[Dnsmasq-discuss] How to troubleshoot NXDOMAIN for local devices?

Todd A taa at pobox.com
Fri Feb 16 17:03:02 GMT 2018


On Thu, Feb 15, 2018 at 2:46 PM, Andy Ruddock 
<andy.ruddock at rainydayz.org <mailto:andy.ruddock at rainydayz.org>> wrote:

    Todd Andrews wrote:
     > Hi All,
     >
     > I'm running dnsmasq 2.76 on a Raspberry Pi. It's been working
    great for
     > months but today I started seeing an odd behavior for a specific
    local
     > device and I don't know how to troubleshoot it.
     >
     > The device is a Dell Inspiron 5577 Windows 10 Home edition laptop
    with the
     > latest Windows updates. It's getting an IP address of
    192.168.1.115. I
     > first noticed the problem when I tried to establish a VNC
    connection to it
     > because I can't connect via its hostname, "sagan", but I can
    connect via
     > its IP address.
     >
     > Neither the IP assignment nor the laptop's MAC address appear in
     > dnsmasq.leases. The only reason I know it is assigned .115 is by
    physically
     > going to the laptop and running the Windows 'ipconfig' program at the
     > command prompt.
     >
     > I've rebooted the Raspberry Pi and the Windows 10 laptop, but it
    hasn't
     > made a difference.
     >
     > More info below. Does anyone have any ideas?
     >
     > Regards,
     > Todd

Hi Andy, thanks for getting back to me so quickly. (I originally sent 
this reply yesterday but forgot there's a maximum size per post to this 
list. Replaced screen capture with a link below.)


    Are you sure the windows box hasn't been configured with a static IP
    address?


I'm positive: click to view screen capture 
<https://www.dropbox.com/s/cwy72yu4sly62mp/sagan-configured-as-dhcp.PNG?dl=0>

    Any information when you refresh the IP address from within a cmd window
    in Windows?
             ipconfig /renew


I never would have thought to try this. It gave a strange error but 
renewing fixed the problem immediately. Here's the error:

    C:\Users\taa>ipconfig /renew

    Windows IP Configuration

    An error occurred while renewing interface Ethernet : The name
    specified in the network control block (NCB) is in use on a remote
    adapter.
    The NCB is the data.

    C:\Users\taa>


Having a specific error allowed me to Google it and find Bizarre DHCP 
server error solved 
<https://web.archive.org/web/20161126203756/http://www.formortals.com/bizarre-dhcp-server-error-solved/>. 
The poster at that link 1) was not getting an IP address at all, 2) was 
running a Windows DHCP server, and 3) "found a second reservation in 
DHCP which looked odd; it had the same IP address as the first one that 
we deleted but it had an entirely different MAC and name."

This made me remember that a couple of weeks ago I changed my laptop's 
Computer Name in Windows.

Does this mean there is some other place where dnsmasq might have cached 
the IP address or MAC or hostname? I'm trying to figure out 
why dnsmasq.leases had no reference to the laptop's IP/MAC/hostname, 
neither the previous hostname or the new one. Maybe this is one of those 
cases that is so bizarre it defies explanation (and I can live with 
that). :D
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