Hostnames Fail to Resolve over VPN

Question

We provide our employees with L2TP VPN access so that they can securely connect and access corporate resources from their personal computers at home. For the last few months we have been battling an issue where the personal Macs owned by various employees suddenly stop resolving hostnames over the L2TP VPN tunnel (their personal Macs initially work fine on the VPN, but after months of use they suddenly stop resolving hostnames).
If I try to ping the hostname/FQDN of a resource across the L2TP VPN tunnel (i.e. "dev01.corporate.ad"), I get an error stating:
ping: cannot resolve dev01.corporate.ad: Unknown host
However - if I ping the IP address of a resource across the L2TP VPN tunnel (i.e. 10.14.51.24), I'm able to communicate with the resource:
64 bytes from 10.14.51.24: icmp_seq=0 ttl=128 time=36.063 ms
We are using the native VPN client built into Mac OS X 10.7/10.8. Inside the VPN profile, we have correctly configured the DNS settings (DNS Server - 10.14.51.20, Search Domain - corporate.ad), but we keep encountering this issue.
The temporary workaround we have given to our employees is to run the following commands in Terminal on their personal Mac when they experience this issue:
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
After they run those two commands, they are able to successfully access corporate resources using their hostnames/FQDNs.
However - it's not really a solution...

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
Third-party system modifications are a common cause of usability problems. By a “system modification,” I mean software that affects the operation of other software — potentially for the worse. The following procedure will help identify which such modifications you've installed. Don’t be alarmed by the complexity of these instructions — they’re easy to carry out and won’t change anything on your Mac. 
These steps are to be taken while booted in “normal” mode, not in safe mode. If you’re now running in safe mode, reboot as usual before continuing. 
Below are instructions to enter some UNIX shell commands. The commands are harmless, but they must be entered exactly as given in order to work. If you have doubts about the safety of the procedure suggested here, search this site for other discussions in which it’s been followed without any report of ill effects. 
Some of the commands will line-wrap or scroll in your browser, but each one is really just a single line, all of which must be selected. You can accomplish this easily by triple-clicking anywhere in the line. The whole line will highlight, and you can then copy it. The headings “Step 1” and so on are not part of the commands. 
Note: If you have more than one user account, Step 2 must be taken as an administrator. Ordinarily that would be the user created automatically when you booted the system for the first time. The other steps should be taken as the user who has the problem, if different. Most personal Macs have only one user, and in that case this paragraph doesn’t apply. 
Launch the Terminal application in any of the following ways: 
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.) 
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens. 
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid. 
When you launch Terminal, a text window will open with a line already in it, ending either in a dollar sign (“$”) or a percent sign (“%”). If you get the percent sign, enter “sh” and press return. You should then get a new line ending in a dollar sign. 
Step 1 
Triple-click the line of text below on this page to select it:
kextstat -kl | awk '!/com\.apple/{printf "%s %s\n", $6, $7}' | open -ef 
Copy the selected text to the Clipboard by pressing the key combination command-C. Then click anywhere in the Terminal window and paste (command-V). A TextEdit window will open with the output of the command. If the command produced no output, the window will be empty. Post the contents of the TextEdit window (not the Terminal window), if any — the text, please, not a screenshot. You can then close the TextEdit window. The title of the window doesn't matter, and you don't need to post that. No typing is involved in this step.
Step 2 
Repeat with this line:
{ sudo launchctl list | sed 1d | awk '!/0x|com\.(apple|openssh|vix\.cron)|org\.(amav|apac|cups|isc|ntp|postf|x)/{print $3}'; echo; sudo defaults read com.apple.loginwindow LoginHook; echo; sudo crontab -l; } 2> /dev/null | open -ef 
This time you'll be prompted for your login password, which you do have to type. Nothing will be displayed when you type it. Type it carefully and then press return. You may get a one-time warning to be careful. Heed that warning, but don't post it. If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator. 
Note: If you don’t have a login password, you’ll need to set one before taking this step. If that’s not possible, skip to the next step. 
Step 3
{ launchctl list | sed 1d | awk '!/0x|com\.apple|org\.(x|openbsd)/{print $3}'; echo; crontab -l 2> /dev/null; } | open -ef 
Step 4
ls -A /e*/{cr,la,mach}* {,/}Lib*/{Ad,Compon,Ex,Fram,In,Keyb,La,Mail/Bu,P*P,Priv,Qu,Scripti,Servi,Spo,Sta}* L*/Fonts .la* 2> /dev/null | open -ef  
Important: If you formerly synchronized with a MobileMe account, your me.com email address may appear in the output of the above command. If so, anonymize it before posting. 
Step 5
osascript -e 'tell application "System Events" to get name of login items' | open -ef 
Remember, steps 1-5 are all copy-and-paste — no typing, except your password. Also remember to post the output. 
You can then quit Terminal.