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Dealing With ISPs That Use NXDomain Redirection?
Vrtigo1 writes "I work for a small company that has about 50 staff on the road relying on VPN back to our office at any given time. Many ISPs have implemented NXDomain redirection services that hijack DNS traffic to show you sponsored links and other related ads when you mistype a domain name. These services are incompatible with most VPN software, since they prevent the computer from resolving internal hostnames. Large ISPs typically provide an opt-out on their sponsored links page that immediately opts you out of the DNS redirection, but I've noticed that some smaller ISPs and CLECs have opt-out links that don't actually appear to do anything. I don't have a good solution for employees using these ISPs, and our employees are getting frustrated because the problem is becoming more prevalent and we can't fix it for them. I've tried calling a few of these smaller ISPs for help, but it's been like talking to a wall. Manually changing DNS servers works temporarily, but the user can't resolve internal hostnames when they connect to the office LAN again. Have you had to deal with ISPs using non-standard DNS servers? What is your solution?"
Last time I setup a VPN, was with a Cisco PIX firewall, (its been awhile) but there was a spot to specify which DNS servers to use when connected to the VPN. I had specified that when connected, they would use our DNS, since they otherwise couldn't resolve \\file-server\share or whatever..
What are we going to do tonight Brain?
If you're splitting your connection between a VPN tunnel and a non-VPN protected internet connection, you're a security risk to your infrastructure.
Have your administrator configure full tunnel support where ALL of your traffic goes through the encrypted tunnel. That solves a security problem AND it fixes your DNS problem because you don't use your local internet provider's DNS servers.
Check out my sysadmin blog!
This guy sounds like a manager or IT worker who is having problems with his employees connecting to the work VPN.
it sounds more like he has not stated the problem correctly.
how is it possible that a VPN connection is doing DNS to an external name server? Should not every internet request flow over the vpn from the client to the server. once it reaches the internal vpn server the server should know how to route the internal addresses and for external addresses it could use an external domain name server. the problem described seems like it should not exist. what am I missing?
Some drink at the fountain of knowledge. Others just gargle.
Either way, what I do when I have some kind of weird situation where a user needs to change their TCP/IP config routinely is just put a couple shortcuts with pretty icons on their desktop that point to batch scripts that run a netsh script. You should be able to completely change an IP configuration on a Windows box with this utility, the user just runs "home.bat" when they're home and then "office.bat" when in the office. A Google for "netsh exec" should give enough info to get started.
This is in fact why NXDomain breaks things in the way the poster describes, however, unless you're the kind of employer who wants to see EVERYTHING your subordinates are doing it's not actually the best practice to filter everything through the VPN.
Filtering everything through their VPN increases overall costs in bandwidth and hardware as Intron indicated. These are very real, very costly expenses that many employers overlook when implementing broad policies... and it's a fantastic point you raised that all too many companies forget.
Why should my connection to slashdot.org, for example, be secure on the company VPN? My ssh and nfs connections have very real reasons to be secure however!! On the other hand you could fix this by filtering DNS traffic through the VPN, but not web traffic. The cost of DNS traffic is marginal comparatively to other services, but the benefit for companies facing these specific issues is obvious.