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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?"
If the small local ISP is screwing up, and refuses to respond in any useful way despite your best repeated efforts, it sounds like its time to take your business elsewhere, maybe to one of those large ISPs you mentioned. And make sure you tell them WHY. Who know, maybe the threat alone will be enough to get them to make a sudden change in policy for you, with a month or two of free service to boot.
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?
to force use of internal DNS servers while connected.
Done.
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!
http://en.wikipedia.org/wiki/Split-horizon_DNS
What's the benefit of blocking your internal DNS? You're firewalled off, or they wouldn't need the VPN. What's going on here is that you're doing something broken - you must have some kind of NXDOMAIN redirector running on the remote machine, and the ISP is doing something wrong, because its NXDOMAIN redirector is fooling your NXDOMAIN redirector. If you just follow the standards, the fact that they have a broken NXDOMAIN redirector wouldn't affect you.
Another option is to set up a DNS resolver that's reachable from outside your network, and also inside your network, but only answers for your internal names if the query comes from inside. Then configure all your VPN machines to always use that nameserver, and not use your ISP's nameserver.
Even if your ISP filters DNS and answers in place of your nameserver, you're okay, because as soon as the VPN is set up, all the queries will go across the VPN (since this server is on your local network). At that point you'll start getting answers for local domains because now the query is coming from a local (VPN) IP address.
This second solution is a bit more work, and of course being a DNS geek I'm biased toward just doing the right thing in the first place, so I recommend just opening up your DNS, but either way ought to work.
There are still small ISPs left where you live?
Mod parents up, please.
And then we can all go home. This is an easy problem to solve once you see it from the right angle, and that angle is described above.
Kid-proof tablet..
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.
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.