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Why does "ipconfig /all" on my laptop not display a DHCP Server?

Posted on 2008-10-01
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Last Modified: 2010-04-21
My little home network consists of a Desktop PC, a Laptop, a Netgear DS106 hub (not a switch or a router - just a hub) and a broadband cable modem. The computers both run Windows XP Professional.
My PC's motherboard used to have 2 LAN ports - one connected to the hub, the other connected to the cable modem. The laptop was connected to the hub. This configuration allowed the computers to see each other and for both to access the internet simultaneously (the laptop presumably going through the PC).

My PC has just come back from the repair shop with an "upgraded" motherboard that only has a single LAN port. I have therefore had to connect the PC, laptop and cable modem all into the hub. The problem now is that the compters don't see each other and only one can ever access the internet - the first one to be switched on.

When I use the "ipconfig /all" command on the PC, I am shown an IP address, a DHCP Server address and 3 DNS Servers. "ipconfig /all" on my laptop only shows an IP Address but no DHCP or DHS server addresses.

When I try keying in the same DNS address into my laptop's TCP/IP settings, they appear when "ipconfig /all" is run, but still no mention of a DHCP server.

Why does my laptop not see a DHCP Server address?
Where is the "DHCP server" in this simple network - my desktop PC, my cable modem, or my hub?
Is this simple "hub" connection capable of providing shared internet access or do I need to replace my simple "hub" with a "router", or get a second LAN card for my PC and try to go back to my original configuration? (I'm currently debating this with my repair shop but getting nowhere fast).

Any advice gratefully received.
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Question by:colinasad
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by:MikeKane
MikeKane earned 75 total points
ID: 22618391
The hub can not provide the shared access you describe.    

You would need a home router like a D-link or linksys (not recommendations, just options).  

My guess: Before, your PC was probably set to share the internet connection.    Your laptop connected to the PC through the hub, the PC handled the DHCP and took care of shared internet.  

If your original MB had dual Lan, the store should have replaced it with Dual Lan - If they gave you a new board, make sure you didn't get taken with a cheap replacement....  

A home router would set you back maybe $60 and up....  

You could add a 2nd nic to the PC to go back to your shared internet setup for less than that....  




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by:Darr247
Darr247 earned 175 total points
ID: 22619053
> The hub can not provide the shared access you describe.  

That's not necessarily so. It depends on what type of modem is providing the internet connection. I have seen modems that would provide addresses for and share the connection (using NAT) with up to 25 computers if it was connected to a switch.

Hopefully what you actually have is a switch, and not a ''hub'' as you called it, colinasad.

As far as what used to be happening, it sounds like windows' Internet Connection Sharing was providing DHCP before the repair (ICS addressing would make the gateway and DHCP server 192.168.0.1 for everything connected to the switch).

Anyway, before you buy anything, if you can tell us what brand and model the modem is (also the hub/switch) you might be able to make it work with what you have already.
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Author Comment

by:colinasad
ID: 22619413
Thanks guys,

As I said in my original posting, my hub is just that - a hub.
It is a Netgear DS106 6-port Dual Speed Hub. It does not mention "switch" or "router".
My cable modem is a Scientific Atlanta WebStar DPX100 Series Cable Modem.

I have no idea what the "ipconfig /all" results were before my motherboard change. Everything worked and I never needed to look.

Thanks for your interest. Colin.
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Darr247 earned 175 total points
ID: 22620124
According to the FAQ on page 18 of the scant documentation available for that modem (http://www.scientificatlanta.com/products/consumers/userguidepdfs/webstar_userguides/749610.pdf), it will support up to 31 devices., but does not give any specific instructions on how to do so.

I suggest setting all the computers to 'obtain address automatically', and connecting them all to the hub, using the ports 1 through 5 first.

Then connect the modem to port 6 on the hub, and set the hub's uplink switch to 'uplink' rather than 'normal'.

Shut down the computers and power off the modem (unplug the power adapter from the back of it, or its 'wall wart' adapter from the mains outlet). Wait a minute or so... power the modem back up and wait for its lights to come back on and settle down (usually takes a minute or so), then turn on the computers one by one and see if they are assigned addresses properly.  If not, change the uplink switch to 'normal' and do the shut down/power off sequence again and see if it works.

