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  1. #1

    Questions on GRUB and ethernet modems

    I have 3 questions to ask about GRUB and adsl ethernet modems. Here goes:

    1) Do you know the steps to reinstall GRUB, in case the OS bootup screen disappears. (e.g when windows is reinstalled) ?

    2) I want to buy an ethernet adsl modem. What models are compatible with linux ?

    3) Presently I have a LAN connecting 2 pcs at home. The IP addresses and subnet masks are manually configured. Hence, if i install the adsl ethernet modem on 1 pc, do I have to change the NIC to use DHCP or can i continue using my manual IP and subnet settings?
    My friend,whose linux connection works, told me to keep the manual settings while a linux book I read said most adsl connections use DHCP.

    Please reply quickly if you can. Thanks!

  2. #2
    Linux Engineer
    Join Date
    Nov 2002
    Queens, NY
    !) GRUB can be reinstalled to the MBR. In my case, I have one IDE hard drive and the MBR obviously in there. I run 'grub install /dev/hda' and that puts GRUB back into the MBR.

    2) I don't know how DSL works but I would think that they give you an external modem. Once you have that, you'll need an internal NIC card that plugs into the external modem. Most brands work well with linux. It's other things like printer and scanner drivers that are harder to find.

    3) Again, I don't know how DSL works but my cable modem gives one IP address. I have a router that does NAT. It can act as a DHCP server but I choose to manually configure my IP address for port forwarding reasons. So computer A and computer B both acccess the internet through the router which in turn goes through the cable modem.
    The best things in life are free.

  3. #3
    Linux Guru
    Join Date
    Oct 2001
    Täby, Sweden
    1. Alternative method: GRUB can install itself on the MBR by using the setup or install internal commands. Use the help internal command to get information about them. You can set up a GRUB boot disk using the GRUB image and rawrite.exe from my homepage. The GRUB stage 2 file is required to be on the hard drive, though.

    2. If you get such a modem that bpark was talking about, there's no problem. Many companies deal with USB modems, though, and they're a _lot_ trickier. There are very well supported drivers for some, while others aren't supported in Linux at all. Check with the dealer before you buy it.

    3. If you get one of those modems with an ethernet connection, I would suggest installing two NICs in the computer you will be using it on: one for the modem and one to connect to the other PC. That way you can also make the box with the modem connected to a router. That way the other system can use the internet via the first one. The NIC connected to the modem will run on DHCP (or static, if that's what your ISP wants, which it usually isn't) while you can configure the other one as you wish.
    If your modem is connected via USB, it will automatically get a network interface on its own, and the same principles are valid, except that you don't need another physical NIC.

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  5. #4

    Few more questions about grub and ethernet adsl

    Hi Dolda2000 and bpark,
    Thanks for the advice you have given. I have a few points to confirm though.

    Is 'grub install /dev/hda' a command to be typed on the command line?
    What is the grub stage 2 file and where to I get it?

    Lastly,what does NAT mean and is the router the only device to have NAT? Do ethernet adsl modems have NAT too?

  6. #5
    Linux Guru
    Join Date
    Oct 2001
    Täby, Sweden
    There is a small typo in bpark's post. It should be "grub-install /dev/hda", not "grub install /dev/hda", but, yes, it is a shell command.

    Since the boot sector on IBM compatibles (ie. PCs) only is 512 bytes long, and GRUB is much larger than that, GRUB is divided into two stages. Stage 1 fits into the boot sector, and its only job is to load stage 2. Stage 2 resides in a file that probably already is somewhere in your /boot directory, by the name stage2. If it isn't there, you will be able to find it in /usr/share/grub/i386-pc.

    NAT stands for Network Address Translation, and refers to the process of letting several computers connect to a network (eg. the internet) through one node on that network by letting that node translate all packets forwarded onto the other network making them look as if they came only from itself.
    Hardware routers are certainly not the only devices that support NAT. Linux supports it as well, and is much better at it as well. Yes, it's harder to configure Linux to use NAT than letting a hardware router do the job, but it's often much cheaper, since you don't have to buy a hardware router.
    Ethernet ADSL Modems do not support NAT, on the other hand. A Modem is, just like the name suggests, just a MOdulator/DEModulator, which means that all it does is modulate the signals to enable them to travel over phone lines. Some are a bit more advanced than that, but I haven't heard of models doing NAT.

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