Mostly home computer networks in home do not have troubleshooting tools such as LAN-Tester or Multi-meter. Your network will not run as smooth as you expect to be in its best performance forever, once you might experience some problems such as network connection problem. Should you experience such network connection problem, how can you perform a network troubleshooting?
Network troubleshooting for experienced network engineer in enterprise class networks typically use many types of troubleshooting tools such as network management tool to detect the failure nodes, LAN tester, multi-meter etc. In home computer network (mostly users with less networking experiences), you don’t need such complicated tools because your home network is not as complicated as those enterprise class networks. See also LAN topology.
The following figure 1 shows a simple wired computer network diagram in homes or small offices. The modem-router connects to the internet via the local loop cable to the ISP and the modem connects to the LAN Switch via a cross network cable. PC-A connects to the switch (port#1) via network cable A, PC-b connects to the switch (port#7) via network cable B. There are many situations when you need to perform a network troubleshooting.
A> PC-A cannot access the internet but PC-B can
In this scenario, PC-A cannot access the internet but PC-B can. PC-B can browse the Internet with no problem. This means:
- Internet services is no problem
- The Switch is likely no problems
- No problem with the modem
Network troubleshooting steps you need to perform is to suspect the NIC adapter, the Switch port, or the network cable:
a. NIC disabled
Verify that the NIC adapter of PC-A is not disabled. Verify that you can see local connection icon in the bottom right-corner of your screen. If you cannot see it, it is likely that your NIC adapter is disabled accidently. In Windows XP, click start > control panel > double click Network Connections icon > see if the connection icon is marked as disabled as shown in figure 2.
Figure 2 - lan connection icon and disabled status
When the NIC adapter is disabled, the icon looks grey. Right click the icon and then select Enable. You will see the local connection icon on the bottom right-corner of your screen.
You can also test using the ‘ipconfig /all’ command from the command line. Enter the command line interface (by pressing the windows button and the ‘R’ button at the same time and type CMD then press Enter. Or you can click Start > Run > type ‘CMD’ and then press Enter) and type: ipconfig /all and see if you can see the NIC adapter status something like this:
Windows IP Configuration Host Name . . . . . . . . . . . . : TOWER Primary Dns Suffix . . . . . . . : Node Type . . . . . . . . . . . . : Unknown IP Routing Enabled. . . . . . . . : No WINS Proxy Enabled. . . . . . . . : No Ethernet adapter Internal LAN: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Realtek RTL8139 Family PCI Fast Ethernet NIC #2 Physical Address. . . . . . . . . : 00-1C-F0-B9-F2-A9 Dhcp Enabled. . . . . . . . . . . : No IP Address. . . . . . . . . . . . : 192.168.1.25 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.1.1 DNS Servers . . . . . . . . . . . : 202.134.1.10Or you can type the ‘ping localhost’ or ‘ping 127.0.0.1’ from command line and see if you get the successful response. If you get the request time out, the adapter is faulty or disable.
b. Switch Port Problem
PC-A cannot connect to the internet can be caused by the faulty port of the switch. Generally the Switch includes the LED indicators for each of the ports, when the port is active with the link, it will be on.
Trace the cable from PC-A to the switch port (in this case pport#1) and see if the LED indicator for the corresponding port is on. Unless, unplug the cable and move to different unallocated port for example port#2 and see if the LED for this port is on. If you can confirm that the LED for port#2 in on, then you can confirm that switch port#1 is faulty. Mark the faulty port with ‘faulty’ sign.
c. Faulty Cable
If you are not successful in step b, you can suspect that the network cable is faulty. Swap cable-A with Cable-B (taken from PC-B) and connect PC-A with cable-B to the switch and see if you can see the LED port#1 is on for PC-A. If the LED is on for PC-A, you can confirm that cable-A is faulty. Mark the cable-A with ‘faulty’ and replace with new one.
B> All the PC cannot access the Internet
If you find that all the PCs cannot access the internet, probably you have:
- the Switch problem, or
- the modem problem, or
- cable connection from the switch to the modem, or
- the ISP problem.
If you can see that LEDs correspond to the allocated ports are ‘ON’ or active, you can suspect that something wrong with the cable between the switch and the modem. Unplug the cable and plug it again firmly both at the modem and the switch and see if the PCs can access the internet. You can also see the LED indicator in the modem (if available) for the Ethernet port if it is ON. If the light is off, replace the cable with a new one (cross UTP cable). But if you find that LED indicator is ON but you still cannot access the internet, make a phone call to your ISP if the internet is out of services.
These simple steps in performing network troubleshooting in this article is actually for simple network in home environment, but the concept can be applied to large environments.
By Ki Grinsing
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