Ipconfig /all will tell you who the current DHCP server is for an active lease. Use that to confirm ASB's earlier suggestion to make sure there's not a rogue DHCP server on the network.
I also second the questions about public IP's and addition DNS server requirements just for VPN/remote host resolution... -sc From: [email protected] [mailto:[email protected]] On Behalf Of Melvin Backus Sent: Thursday, April 24, 2014 8:27 AM To: [email protected] Subject: [NTSysADM] DNS server settings getting changed OK, this has been driving us nuts for a couple of days now. One of our remote sites is seeing seemingly random PCs change their DNS server settings. They're all configured to get them from the DHCP server, and it has the correct DNS servers. All the PCs do in fact get the correct settings when they get or renew an IP. That all seems to be working as we expect. But periodically we'll see a machine change the DNS servers to something else. This causes applications to start failing because the hosts they need no longer resolve. As soon as the PC renews it's IP, whether automatically or manually, everything goes back to normal and stuff works again. We have a short term fix (force the DNS server settings manually instead of DHCP) but that doesn't explain what's going on, and since we're using this same setup in 20 offices it also begs the question of why just this office. Background: Multiple small offices with either /28 or /27 networks. They are publicly routable IPs due to requirements for a partner VPN. The DHCP server is on the Juniper SSG FW. It servers two pools, one for PCs, another for phones. The PC subnet is publicly routable, the phone subnet is a non-routable 10.x subnet with matching ranges. (12.x.x.x/27 and 10.x.x.x/27). All DNS points to the home office. Until recently these pointed strictly to our domain DNS servers. As part of the VPN requirement we have set up a second set of DNS servers which are used to resolve hosts in the partner's domains. This is done with conditional forwarders. Partner DNS traffic gets resolved by their servers, everything else goes to our domain DNS or the Internet as required. This all works fine except in a single office. Even in that office it worked fine for weeks and has suddenly started this "revert" behavior. When the PCs change, they go back to pointing to our domain DNS which can't resolve the partner hosts. My question becomes (sorry it took so long) how do we track what is actually changing the DNS settings? I can tell when it happens fairly easily, but nothing in the event logs, etc., seems to indicate what triggered it, or what process is doing it. It doesn't happen as part of a DHCP operation as best we can tell. -------------------- Melvin Backus | Sr. Systems Analyst | Byers Engineering Company | 404.497.1565 Service Desk | 404-497-1599 | http://servicedesk.byers.com -- There are 10 kinds of people in the world... those who understand binary and those who don't.
