Configuring Cable Modems, DSL & Home Routers

How to get the Darn things to Work !!

On this page we give you the most common causes & fixes for Cable/DSL internet access problems.  

Are you stuck?  OK, here's what you do:
1)  read this page first - and if still no luck . . .
2) go to this very detailed troubleshooting site (excellent!!) :
                           NTLworld's Cable Modem Troubleshooting Tips  
3)  if still not up and running, try Microsoft's Internet Connectivity troubleshooting page

These days, everyone and their brother are getting either Cable or DSL service.  And many of those people have home LAN's (Home Local Area Networks).  The tech support of the Cable companies are staffed by trainees mostly, and they can't help you other than to have you do an "ipconfig /all" in DOS  !!  

***  by the way, you will see the term NIC used in this article.  NIC = Network Interface Card, which it your PC's Ethernet card). 

Here's the deal  .  .  .   Hubs also act as repeaters.  They regenerate signals - amplify and reshape them into nice square waves at a specific power level.  The cable and DSL modems also double as repeaters - but they are not always as good at it as hubs.  Hubs have to operate in all sorts of conditions . . . 100 meter cable runs, connections with many different router, switch vendors, etc.  So they are made for weak signals - and have been through a 20 year development cycle.  This is why so many have fixed their high-speed Internet access by placing a hub or switch between the Modem and Router .  .  .  and doing that is one of the steps outlined here - it is often the step that makes the difference.

My own Story

I will tell you this, because what happened to me - has happened to many.  My sideline is computer repair (PCdoc), so I figured that changing to high-speed cable Internet access would be a snap - especially for me - the expert.  How wrong I was !!!  And once I fixed my own problem . . . I saw the same problem several times out in the field, and luckily knew how to deal with it.

Like everyone else, for years I endured slow, pokey, dial-up Internet service with Earthlink.  My home is far from the nearest CO, so DSL (and even ISDN) was not available.  Finally, my cable provider upgraded their system and began offering 2-way Internet access.  But the installation and configuration was a 10-day nightmare - which finally ended when I placed a hub in between the Cable Modem and Router.  But in the end everything worked perfectly - and what a difference it made !!!  I had 3 workstations with blazing Internet access, and a Laptop with a lightning-fast wireless connection to the Internet.  In addition, all computers communicated with each other, and could print to either of my two printers.  It was well worth the many days of troubleshooting.

Proving the Cable Modem was OK  -  Initially, after a couple of days of troubleshooting, and finding out that I needed to Clone my PC's NIC card MAC address to my Router's WAN interface  .  .  .  finally, connecting the modem directly to my PC worked fine, and it assigned a DHCP IP address to my PC without fail.  This proved that the cable modem was working.  

The main Problem - the Router WAN port DHCP assignment from the Cable Modem  -  but my LinkSys BEFW11S4 V2 router simply could not receive the DHCP assigned IP address from the Motorola Surfboard SB5100 Cable Modem !!!  I tried everything !!! 10 days of troubleshooting.  I looked up my PC's MAC address, and cloned it to the router, as is required.  I flashed the firmware to the latest - and even tried older firmware versions.  But every time I went into the router's config (using IE with an address of and clicked "Release IP address" then "Renew IP address" - all I got was all zeros !!

Static IP Addressing Workaround - I was able to temporarily get it to work by connecting the cable modem directly to my PC (which worked fine), writing down all the addresses, re-inserting the router, and setting all the addresses using the router's Static IP option.  But since Adelphia changes your IP address several times a day, this was only a temporary kludge.

Inserting a Hub - the final Fix - in desperation, I began to think about what could cause my PC to fail at receiving it's assigned IP address from the DHCP server (the cable modem).  Maybe the signal was just weak ??  So I tried amplifying the signal by inserting an active hub in between the modem and router.  

One last Glitch - at first inserting the hub did not work. The cable modem port is DCE, while the LAN ports on the hub are also DCE, and as we said - DCE-to-DCE does not work !!   Well, I could have used a crossover cable, but there is a special port on the hub, called an uplink port.  Almost all hubs have an uplink port, which is a direct connection to the last LAN (DCE) port - but the connections are flipped, which makes it a DTE port.  So, the uplink port is a hard-wried, mirror-image of the LAN port.  This special port . . . . the uplink port - is made for the very purpose of connecting to another DCE device.  

NOTE:  the reason this port is called the uplink port, is that it allows you to connect the hub to a device which is upstream (closer the the core of the network, and away from the customer), such as a router or a larger hub.  

