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Very Weird DHCP Problem

Discussion in 'Networking, Telephony & Internet' started by x0nt, Jun 20, 2010.

  1. x0nt

    x0nt Member

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    I have a very very strange DHCP problem I can't work out.
    The problem is that my Macbook Pro cannot receive an IP from the billion DHCP server on my router.

    I have a Billion 7800N and various devices on the wired and wireless network (5 laptops, 2 desktops, 2 airport express's, 3+ iphones etc etc).
    Every device receives an IP fine, no problem, except for my Macbook Pro laptop, 15in 2007 model. Now, on the wired network, the laptop receives an ip fine, but the airport card can't. If I set the tcp/ip info manually everything is fine and life is good.

    So, I figured well, my airport card / mac-os must be stuffed. So I tested my airport card on many other networks. Lo and behold, dhcp works fine on the airport card. What you say??? Yes, works fine, no problem.

    So strangely, only when using my laptop and this 7800n device together, dhcp fails.

    This has been going on for some time, I can't remember when exactly but I've been trudging along fine manually configuring my IP, but it's come to the point that every time I take my laptop to another wifi network I have to turn on DHCP and vice versa when I return to my home network. It's annoying to say the least.

    I've updated my firmware to the latest 1.04c only yesterday and the problem still occurs.

    I thought I'd do a bit of a a look into what osx is doing so I set 'ipconfig setverbose 1' to spew the dhcp sequence into the system log. And the full packet trace of the dhcp sequence to the file "com.apple.IPConfiguration.bootp" found in /var/logs/.

    I'm no network engineer so I'm not sure exactly what is happening. But for those that can:
    I've hosted the com.apple.IPConfiguration.bootp log at http://files.me.com/johnwiles/hr5rqp
    and an exerp from the sys log concerning any dhcp events here: http://files.me.com/johnwiles/b3n72q

    Please have a look. Any help is much appreciated!
     
  2. ledhead900

    ledhead900 Member

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    This might seems dumb but have you checked how many Ip's you have set DHCP to dish out. I mean if you run all those devices at the same time It might not be an issue at all with the mac but more like the DHCP does not have an Ip for you. I'm not a engineer either but I would really would be looking into maybe the routers DHCP config and maybe the logs to see if it even sees the mac trying. tho I could be 1000% wrong
     
  3. SpudBoy

    SpudBoy Member

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    the authentication settings on your router are different to what the macbook uses during the negotiation process..


    This is quite common really.

    I have seen this myself on a system running ubuntu that wouldnt get a dhcp lease, but the same system worked under windows.

    (had to change the driver to set AuthMode=wpa as the router was wanting the adapter to authenticate before dhcp)
     
    Last edited: Jun 23, 2010
  4. ledhead900

    ledhead900 Member

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    I beg to differ I run ubuntu and I also have the SAME router as the thread start.

    Connects over wireless just fine, also I don't see how the negotiations would be different as that would be not following the standards there for not compliant. After all Standards are there for a reason to prevent this type of communication error.

    Tho I think I might be misinterpreting what your saying after reading it again u seem to think the Macbook is trying to authenticate a different way then what the routers authentication is setup to be if this is the case the User should check his Macbook Wireless settings in comparison to the Routers Wifi security page and set to appropriate method.
     
    Last edited: Jun 23, 2010
  5. SpudBoy

    SpudBoy Member

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    possibly - i did not word it very well.

    I had to tell my ralink driver to use AuthMode=wpa for it to connect correctly (If i used static IPs it worked without this setting).

    it looks to me like it is trying to gain a dhcp lease before it authenticates.
     
  6. ledhead900

    ledhead900 Member

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    Tho I don't know the process very well that it takes to authenticate you may be correct but that just brings me back to thinking that the device and the router are using different security settings. As i know that in windows sometimes you have to manually set what Method (wep,wpa,wpa2) before your try and authenticate or it will fail as it cannot automatically set its own method for what ever reason.

    But I dont think its connecting that is the issue here as the OP says he can connect to it just fine using Static ip. I still think that he might need to double check his security method used on his macbook as the airport card might work with his router but his macbook settings are not correctly set the same.

    It could be the other way around the airport card does not support what the router security method it is set on.
     
  7. SpudBoy

    SpudBoy Member

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    the issue i mentioned can happen even when you have wpa auth turned on with the router, and on the pc.

    the point i was making, that sometimes the router is expecting the pc to authenticate before dhcp is provided. - some drivers/software does not expect this and thats where the problem surfaces. - also hense why it works when a static ip is used, as dhcp isnt needed, the pc then authenticates as normal.
     
