Troubleshooting Internet Connectivity

If you can’t connect to the internet when you think you should be able to, there are a few things you should try.

In a typical setup, a home computer connects to it through a broadband router or modem. This can be a wireless or a wired connection. The methods are the similar. In the case of a wire, the first thing you should test for is whether the computer is physically connected to the modem. Check the connections are plugged in properly and there are no breaks in the wire. Similarly, is the modem itself connected to the internet? If you have a spare computer, does the modem work on that?

In the diagram below, the connection A-B is from the computer to the modem and the connection B-C is from the modem to the internet. The computer should be able to reach C through B.

Computer, A Modem, B Internet, C

If there are no obvious reasons why this is not happening, such as a loose wire, the next step is to send packet of information from the computer A to the modem B. This method is known as pinging the modem. If there is nothing blocking them, the packets can be returned or echoed back to the computer, from B to A. If on the other hand the packets cannot reach the modem, they will not be returned to the computer and will be lost in transit.

To ping the modem, you will need to know its IP address. IP stands for Internet Protocol and an IP address is an address on the network that is usually unique and can be used as a postman uses a house address to deliver letters to. This can differ from modem to modem. I’m on Virgin Media and mine is 192.168.100.1. BT Home Hubs commonly use 192.168.1.254. If you do not know yours, your Internet Service Provider (ISP) should be able to tell you what it is, though they usually expect only their technicians to need to know it.

To ping your modem, you will need to open a command-line prompt. Taking Windows Vista as an example, you click on the Start button in the bottom left corner of the screen, then type CMD into the box which appears above it. The box is the one with “Start Search” in it. Type CMD over this and hit return. In Windows XP, click Start followed by Run, then type CMD in the box. After maybe a few seconds, a command line prompt window will open. You will use this to ping the modem.

At the prompt, type PING followed by a space followed by the IP address of your modem, then hit Return. You can type in upper- or lower- case. It does not matter here.

One of two things will happen. Either the PING will be successful, in which case you know that the computer can communicate with the modem, or it will be unsuccessful, in which case something is blocking the connection. How do you know whether it is successful or unsuccessful? You examine the messages which appear.

Below is the result of a successful PING. Here I am pinging with my modem connected:

>ping 192.168.0.1

Pinging 192.168.100.1 with 32 bytes of data:

Reply from 192.168.100.1: bytes=32 time=1ms TTL=64

Ping statistics for 192.168.100.1:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

Minimum = 1ms, Maximum = 1ms, Average = 1ms

Notice that four packets have been sent, four packets have been returned and no packets have been lost. The computer can communicate with the modem.

Now I disconnect my modem and try pinging it again:

Pinging 192.168.100.1 with 32 bytes of data:

Destination host unreachable.

Ping statistics for 192.168.100.1:

Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Notice that this time, four packets have been sent, none returned and four lost. The computer cannot communicate with the modem.

Why? There are a couple of common reasons. One is the presence of a firewall. A firewall is designed as a security measure to prevent unauthorized access to your computer. Some versions of Windows have them. Some anti-virus programs and internet security solutions also have them. Incorrectly configured firewalls can block an internet connection.

Another thing worth checking is the properties of the network connection. In Vista, go to

Start->Network->Network and Sharing Centre->Manage Network Connections,

then right-click the network connection and select Properties from the menu that pops up. Highlight “Internet Protocol Version 4 (TCP/IPv4)”, and then click Properties. Leave version 6 alone.

In the diagram above, I have entered values into the boxes. This is because this computer connects to the internet via another computer on my home network. In the situation where the computer is directly connected to the modem, only “Obtain an IP address automatically” and “Obtain the following DNS server address automatically” should be selected. Addresses will be obtained automatically from your ISP via the modem.

To check that this is the case, open a command-line prompt as described above and type IPCONFIG /ALL. This lists the IP addresses of all your network adapters. Usually you will only have one network adapter and that is the one that connects to your modem. Because I am on a home network, I have two listed. An example is shown below. For security reasons, I have changed some values. I have two network adapters listed, Realtek and VIA Rhine III Fast Ethernet adapter. The Realtek adapter connects to the internet. Can you find its IP address?

