ISP DHCP client requirements
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Thread: ISP DHCP client requirements

  1. #1
    Junior Member
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    ISP DHCP client requirements

    I hope I'm putting this in the right forum. I'm not sure if a BSD is considered similar enough to linux or not. Anyway...

    I'm having a problem getting a DHCP server to give my OpenBSD box an IP address.

    When I took apart the DHCP discover packets between my OpenBSD machine and a random Windows machine, the difference was that the discover packet on my OpenBSD machine wasn't sending any client identifiers. My windows machine sent a hardware type of ethernet and my network card's MAC address. I've been looking through man pages, and I can't find the syntax to add that information to my dhclient.conf file.

    Any help would be appreciated.
    ~Aracor

  2. #2
    Senior Member
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    Let's see your syslog files. If your DHCP client can't get an IP it will throw an error that will show up in the logs. What version of OpenBSD? What DHCP client? Generally, the quality of the answer reflects the quality of the question. BE SPECIFIC OR YOU'LL GET NO ANSWERS.

    And by the way, OpenBSD is Unix so this is the right forum for this post. Technically Linux is not Unix but that's another arguement.
    OpenBSD - The proactively secure operating system.

  3. #3
    Junior Member
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    Well, I'm running OpenBSD 3.2, and it's nearly a default install as of yet. The DHCP client I'm using is simply dhclient.

    I didn't think that based on the nature of my question the errors mattered, but I'm getting two of them commonly.

    dhclient: send_packet: Network is down
    and
    DHPACK from <DHCP server's address> rejected due to a bogus yiaddr of 0.0.0.0

    When I took apart the DHCP discover packets, the only major difference between the ones accepted and the ones not accepted by their server was that the packs accepted was simple.

    The accepted ones included Option 61: Client identifier
    Hardware type: Ethernet
    Client hardware address: <MAC address of network card>

    If there's anything else that may be needed, let me know. Like I said, I think all I need to do is find the syntax for adding my client identifiers into the dhclient.conf file. As an added note, I don't understand why it would be saying that the network is down because TCPDUMP is still seeing all kinds of packets flying around the network.

    Hope this helps
    ~Aracor

  4. #4
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    Well, I got it. And I was right, the version didn't really matter much. But just for the sake of completeness, and in case someone else has the same problem, I needed to add:

    send-client-identifier 1:<mac address>;

    to the dhclient.conf file. That sent the MAC address of my card to the DHCP server so they would return an IP address.

    Thanks anyway
    ~Aracor

  5. #5
    AO Security for Non-Geeks tonybradley's Avatar
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    I know this is already a closed issue and that you solved the problem yourself already, but I wanted to add my $.02 for clarification.

    I would have pointed you to the MAC Address portion as well. I have a broadband ISP (cable modem) which allows me a total of three IP addresses. They are assigned dynamically through DHCP, but I could have 3 separate devices connected directly with my ISP.

    When the cable modem was installed we had used my laptop to initiate everything by connecting it directly to the cable modem. After that I connected all of my computers through my router.

    A few weeks ago I decided to put a couple of computers outside of the router. I figured the router would take one IP address and my other 2 machines would each take one and that would give me 3 IP addresses.

    I got one computer online with no problem, but the other would not get an IP address from the DHCP server. Even after I disconnected the other computer I still couldn't get another IP address. But, when I connected that computer back up it had no problem getting an IP address again- only computer #3 couldn't get one.

    When I called my ISP to find out what was going on they said it was because their system doesn't track simply based on how many IP addresses my account has live at that moment. It logs the MAC Address. Because I had used my laptop for the original connection and then the router and then one of my computers, by the time I connected what I thought was the 3rd device, the ISP saw it as the 4th MAC Address and rejected it.

    By calling support I got them to clear the unused MAC Addresses from the system to free them up for use again. So, long story short (or not so short), if your ISP is like my ISP they require a unique MAC Address before they will assign an IP through their DHCP server.

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