Question

How to reload hosts file to refresh DNS Cache during application run

Asked by: DasDirector

I have a utility written using C# that -

Makes HTTP requests
Edits and saves the hosts file
Repeats the above

The problem is the changes to the hosts file are not being used by the new http requests being made by the application unless I restart the application. I also issue the ipconfig /flushdns after writing the hosts file.

 Any clues?

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Asked On
2008-07-10 at 06:57:20ID23553725
Tags

Microsoft

,

.NET

Topics

Domain Name Service (DNS)

,

.Net Editors & IDEs

,

Microsoft Visual C#.Net

Participating Experts
1
Points
0
Comments
12

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Answers

 

by: DasDirectorPosted on 2008-07-10 at 07:00:44ID: 21973465

Here is the C# code to refresh DNS that is called after the hosts file is resaved -

System.Diagnostics.Process proc = new System.Diagnostics.Process();
proc.EnableRaisingEvents = false;
proc.StartInfo.FileName = "ipconfig";
proc.StartInfo.Arguments = "/flushdns";
proc.Start();

 

by: RobWillPosted on 2008-07-10 at 20:18:08ID: 21979709

I am afraid I am no help at all with the programming end of it but changes to the Hosts file should be immediate upon saving. They should be available for the very next DNS query. There is no need to "reload" it but using the #PRE option does pre load it for faster responses, but I know of no way of doing so after boot. It almost sounds as if your application loads the hosts file contents which is why it requires restarting.

I assume the entires do work? The hosts file has a few idiosyncrasies such as requiring a carriage return at the end of each line for it to work.
http://msmvps.com/blogs/robwill/archive/2008/05/10/lmhosts-and-hosts-files.aspx

 

by: DasDirectorPosted on 2008-07-11 at 06:08:39ID: 21981993

I have separated the process that makes the HTTP requests from the one that is editing and saving the hosts file; this ensures that the latest entries in the hosts files are used.

I had tried earlier to call 'ipconfig /flushdns' from within a single process, but it was not using the lastest entries from the hosts file.

 

by: RobWillPosted on 2008-07-11 at 06:17:32ID: 21982066

as soon as you make the change try form a command line
nslookup  name.domain.abc
It should work immediately, or there is an issue with how the hosts file is formated.

 

by: DasDirectorPosted on 2008-07-15 at 08:54:21ID: 22008159

nslookup in this case returns the IP address of the Load balancer (that is what I would I have expected). I am connected via VPN to the server farm hosting the servers and am interested in pinging the web-servers individually, in this case I use the internal IP address and sequentially ping each of them.

I have a work around; after changing the host file, I issue requests from another process that takes in the new values in the hosts and send requests to the newly mapped IP.

 

by: RobWillPosted on 2008-07-16 at 06:24:47ID: 22015636

Sounds like you have 'resolved' the problem?

 

by: DasDirectorPosted on 2008-07-16 at 08:54:46ID: 22017184

Yes, as mentioned not an elegant solution, but it works correctly.

 

by: RobWillPosted on 2008-07-17 at 05:13:25ID: 22024533

Glad to hear, but I appreciate your wanting something "cleaner".
--Rob

 

by: DasDirectorPosted on 2008-07-18 at 08:24:44ID: 22036793

Thanks for your comments; although I did not get to the clean solution learnt a bit anyway.

 

by: RobWillPosted on 2008-07-18 at 08:26:41ID: 22036822

As did I  :-)
Cheers !
--Rob

 

by: DasDirectorPosted on 2008-07-21 at 15:46:46ID: 22055069

I'm unsure about why am i being asked to post "objecting using the text entry box below "? As mentioned in my responses, I implemented my workaround that works correctly.

20120131-EE-VQP-002

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