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Network Problem

  1. Nov 13, 2005 #1
    I have a small problem with my lan. The setup is as followed:
    The cable modem is connect to a hub, which is connected with my own pc. I used to have an older machine [win2k, normal network card] which had no problems connecting to the network and to the modem. About one week ago I got myself a new pc[winxp pro, gigabite extrem network card from broadcom] which can no longer access the network. The tcp/ip config is the same. The only difference is that I no longer receive data.
    Now my question: What should I try? Is there maybe a problem with the lan card?
    thanks for your help
  2. jcsd
  3. Nov 13, 2005 #2
    I would eliminate the hub first and try connecting that way.
  4. Nov 13, 2005 #3
    What for? I know that the modem works since another computer is connected to the hub [win2k] which has access to the internet. I did try to connect using this computers rj45 cable but it still didn't work.
  5. Nov 13, 2005 #4


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    Science Advisor

    Could you post the tcp/ip settings for both computers here? Are you specifying a DNS server? Are you using a static ip? Since you have a hub instead of a router you may have to specify these settings.
  6. Nov 14, 2005 #5


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    Staff: Mentor

    Is that a hub or a router? Also, have you run XP's network setup wizard? I've had problems setting up networks manually in XP - it doesn't seem to want to allow it.
  7. Nov 14, 2005 #6
    It is a hub and yes I have tried to run the xp config which didn't work as well. Both computers have the same settings. Everything is set to dynamic. No, no fixed ips or dns.
  8. Nov 14, 2005 #7
    Do you have the windows firewall enabled? Or any other firewall?

    Confirm both PCs are in the same workgroup also.
  9. Nov 14, 2005 #8


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    You say that you had it working in this configuration previously,

    2 computers -> hub -> cable modem

    It is not clear to me how it could work. My cable modem wants to talk to a specific MAC address, it will not work with 2 computers on a hub. You need a router which has the MAC address for the cable modem, it then delivers information to the computer which requests it.

    Generally the configuration for 2 computers, or more, and no router; is to have a second LAN card in one of the machines. The extra LAN card is connected to the cable modem and ICS is used to control the information flow through the other LAN card to the network.

    It seems to me that the cable modem has the MAC address of the 2nd computer and is quite happy talking to it alone. I do not know if you can you make ICS work in the configuration you have.
  10. Nov 14, 2005 #9
    You are correct.

    He said he couldn't access his network which I was thinking are his two pcs.

    I was under the impression he could not access his other computer.

    He really didn't clearly state the problem.

    ICS will not work with the Internet connection running off of the hub. To use ICS you need one NIC for the Internet connection and another NIC to run to the network. ICS is actually kind of like a cheap NAT service.

    Blackjack... you can either buy a router or buy a cheap NIC.

    If you just want to go cheap, buy one network card and run a standard cat5 to your hub. Then plug the cable modem into your extra NIC and setup ICS. It works the same as a router essentially.
    Last edited: Nov 14, 2005
  11. Nov 15, 2005 #10
    So if I have understood you correctly : My cablemodem has memorized the mac address of my old computer and won't let me access the connection because my new mac address doesn't correspond with the old one?

    [no. no firewalls. What I thought I knew was, that a hub just shares the packets and doesn't bother about anything (which worked fine with the old computer).]
  12. Nov 15, 2005 #11
    Yes your cable modem will only take one MAC address. It has one interface and expects to end on a NIC.

    If you unplug your old pc from the hub and reset your modem it will probably lock onto the MAC of your new computer.

    A router (at least a home use one) typically has a switch in it as well. A switch is just like a hub except there aren't collisions like there are on a hub. A hub kind of broadcasts information to every connection on the hub. A switch actually only sends the information to the correct port.

    A home use router has an internet port and then several switching ports. The router takes that single interface and uses NAT or Network Address Translation to allow traffic from each of the switching ports. NAT is like an intermediate interpreter. It assigns a port or range of ports to each connection on the switch. So when data comes in and out of the router it can interpret where the data goes.

    This is why NAT is somewhat secure. If someone does a portscan on your router it will not reveal the open ports on your PC. It will only reveal the ports on the router. If the router has assigned its port 1233 to your PC then to penetrate NAT you have to know the destination computer is behind that port.

    This is also why you have to enable port forwarding for web services such as a web server. You have to tell the router to make its port 80, port 80 on a specific PC. Then when incoming requests come in to the router it has a static rule to direct traffic.
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