Windows IP Configuration

Host Name . . . . . . . . . . . . : presario

Primary Dns Suffix . . . . . . . :

Node Type . . . . . . . . . . . . : Hybrid

IP Routing Enabled. . . . . . . . : Yes

WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Realtek:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : Realtek RTL8139/810x Family Fast Ethernet NIC

Physical Address. . . . . . . . . : 00-0D-77-43-49-E6

Dhcp Enabled. . . . . . . . . . . : Yes

Autoconfiguration Enabled . . . . : Yes

IP Address. . . . . . . . . . . . : 92.233.122.78

Subnet Mask . . . . . . . . . . . : 255.255.254.0

IP Address. . . . . . . . . . . . : fe80::20c:76ff:fe44:49e6%4

Default Gateway . . . . . . . . . : 92.233.122.1

DHCP Server . . . . . . . . . . . : 62.31.144.119

DNS Servers . . . . . . . . . . . : 194.178.4.100

194.178.8.100

fed0:0:0:ffff::1%1

fed0:0:0:ffff::2%1

fed0:0:0:ffff::3%1

Lease Obtained. . . . . . . . . . : 21 May 2009 07:48:39

Lease Expires . . . . . . . . . . : 25 May 2009 07:23:06

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : VIA Rhine III Fast Ethernet Adapter

Physical Address. . . . . . . . . : 00-40-E4-7C-C5-AD

Dhcp Enabled. . . . . . . . . . . : No

IP Address. . . . . . . . . . . . : 192.168.0.1

Subnet Mask . . . . . . . . . . . : 255.255.255.0

Default Gateway . . . . . . . . . :

DNS Servers . . . . . . . . . . . : 192.168.0.1

Tunnel adapter Teredo Tunneling Pseudo-Interface:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface

Physical Address. . . . . . . . . : 80-00-FB-6A-A3-15-84-BB

Dhcp Enabled. . . . . . . . . . . : No

IP Address. . . . . . . . . . . . : fe81::ffff:ffff:fffd%5

Default Gateway . . . . . . . . . :

NetBIOS over Tcpip. . . . . . . . : Disabled

Tunnel adapter 6to4 Tunneling Pseudo-Interface:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : 6to4 Tunneling Pseudo-Interface

Physical Address. . . . . . . . . : 5C-EB-7B-44

Dhcp Enabled. . . . . . . . . . . : No

IP Address. . . . . . . . . . . . : 2002:5cea:7b44::5cea:7b44

Default Gateway . . . . . . . . . : 2002:c058:6301::c058:6301

DNS Servers . . . . . . . . . . . : feb0:0:0:ffff::1%1

feb0:0:0:ffff::2%1

feb0:0:0:ffff::3%1

NetBIOS over Tcpip. . . . . . . . : Disabled

Tunnel adapter Automatic Tunneling Pseudo-Interface:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : Automatic Tunneling Pseudo-Interface

Physical Address. . . . . . . . . : C0-B8-00-01

Dhcp Enabled. . . . . . . . . . . : No

IP Address. . . . . . . . . . . . : feb0::5efe:192.168.0.1%2

Default Gateway . . . . . . . . . :

DNS Servers . . . . . . . . . . . : feb0:0:0:ffff::1%1

feb0:0:0:ffff::2%1

feb0:0:0:ffff::3%1

NetBIOS over Tcpip. . . . . . . . : Disabled

Tunnel adapter Automatic Tunneling Pseudo-Interface:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : Automatic Tunneling Pseudo-Interface

Physical Address. . . . . . . . . : 5C-EB-8B-44

Dhcp Enabled. . . . . . . . . . . : No

IP Address. . . . . . . . . . . . : fe80::5efe:92.244.123.68%2

Default Gateway . . . . . . . . . :

DNS Servers . . . . . . . . . . . : feb0:0:0:ffff::1%1

feb0:0:0:ffff::2%1

feb0:0:0:ffff::3%1

NetBIOS over Tcpip. . . . . . . . : Disabled

Its IP address is 92.233.122.78, given by the line:

IP Address. . . . . . . . . . . . : 92.233.122.78

It is the IP address of the Realtek network adapter, the one that connects to the internet. Don’t worry about all the rest of the stuff like tunnels.