  8. ledhead900

    ledhead900 Member

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    well worded like that it makes sense to me now as well. Obviously if the software is expecting DHCP and the router is saying NO NO not until we verify your allowed to be on this network, The computer is just going to sit there dumb founded as like u explained it won't start to authenticate until it gets DHCP.

    We can't actually troubleshoot that if we can't see whats going on during the process so we are going to just have to try our best to eliminate everything else.

    If this is the case then I would almost say it was the Airport card but given the fact it connects just fine to other networks just proves that Macbook and the airport card are following the same standards used for networking hardware and something else specific to his network is the cause i'll have to do some research for this one I think.
     
    Last edited: Jun 24, 2010
  9. SpudBoy

    SpudBoy Member

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    yep, good to see you understand me know - sorry for the vagueness but it has been a while since i have had to modify anything.

    first up, lets see if we can find out what chipset this airport card has.

    1. recent mac airport cards have either used an artheros chipset or a broadcom one.

    i know the artheros ones did require a little low level tweaking (at least with ubuntu) to work with some non-apple accesspoints. (like changing authentication to include dhcp negotiation).
     
  10. swipe

    swipe (Banned or Deleted)

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    Can you set an all lower case 8 letter DHCP Client ID and then post the bootp log of the session if it fails?
     
  11. gdjacobs

    gdjacobs Member

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    WPA operates at Layer 2. It must be negotiated before the DHCP handshake will succeed. If you can manually set the IP address, WPA is not a problem.

    The syslog doesn't say much except that DHCP is timing out. The bootp log tells a more detailed story.

    The first sequence consists of a DHCP Discover message from your Mac which is answered by the DHCP server in the form of a DHCP Offer (IP address 192.168.1.1). The Mac requests the offered IP address, then the router does not grant the address to the Mac. Sometimes it tries the request a few more times, before recycling back to a Discover message.

    This looks normal from the computer end, but it seems the router is conflicting. The way the router works, it should create a table of reserved IP addresses (those given out already which haven't expired, plus any that you've manually programmed into the router). When a computer tries to connect, the router will look at the range of IP addresses it's supposed to work with, exclude any in the table, then offer an unused address to the computer (usually the next one in numerical succession). If the computer is manually allocated in the router or has previously been connected to the network, the router can provide the appropriate IP from the table. This part works, because the router is making an offer (not sure if the IP makes sense). However, when the computer makes it's DHCP request, the router finds the address is either not in a valid range, or already taken, or something from left field.

    Missing information: I don't know if that address is already assigned to another device., either statically or dynamically. Audit your other devices to see. I don't know if that address is in your routers offer range. That should be listed in your router settings. I don't know if there are manually allocated IPs on the router. Again, check your router settings.

    Curious, what IP do you assign statically? What IP does the built in ethernet get?

    Who provided the router? Your ISP?
     
    Last edited: Jun 24, 2010
  12. swipe

    swipe (Banned or Deleted)

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    Don't forget to include any virtual interfaces (from VMWare Fusion, Parallels, or similar) in your audit.
     
  13. OP
    OP
    x0nt

    x0nt Member

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    Thanks for your help guys, just for reference, the Airport card is an Atheros 5416.

    I had not set the DHCP client ID.

    The DHCP server in question is the only one on the network, that is definite. The range selected was 192.168.1.1 - > 192.168.1.20, with less than 20 devices and the period selected 24hrs, this should not be a problem.

    The address offered 192.168.1.1 was not in use, well in fact, the address was supplied from the router as specified in the 'offer' packet. So the address must have been available from the routers pool.

    Built in ethernet gets the same 192.168.1.1 address offered, however this can change depending on other devices and how long this computers been 'off' the network.

    Statically I assigned an address not in the routers pool (.54), I purchased the router, isp is netspace.

    However, this is all now a bit of water under the bridge because I've solved the problem luckily!
    I re-flashed the device and set all settings back to factory-default. I re-input all my settings and everything seems to run ok.
    I'm going to guess there was an error with the settings somewhere causing this problem.

    Phew! Can't believe the hassle it took me to diagnose the problem, in the end it only took half an hour to re-input all my settings after a factory reset and firmware flash.

    :)
     
  14. Falls

    Falls Member

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    So the root cause of your issue is your didn't perform a factory reset of the 7800n before your flashed to firmware 1.04c?

    F.
     
  15. OP
    OP
    x0nt

    x0nt Member

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    No, the issue was around before 1.04c.
    I've upgraded the firmware 5 or 6 times, all completed perfect and never did a factory reset.

    The issue came about during normal operation and not subsequently after a firmware upgrade.

    I'm not sure what the root cause of the problem is was.
     
    Last edited: Jun 30, 2010
  16. Pieter...

    Pieter... Member

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    I had a DHCP failure with my 7800N 1.04c to after 20 Days up-time, I've sent the logs through to Billion to Analise.
     

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