Situation: 20 computers in the same windows workgroup. They are connected with some switches. Then there is router and a firewall (2 separate hardware, but I don't know how they are connected) with the physical ADSL modem to the internet.
Computers have mostly windows XP, some windows 7. In the TCP/IP configuration of each computer, there is a fixed IP address, and the gateway is the router's IP. The DNS are those of the ISP, or the IP address of the router. In the router configuration (via http), I saw a page where DNS was set to "from ISP".
Suddendly happened a problem: when browsing websites, some computers begun to receive a official ISP page that says "you have problems with DNS, we suggest you to use automatic DNS". Other services stopped working (banking, and things that needed to resove addresses for communications)
I phoned to the ISP and they told me they were having problems with DNS.
So I thought: if I change DNS on my computer TCP/IP config (say openDNS for example), than I will use those DNS and bypass the ISP broken DNS. BUT the problem was still there. No matter how I set DNS, I still receive ISP error webpage. I also tried to change the firewall DNS (from "from ISP" to openDNS), no success.
So another guy (sort of 50 years old Linux fanboy) claimed that "Linux does not have problems, and the DNS I set here will be used, it does not depend from ISP". Apart from trolling.... I asked him "so why I still receive ISP error page, if I use different DNS?"
So now, I would like to understand what happened.
I restarted PC, I "ipconfig /flushdns", and empty all browser's data, so to start fresh.
I kindly ask the community these:
- Assuming no other NAT/rules exists, if my PC ha open DNS, and the router has ISP DNS, who wins?
- Is it true that with a port forwarding rule (all traffic to port 53 --> force go to DNS of my choice) I am able to force the use of my DNS of choice for the entire LAN, even if client PC have specified a different DNS?