Figure 3. Check that the ADSL and Power lights are on.
(note: Figure 3 is a generic figure, check your modem manufacturer for your specific status panel indicators. If your modem is a Cable modem then it will not have an ADSL link light.)
If the ADSL light is not on, check the phone connection. Ensure that the phone jack that connects to the modem is;
1. Physically well connected (clicked in)
2. It is plugged into an ADSL enabled phone line (this should be verified with your ADSL provider)
Verifying Layer 1 Summary. In this section we have checked power to all devices and checked that we have physical connections between the computer and the Internet modem. Physical connectivity can be verified by looking at link lights or, for advanced users, by accessing the device through its web interface and checking the interface status on the web interface. All physical links between the computer and the Internet must be connected and active in order for the internet to work.
If you have verified that all connections between the PC and the modem are connected and the Internet is still not working move onto Layer 2.
Troubleshooting an Internet Connection - Part 1 of 3
Troubleshooting an Internet connection is easiest if you use a structured approach. The approach detailed on this page uses the process of elimination to verify key components and then move onto the next. This approach works on any size network with any vendor.
Related Pages
The OSI (Open Systems Interconnection) model is a way of describing the connection between systems in terms of layers. By testing an verifying each layer one can narrow down the problem until the faulty component is found. Networks work on the first four layers of the OSI model so we will provide steps to troubleshoot these layers.
First four layers of the OSI model
- Layer 1 is the physical layer
- Layer2 is the Data Link layer
- Layer 3 is the Network layer
- Layer 4 is the Transport Layer
These are the layers that we should look at when the Internet is down.
Troubleshooting an Internet Connection Step 1- Verifying Layer 1.
Layer 1 of the OSI model is concerned with transporting bits between cables and network interfaces. Obviously, if we cannot transfer bits between systems, the Internet connection will not work.
Action1 . On a computer that is experiencing the broken Internet connection, open a command prompt by pressing Start -> Run -> type 'cmd', then inside the command prompt type ‘ipconfig /all’. Ensure that you do not see a ‘Media Disconnected’ message. If you do see this message it means that the cable between your PC and the network switch is either unplugged, broken or that the switch has no power.
C:\Documents and Settings\it-pathways>ipconfig /all
Windows IP Configuration
Host Name . . . . . . . . . . . . : it-pathways-pc221
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Unknown
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : it-pathways.com
Ethernet adapter Local Area Connection:
Media State . . . . . . . . . . . : Media disconnected
Description . . . . . . . . . . . : VIA Rhine II Fast Ethernet Adapter
Physical Address. . . . . . . . . : 00-1A-4D-72-D6-98
Figure 1. Media Disconnected means that there is no physical connection to your switch or modem
If you have a Media Disconnected message on your Local Area Connection - Check the connection from the PC
(note: if your PC connects through another interface such as a wireless adapter then you should check that adapter)
Checking the Local Area Connection
If the switch and the modem are separate devices, check that the switch is plugged into the Internet modem and that both devices have their link lights turned on (usually green, but sometimes orange depending on the link speed). If there are no lights on at all check that there is power to the device. If there are link lights on the switch or modem but no lights on the port that connect the devices the cable may be damaged or a crossover cable may be required.
C:\Documents and Settings\User>ipconfig /all
Windows IP Configuration
Host Name . . . . . . . . . . . . : it-pathways-pc221
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Unknown
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : it-pathways.com
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : it-pathways.com
Description . . . . . . . . . . . : VIA Rhine II Fast Ethernet Adapter
Physical Address. . . . . . . . . : 00-1A-4D-72-D6-98
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 192.168.1.101
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.254
DHCP Server . . . . . . . . . . . : 192.168.1.254
DNS Servers . . . . . . . . . . . : 192.168.1.254
Lease Obtained. . . . . . . . . . : Sunday, 30 May 2010 7:33:37 AM
Lease Expires . . . . . . . . . . : Sunday, 30 May 2010 7:33:37 PM
Figure 2. This is the output we normally see when the connection is working correctly. The Ethernet Local Area Connection adapter has acquired an IP address and has a DNS server, Subnet Mask and Gateway assigned.
Action 2. Check the connection between the modem and the Internet Service Provider
On the Internet modem, check that the modem indicates that the WAN link (the port that connects to the Internet, usually a phone line or cable) is online and that the light is switched on.
