Random DNS Switch?

S

stim

n00b
Joined
Jul 17, 2010
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49
Hey guys,

Throughout the day today a few of my users have had their internet drop out from under them.

This is easily (but temporarily) fixed with a quick ipconfig /renew, but I am trying to see what we can do to stop this from occurring.

For some reason the NIC switches to some random DNS server (192.168.37.1).

We have a symmetrical 3MB internet connection going into a Sonicwall router and then into a Cisco 3560 switch for distribution to the workstations.

We have 1 other router on the network, but it has DHCP disabled so it just acts as a wireless hotspot.

We have made the following recent changes to our office:
- added 3 new computers to the switch
- changed priorities on the router for certain computers by MAC address
​

Let me know if you need any more info or have any ideas.
 
Static dns set or is it a dhcp recieved one? (when it changes)

Also anything else change? gateway, ip? subnet?
 
All computers are set to receive IP and DNS from the router, nothing is set on the specific computer.

Everything else stayed the same.

We actually use a bare IP address to access one of our servers offsite and this was still functioning, which makes me think that only the DNS address changed, making it so that the computer couldn't resolve plaintext URLs.
 
stray DHCP server.
I had that happen to me; only DNS changes.

Somebody downstairs had plugged a LAN port on a Linksys router into the network.

have you tried pinging the IP?
 
Hmm. one of my coworkers just found this http://windows.microsoft.com/en-US/windows7/Using-ICS-Internet-Connection-Sharing

I wonder if someone's computer is set up to try and use ICS.

I guess i will go through the newly added comps first to see if it is enabled once people leave for the day.

j-sta said:
stray DHCP server.
I had that happen to me; only DNS changes.

Somebody downstairs had plugged a LAN port on a Linksys router into the network.
Click to expand...

I will check the other router we have on the network, but it has been plugged in for a while before the problem started (today). No other physical cabling was changed during the addition of new machines either.

j-sta said:
have you tried pinging the IP?
Click to expand...

No response on that ip address.
 
the ICS is a possibility that very well could/would cause that; since ICS essentially turns a computer into a router which does DHCP.
 
ICS turns the "LAN" nic on the machine to 192.168.137.1 or 127.1 from what i've seen.
 
So I wake up to a call this morning that our internet is down.

It sounds like there is/was something f'ed up on XO's end.

The major issues we were having this morning seem to have abated, but we will see if the errant DNS pops up again over the next few days.

Thanks, guys!
 
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