If that doesn't get it working, you may need to call your cable company's support department and ask how (which is what the modem manual's FAQ says to do). If they say it won't work and try to sell you a router, point out to them what it says in the manual on page 18. Now, if they want to GIVE you a router, that's a different story. ;-)

The disadvantage of using a hub is it divides up the 100Mbps bandwidth (that your network cards are probably all capable of) among all devices active on the network, while a switch provides 100Mbps of bandwidth to each port.  If not more than 2 devices are transferring files between them at any one time, it's not really a disadvantage... or if you're only using it to share the internet connection, that connection would need to be pretty fast for a hub to slow things down. I don't know of any manufacturers that have even made hubs in a few years, so you've probably had that for quite a while (or probably got a very good deal on it).  :-)
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by:kdearing
kdearing earned 100 total points
ID: 22620324
I wonder if the cable modem is in 'bridge' mode.
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by:Fred Marshall
Fred Marshall earned 150 total points
ID: 22620450
The disadvantage of using a hub is that it MAY divide up the 100Mbps bandwidth.

A switch won't help you if all the computers are trying to access the same port - e.g. the port providing the internet connection.  It will help you if you have 4 computers and most communication is between  pairs of them.

Darr247 gave good advice.  Either the modem will give you more than one address or it won't.  
A pretty good clue is this:
What is the address given the one computer?
Is it a public IP address or a private IP address?

If it's public then you're probably stuck with needing a router or a computer as router - either with DHCP.  This would likely be the case if the modem is in bridge mode.

If it's private then it's also likely that you can get more than one address out of it as described in the manual.
Private addresses most common:
192.168.1.x
192.168.0.x
10.0.0.x
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Author Comment

by:colinasad
ID: 22622003
Thanks for all your help folks, I appreciate the time you are taking over this.
Yes my hub is an "old" one - more than 5 years at least I think.
Also, I have had my cable modem for more than 4 years.

When both computers are configured for "Automatic" IP Address assiging, the "successful" computer (Iie the first one switched on after (yet another) full shutdown and switch off, gets the following :
IP Address : 77.99.104.1
Subnet Mask : 255.255.255.0
Default Gateway : 77.99.104.1
DHCP Server : 62.31.64.115
DNS Servers : 62.31.64.39
                        62.31.112.39
                        62.31.144.39
(The IP Address has also been 77.99.105.4, with a gateway of 77.99.105.1, but always with a "77,99" prefix)

The "unsuccessful" (second switched on) computer gets given the following sort of addresses
IP Address : 169.254.246.101
Subnet Mask : 255.255.0.0
Default Gateway : 169.254.246.101
with no mention of "DHCP" or "DNS" servers in response to "ipconfig /all".
The "unsuccessful" computer also tends to have "Limited or no connectivity" on the LAN network connection.

I do have my modem connected to port 6 on my hub. Although that socket is not labelled as a "WAN" socket. It does have a "Normal/Upload" button and I have tried both settings (powering down everything between attempts), but always with the same results.

I will pursue Darr247's line about the functionality of my modem. In the meantime, any other suggestions?

Many thanks. Colin.
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by:kdearing
kdearing earned 100 total points
ID: 22623418
OK, you're getting a public IP address; not good.
That means your modem is in bridge mode.

You've got 2 choices:
1.  If the modem is capable of it, put it in 'gateway' mode; this turns on router functions and NAT
2.  Get yourself a router and connect the WAN interfact to the modem.
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by:Fred Marshall
Fred Marshall earned 150 total points
ID: 22625728
To elaborate:
The address you're getting is a public address - connects you straight into the internet.  So, make sure you have a firewall running!

The other address starting with 169 is an APIPA address - a private address that is set by default internally when the computer can't get an address any other way.  OK only in very limited circumstances and surely not for a real LAN.

Routers can be had for as little perhaps $19.95 and certainly are available for $24.99 recertified or $30 to $35.  There is the D-Link EBR-2310 available at around $35. Personally I'd go for a WRT54G or BEFSR41 for a bit more money.    Going this way gives you more flexibility without much trouble in setup and avoids digging into the PC hardware or software.
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Author Closing Comment

by:colinasad
ID: 31502819
Thank you all for your time and advice. Although I didn't fully understand the deeper technical points I know I needs a second NIC in my PC or a new router.
I have tried to split the points fairly but know some must look a bit paltry, but I think the A rating means they will be multiplied up.
Thanks again.
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