Re: [Openvpn-users] Push multiple DNS-servers

[Peter R. <rab...@ra...>]

Jan Just Keijser wrote:
> Antonis Tsolomitis wrote:
>> Jan Just Keijser wrote:
>>> Jonathan Petersson wrote:
>>>  
>>>> Is it possible to push multiple DNS-servers? I tried to add 2 push 
>>>> directives unsuccessfully (2.1.0.10-beta14)
>>>>
>>>>     
>>> this is definitely possible. Getting your operating system to use 
>>> them is a different matter. For Linux you'd need some 
>>> update-resolv-conf script, for Windows it is actually quite hard. I 
>>> routinely used
>>>   net stop dnscache
>>>   net start dnscache
>>> to get my XP box to recognize the DNS servers pushed by openvpn.
>>>   
>>
>> I am just curious: Isn't this the job of
>>
>> push "dhcp-option DNS a.b.c.d"
>>
> On Windows, the option "dhcp-option DNS a.b.c.d" will cause openvpn to 
> notify the Tap-win32 adapter to set DNS=a.b.c.d ; and after starting, an 
> 'ipconfig /all' does indeed show that the correct DNS server(s) are set. 
> However, for obscure reasons Windows does not immediately starts *using* 
> these new DNS servers. The only way I could find to trigger that is by 
> stopping and starting the dnscache service. To me, this sounds like a 
> Windows feature/bug that openvpn can and should not attempt to fix.
> 
> As for other OSes, updating the system DNS servers is quite OS 
> dependent, although there's an update-resolv-conf script that works fine 
> on most Linux flavours.
> 

What you are describing has to do with the dnscache service trying to be
smarter than it actually is. This is the registry import I use to solve
this (known to work on XP and Vista):

; Disabling the DNS caching service seems to break some obscure programs.
; Although the resolver is terribly broken (does not honor _ANY_ server
; supplied TTLs, does not do proper round-robin, etc.) it seems that this is
; indeed a necessary service. Here we try to tune it so it will behave.
; source: http://support.microsoft.com/kb/318803
; source: http://support.microsoft.com/kb/320760
; source: http://www.speedguide.net/read_articles.php?id=158
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache]
"Start"=dword:00000002
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters]
"MaxCacheTtl"=dword:0000003c
"MaxNegativeCacheTtl"=dword:00000000
"ServerPriorityTimeLimit"=dword:00000000
"NetFailureCacheTime"=dword:00000000
"NegativeSOACacheTime"=dword:00000000


My 2c