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I have a PPTD server (pptpd) running on Debian and my clients are either Windows or Mac OS X machines. I also have an internal DNS hosted at the PPTP server since I want to resolve internal machines.

It runs smoothly all the time, except for a few DNS issues from time to time where the clients cannot resolve any of the internal domains for 10-20 seconds, then all works fine, then it happens again and so on.

The server is always up and a tcpdump 'udp port 53' never shows anything when I try to 'dig' the internal machines, so I'm not sure how to troubleshoot.

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UDP requests that fail from the requester to the server will probably not register at the server as it will probably not be detected at the server, which can occur over the PPTP session.

One possible approach to minimizing its affects is to consider increasing the TTL of DNS hosts entries. This should also decrease the UDP traffic across the VPN session as well.

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that's actually a neat idea, i'll give it a try and reply back –  Haytham Elkhoja Jul 30 '11 at 15:31
    
If is works, where it should unless your hosts are rapidly changing/updating their IP addresses, the difficulties should only show up at a maximum of once during any PPTP session. –  user48838 Jul 30 '11 at 15:41
    
it kinda works :) –  Haytham Elkhoja Jul 31 '11 at 13:49
    
Well, hopefully better than it was. Localized DNS caches may be the other option outside of improving the link in between. –  user48838 Jul 31 '11 at 15:01
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