Mac OS X, VPN and DNS problems
Recently I had a weird problem on my laptop. Web browsing was slow and certain lookups failed altogether. The failures were exclusively associated with nominet.org.uk domain names, specifically connections to our office network. When the problems first started my mail client failed to work unless the VPN was activated, which is not the way our security policy mandates it should work. After a while the mail client failed even after activating the VPN. I was effectively locked out of my email unless I visited the office!
The error messages from the mail client suggested that the DNS lookup for the mail server was timing out. Using wireshark on the wireless interface I noticed that there were no DNS lookups for nominet.org.uk, though other search domains were being appended. Everything in System Preferences looked fine, /etc/resolv.conf had no surprises. However, I did find a suspect file: /etc/resolver/vpn-resolver-662638-0 which contained:
domain nominet.org.uk
nameserver 213.248.199.17
timeout 3
This file dated from early 2006, which seemed odd as the laptop was only installed in March 2008! I presume it was copied over from my previous laptop by the Migration Assistant. Removal of this file fixed the problem, but where did it come from?
Our present VPN solution is based on OpenVPN and I use the Tunnelblick client to connect. My first thoughts were to blame this combination. There have been some stability problems with Tunnelblick on Leopard, apparently. But, before we used this system we used an SSL VPN solution terminating on a Netscreen firewall. I used the VPN Tracker client from Equinux to connect. I now believe the rogue resolver file was left behind by VPN Tracker after it was deleted. I am still at a loss to explain why it took so long to start affecting the laptop, or why it appeared to degrade in stages, rather than just fail.
- DNS , OSX , Lotus Notes
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