creating a basic dns client/server system, help!

Hi,

noob here.. I'm required to create a very basic DNS server with DNS client software, using Java, for my college project. I may or may not be following standards such as how BIND resource records are formatted etc etc, since i'm doing my own server, a very basic one at that.

Here is my summarized personal thinking and learning experience, which I hope someone can give me pointers for..

1) Not sure how my Server can capture name resolution requests from my resolver client (another pc). I don't know how the Windows 'DNS Client' service of the resolver formats the messages, do i have to know?

2) What if i have to create my own client-side software? I learned of the Windows service "DNS Client" that intercepts name resolution requests made by any program (such as IE?), formats it and sends it to the preferred DNS server, and waits for a response.

3) If i have to create my own client, do i have to disable the DNS Client service? However i do not know how my custom client resolver may intercept these name resolution requests.

Any advice is greatly appreciated. Pls do let me know if i really do not seem to know what i am talking about. =).

lol! You have to write a DNS server AND client in java for school?!?! That's one tough mother of a teacher you've got there. He/She probably expects you to use the java object library to do this with. It's not too hard in terms of client stuff, but I have no idea if it can setup a basic DNS server without some socket stuff going on.

Well, if you were asking about the Visual Basic, C, or perl language, then I would hook ya up with some example code. But I don't really have a use for java, so you're kinda on your own in that. This isn't a programmer forum after all, and therefor you're not likely to get your help here. Go ask your question on a java forum somewhere so that you'll get ahold of people more familiar with the java object library.

Hi SilentRage,

Thanks for the reply =). I did ask the Java forums, but i'm still waiting for a reply. Anyway I was trying to get my java proggie (my DNS server to-be) to listen on port 53, with the intention of getting the DNS queries from clients.

Problem is, port 53 is already being used, my guess is that some Window DNS thingie is already using it. I want to make the port free for my own usage, but i'm not sure what or where to disable.

Windows help offered a command called 'set port' or something under nslookup, that changes the port for the Windows DNS from the default '53' to a user specified value. However, i think its safer to disable the service rather that changing the port, god knows what might happen.

Any idea? Is any of this advisable?

p.s: I'm sure BIND listens on port 53 right? =p

Thanks again

All DNS servers listens on port 53. If Microsoft DNS Server is installed and running as a service then it would be the reason port 53 is used. If you can't figure out how to get rid of that port 53 process, then download TCPView from www.sysinternals.com . It is like a GUI form of netstat except it'll also tell you what process created that socket.

If you try to terminate the process that TCPView tells you is using port 53, and you get a permission denied error, then let me know and I'll give ya a hardcore tip on smacking down those processes which think you can't terminate them using the task manager.

IT WORKS.. for now =)

Thanks a zillion SilentRage.

I don't think there are many newbies here, but if anyone is interested, here's what i did:

Here is what i did.

I could not find any the port "53" being displayed anywhere in TCPView, but after some research i found out that 53 falls under the the 'domain' group of ports.

From this website:
http://www.portsdb.org/bin/portsdb....Y&String=domain
I found that ports classified under 'domain' are port 53, 256, 1863, and 9909.

According to TCPView there were 3 services using 'domain ports'. 1 used TCP, the other 2 used UDP. The services as displayed by TCPView are as follows:

posadissrv.exe:1940 TCP advo1800:domain
posadissrv.exe:1940 UDP advo1800:domain
SVCHOST.EXE:1032 UDP advo1800:domain

I still needed to find out which was using 53.

In DOS i did a
netstat -an |find /i "listening"
(http://www.petri.co.il/quickly_find..._open_ports.htm)

There was only one entry for port 53, and i found that something was listening that port using TCP.

Being the most obvious choice, i ended the following service from within TCPView:
posadissrv.exe:1940 TCP advo1800:domain

Doing that also cancelled the same service that was using UDP..

Anyway, i could freely use port 53 after that. Hooray.

Or you could've checked an option in TCPView and it would've displayed port numbers instead of port names.

ack!

=P