But for some unkown reason, it simply would not work !!!  To this day, I have never figured out why !!!  The uplink port is supposed to be a simple reversal of the wiring of the last LAN Port, which converts it from DCE to DTE.  This is why the manufacturer tells you that you cannot use both port 4 and the Uplink port - you must use one or the other - NOT BOTH !!  So it should have worked.  In desperation - although it is the same identical wiring connectivity - I tried using the 4th LAN port on the hub, which is reverse wired from the uplink port, which means it is DCE, and requires a crossover cable (since the hub's LAN port to the Cable modem port is DCE-to-DCE).  It worked perfectly !!!  See the third, bottom configuration below. 

3 Configurations to get you up and Running

The diagram below show you the three possible connections you can use for your Internet access with a router to support multiple computers on one Internet connection.  If you have only one PC then take out the router from the configuration.

If this does not work - then follow the 9 Steps below !!!


Hubs Explained

there are two types of hubs:

NOTE:  active hubs are far superior to passive hubs.  However, they used to be rather expensive, and at that time, most home LAN connections were 10 Mbps Ethernet, so the inexpensive, mini-hub (passive) was an excellent choice .  But today active mini-hubs are so cheap, that it is difficult to even find a passive hub for sale.

Some Cable and DSL modems, as well as home LAN routers, strictly require a specific signal strength to operate properly.  It is not uncommon for a home to have a weak Cable/DSL Internet signal  strength.  This can be due to a long distance from the CO, a noisy environment, or because the signal is being split between too many homes at the aggregation point.  

Normally you connect the cable/dsl modem directly to the router, and all is well.  Typically, the only reason you would need a separate hub is if you need to connect multiple workstations together - but today's home routers also act as a hub, and they usually have 4 ports, which negates the need for an external hub.  

However, if your Internet signal is weak, then you can insert a hub - and in this case you would be using the hub for one reason only - signal regeneration !!  Inserting a hub in between the modem and router will regenerate the weak signal in BOTH DIRECTIONS - so that the modem and the router can read the data accurately.  

In conclusion - if your Internet connection is failing due to weak or noisy signals, then inserting an active hub between the modem and router will fix the problem !!!  The only possible exception to this, is when the signal is so weak that it cannot be accurately regenerated - but this is rare.  


The 9 Steps to get your Cable/DSL Modem and Router to Work

1)  Make sure the Cable Modem or DSL works while Directly Connected to your PC

connect the unit to your NIC, and try to browse the Internet

if it does not work, then call your Cable company - they should be able to get this part working

if it does work - then THE CABLE/ DSL MODEM IS FINE !!!

then unplug the cable, and take two Ethernet cables :

2)  Clone the MAC Address into the Router

Some providers require the cable modem to have a "cloned" MAC address (physical address), that is the same as your Ethernet card.  For most routers, they can be accessed from your Browser, and by typing in the address of the router, usually:

NOTE: if this does not work, try removing the close setting and repeating all of these steps.  Alternatively, you may be lucky enough to get someone from the Cable or DSL company to answer the question of whether or not their service requires this !!!

3)  Configure your NIC to 10 Mbps Half-Duplex

Although most NIC's are 100/10 Mbps, cable modems, and the WAN port of most home routers will not allow more than 10 Mbps.  By default, many NIC's install and configure themselves at 100 Mbps.  To change ot to 10 Mbps half duplex :


  1. Control Panel/System/Hardware tab  .  . . Device Manager
  2. click the plus symbol next to Network Adapters
  3. double-click on your NIC (Network Interface Card) to go to Properties
  4. click the Advanced tab, and select "Media Type" from then list of Properties
  5. click the drop-down arrow next the "Value" - you will see the speed settings
  6. select 10BaseT_Half_Duplex if available  -  if not, select 10BaseT - different cards have different names, but they should have 4 settings  .  .  .  100 Mbps Full Duplex, 100 Mbps half duplex, 10 Mbps Full Duplex, and 10 Mbps half Duplex.  Select the one that will result in 10 Mbps half-duplex
  7. click OK
  8. repeat for all machines that you plan on connecting to your router


  1. right-click on Network Neighborhood and select Properties
  2. double-click on your Network Card in the list
  3. click the Advanced tab, and select "Media Type" from then list of Properties
  4. click the drop-down arrow next the "Value" - you will see the speed settings
  5. select 10BaseT_Half_Duplex if available  -  if not, select 10BaseT - different cards have different names, but they should have 4 settings  .  .  .  100 Mbps Full Duplex, 100 Mbps half duplex, 10 Mbps Full Duplex, and 10 Mbps half Duplex.  Select the one that will result in 10 Mbps half-duplex
  6. click OK
  7. repeat for all machines that you plan on connecting to your router


