Re: [LUG] wrong DNS allocation on client

Mon, 08 Feb 2010 06:28:49 -0800

Run ipconfig /all on the client machine (with administrator privileges). It will show the dhcp-server IP (entry) which supplied the client with the IP settings. That should indicate the rogue dhcp server (hopefully).

Regards,
Rocco

On 2010-02-08 17:19, Emmanuel Sekyewa wrote:
Mike, the DHCP server is running on Windows server 2003, will tcpdump still apply in this case? I also changed the scope with reference to the new addressing scheme.
Dan, it's a windows domain :-(
There are a number of unmanaged switches on the network, if at all there is any possibility that one of them could be supplying client machines with a wrong entry, before the DHCP server does, how is it that this only started happening after changing the addressing scheme?
 


On 8 February 2010 16:38, Mike Barnard <[email protected]> wrote:
On Mon, Feb 8, 2010 at 3:36 PM, Emmanuel Sekyewa <[email protected]> wrote:
> Good afternoon,
>
> I'm in a situation in which after changing the IP addressing scheme on a
> network, certain machines obtain a wrong entry for DNS at startup, but when
> I run an ipconfig /release and subsequently /renew, they pick up the correct
> settings/configuration for the DNS server. I have gone through my DHCP
> configuration a number of times to ensure that the correct IP addresses are
> specified for the primary and secondary DNS servers, but this still keeps
> coming up.
> This even happens after flushing the DNS cache on a client machine and
> rebooting.
> Any ideas of what could be causing this? Or a viable work around?
>

1 -- what platform are you running you DHCP server?
2 -- The quickest way to check whether you have another DHCP server on
the LAN is to run tcpdump and listen out for any bootp traffic. A
quick run of tcpdump -i <interface> -n port 67 or port 68 will show
you all bootp traffic on your LAN.
3 -- If you did not change the scope on your DHCP server, you may end
up with some wrong info.



--
Mike

Of course, you might discount this possibility, but remember that one in
a million chances happen 99% of the time.
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--
Emmanuel C. Sekyewa

+256 782 199 202

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