Why is this significant? It means that it has obtained (known as leasing) an IP address from the ISP and can therefore connect to the internet. Sometimes if it can’t obtain an IP address from an external server, it allocates itself an IP address. This is known as Automatic Private IP Addressing. The Internet Assigned Numbers Authority (IANA) has reserved 169.254.0.0 through 169.254.255.255 for Automatic Private IP Addressing. Any IP address within this range is an Automatic IP Address. This may occur if an IP address cannot be obtained from your ISP, if your internet connection is down, for example. Automatic Private IP Addresses are private. They are not valid on the internet.

Some modems/routers need to be encouraged to renew their IP addresses. For example, if your internet connection has been down and has been restored, you don’t want your computer to hang onto an Automatic Private IP Address, because it is only recognized on the internal/home network. To release the old IP address and obtain a new one (known as renewing the lease), type IPCONFIG /RELEASE followed by IPCONFIG /RENEW at the command-line. Unplugging the modem for a few seconds can have the same effect, but you should try both methods.

If all this fails, there could be a firewall blocking your internet access. A firewall can be part of Windows itself or an anti-virus program. Incorrectly configured firewalls are a common source of loss of connectivity.

It is not feasible to discuss in detail every firewall configuration of every internet security and anti-virus program, so I will use Norton 360 Version 3 as a brief example of how to check your security settings. For other and more detailed solutions, you will need to read the documentation of whichever anti-virus or other security program you have. If you turn off any security setting, it may leave you vulnerable to a hacker attack. If you want to be safe, you should disconnect connection B-C in the first diagram above when turning off firewall settings. This will commonly be a co-axial cable going into your modem, but will depend on your individual set-up. If you are using a BT Hub for example, it will be an extension of your phone line going into the modem/router through a splitter. Even with B-C disconnected, you should still be able to ping the modem over connection A-B.

Now you are ready to experiment with your security settings. If you have an internet security program such as Norton, open it. Using Norton 360 as an example, its interface will look like this:

Click “Settings” at the top.

From this panel, you can turn on or off firewall settings. When you turn off a setting, try to ping the modem again. Keep experimenting with the settings until you can ping the modem. Change one setting at a time, until you can ping the modem. If you still cannot ping it, disable all security settings. Norton gives you the option of doing this for a default of 15 minutes, but you can make it longer. It will warn you while you are unprotected. In the diagram below, I am about to turn off my Smart Firewall for fifteen minutes. You can select a longer period of time or until system reboot, but don’t forget to turn it back on if necessary as soon as you connect to the internet.

Some security programs such as Norton use their own firewall instead of Windows’ firewall. If you try to turn on the Windows firewall (by going to Start->Control Panel->Windows Firewall) with Norton installed, you will get this message:

Finally, most Broadband routers and modems I have come across have a user interface you can log onto. If you can ping your modem, try to connect to this. You do this try typing in the IP address of the modem into the address bar of a browser like Internet Explorer. As I have said, you need its IP address. Ask your ISP if you’re not sure. You will most likely be presented with a logon screen and some options like this:

For security reasons, I have erased some information such as my password and MAC address from this screenshot.

Once you log in, you can access other diagnostic information such as power levels, but this is only useful if you can connect to your modem in the first place. If you can’t, you should follow the all the steps I described.

I hope you have found this document informative and easy to understand. I have tried to avoid using technical jargon wherever possible, not an easy task when trying to describe something as technical as this.

If you have any comments, I would appreciate them. You can email me from my home page: www.mammothobsequious.com.

While you’re there, have a look at my other stuff.

Oh, and I almost forgot to mention it because it’s so obvious, have you scanned your computer for viruses that may be blocking your internet connection?

Of course, if you can’t update your anti-virus program or run it because a virus already on your computer is stopping it, then it’s too late and you have another common problem on your hands.

If you want a solution to that, email me. If I get enough of them, I’ll write a guide for that.

Danny Crossley.