4)  Restart all 3 Devices in this Order

  1. unplug the power from your Router
  2. unplug the power from your Cable Modem
  3. power down your PC
  4. plug the power cable back into your cable modem - wait until all lights are ON
  5. plug the power cable back into your Router - wait until the indicator lights are ON
  6. boot up your PC

5)  Test the connection - Surf The Web !!!

test your Internet connection by surfing the web

6)  Connect up your other PC's

plug your other machines into the LAN ports on the Router

boot them up and test by surfing the web

7)  Place a hub or switch between the Modem and the Router

If steps 1-6 fail, then try this.  It worked for me.  

Why does this fix it ??  NIC cards and Hubs were built to be able to connect to thousadns of different vendor products.  Therefore, they allow signal levels that are out of spec - so long as the signals are readable.  But for some reason, some cable/DSL modems, and some home routers are built with very tight tolerances - they insist on signal levels within a specific, narrow range.  But as with all hardware - some Modems and some Routers will have voltages or signal levels that are out of spec. This causes the other device to fail, since it will only accept signals that are exactly within the legal range.

In the case where either the Modem or Router is just a tad beyond specs (or the signal to your home is out of spec !!) - a hub is more "forgiving" of poor signals, and it acts as a repeater  .  .  .  which regenerates/reshapes/amplifies the dignal - so if you insert one of these 'forgiving" hubs in between the two devices - problem solved !!!

The Hub's Uplink Port - the uplink port takes the leads from the LAN port next to it and reverses the two pairs of wires (transmit and receive), making it a DTE port. The last LAN port and the Uplink port are shared.  The LAN ports are DCE and are used to connect to DTE wired Ethernet interfaces, such as workstations.  The uplink port is used to talk to other DCE devices such as hubs, routers, or switches - without having to use a crossover cable. 

When connecting two hubs, only use the uplink port on one of them.  If you do connect two uplink ports together, as with any DTE-to-DTE connection, you will need a crossover cable.  Since the Uplink is nothing more than a reversal of the adjacent LAN port - you can hook any hubs, switches, or routers together whether or not uplink ports are present. Simply use one of the LAN ports instead, and connect them to another hub, or a router or switch, using a crossover cable.  

Many hubs have 4 or 8 LAN ports and 1 Uplink port.  If you do not use the Uplink port, then you can use all LAN ports.  But if you use the Uplink port . . . you cannot use the shared port that sits next to it.  It's taken.  The adjacent port is usually Port 4 with a 4-port hub, or Port 8 with an 8-port hub).

Crossover Cable - standard Ethernet cables are "straight-thru".  Pin 1 on one end connects to Pin 1 on the far end, Pin2 to Pin2, and so on.  There are only 4 pins that are used, since you only need two wires for transmit, and two for receive. The two pairs used ar 1-2, and 3-6.  With a crossover cable, the wires connected to Pins 1-2 on one end are "crossed over" and connected to Pins 3-6 on the far end.  The same is done with the wires connected to Pins 3-6 - they are crossed over and connected to Pins 1-2 on the far end.

The DCE and DTE Considerations

Be careful here - the modem, router, and hub are all DCE devices.  A standard patch cable is used for DCE-to-DTE.   For DCE-to-DCE or DTE-to-DTE you need a crossover cable (available at any computer store).

DCE Ports (connect to DTE ports with standard Ethernet cable)  -  Router LAN ports, Hub LAN ports

DTE Ports (connect to DCE ports with standard Ethernet cable) - Computer NIC port, Router WAN port, Hub Uplink Port

The following diagram shows normal connectivity, and the two methods of using a hub as a buffer between the modem and router - one with a 4-port hub with a 5th, Uplink port  -  and the other hub with no Uplink port, where a crossover cable is required.  This 3rd configuration was successful for my own case.

IMPORTANT:  after doing this - power down your devices, wait 30 secs, then power them up in this order:  Modem, Hub, Router, PC.  Then release and renew the IP address of your PC, and your Router.  Do this in DOS for your PC (winipcfg for Win98, and ipconfig /release, ipconfig /renew for WinXP).  For your router, follow the manual - it is normally done with your web browser, by entering to bring up config menus.


8)  Flash the Firmware

9)  Buy a new Router

Some routers are bad, and simply cannot obtain a DHCP assigned address from the Modem