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macos - VPN messes up DNS resolution


After connecting with the Kerio VPN client (OS X Leopard) to a server, the internet (~web browsing) stopped working for the client.


After poking around, the issue seems to be bad DNS server (i.e., entering IPs directly works). After disconnecting from the VPN, the invalid DNS server disappears from scutil --dns and all's well again.


Now, I don't understand why OS X on the client even changes the DNS settings -- internet should be routed through a different interface, through the default gateway, not through the VPN.


Questions:



  1. By what mechanism does connecting the VPN client change the "default" DNS server?

  2. How can I stop the VPN client from changing routing/DNS rules? Where is this stuff stored/modified?



Before VPN:


$ scutil --dns
DNS configuration

resolver #1
  nameserver[0] : 10.66.77.1 # <---- default gateway = home router; all good
  order   : 200000

resolver #2
  domain : local
  options : mdns
  timeout : 2
  order   : 300000

...

VPN connected:


$ scutil --dns
DNS configuration

resolver #1
  nameserver[0] : 192.168.1.1 # <--- rubbish
  nameserver[1] : 192.168.2.1
  order   : 200000

resolver #2
  domain : local
  options : mdns
  timeout : 2
  order   : 300000

...

The VPN doesn't appear among $ networksetup -listallnetworkservices. It also doesn't appear in the "Network" dialogue of System Preferences. ifconfig reports it as


kvnet0: flags=8842 mtu 1400
inet 192.168.2.9 netmask 0xffffff00 broadcast 192.168.2.255
ether 44:45:53:54:4f:53


EDIT: progress -- according to Kerio VPN docs:


The VPN server also assigns the client an address for the primary, and
optionally also secondary DNS server and DNS domain extension. This 
allows to specify remote hosts with their names.

The change of DNS configuration has such effect that all DNS queries 
from the client host are sent to a DNS server in a remote private 
network. Users usually do not even notice any change. Upon closing of
the VPN connection, the original DNS configuration will be recovered.

How do they do that, and how do I stop them from doing it (switch DNS back without closing the VPN)?



Answer



"Solved" by a complete reinstall (Lion OS instead of Leopard).


I still have no idea what the problem was, but may it rest in peace...


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