verified as good, then check software settings for the NIC.  Auto Negotiation is the recommended setting for the NIC.

© ExplorNet’s Centers for Quality Teaching and Learning 20 Low Radio Frequency (RF) Signal  A situation in which the wireless connection exhibits either or both of the previous two behaviors because of a weak connection to the access point (AP)/router.  Solutions here center around layer 1, the physical connection.  Check to make sure that the AP/router was not moved.  The fewer walls between the PC and the AP/router the better the signal will be, if possible relocate the PC.  If the solution is not as obvious as above, the use of a Wireless Locator tool is very helpful in identifying sources of RF interference.  Try to eliminate as much RF interference as possible.

© ExplorNet’s Centers for Quality Teaching and Learning 21 IP Conflict  This situation occurs when two devices on the same network attempt to use the same IP address.  This most often occurs when a DHCP server is attempting to lease an IP address that has already been assigned statically by an administrator.  The solution is to change the DHCP server’s address range (often called a “scope”) to exclude the static IP address.

© ExplorNet’s Centers for Quality Teaching and Learning 22 Troubleshooting Flowcharts  Some times even following the logical troubleshooting process does not result in a solution.  Troubleshooting flowcharts can be very useful to make sure you did not overlook something simple.  A great network troubleshooting flowchart is available here: