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Author Topic: BIND DNS server on TCP or UDP?  (Read 1674 times)


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BIND DNS server on TCP or UDP?
« on: April 26, 2009, 07:23:23 am »


I have lauched BIND server on my computre to see how it works.
Then I scanned my host to see which ports were open and I saw that the 53  was open as TCP port.
I always read that DNS is working on UDP, so how can it handle UDP requests if it is accpeting only TCP packets?

Code: [Select]
bash-3.1# nmap localhost

Starting Nmap 4.60 ( ) at 2009-04-26 16:02 GMT
Interesting ports on localhost (
Not shown: 1712 closed ports
53/tcp  open  domain
631/tcp open  ipp
953/tcp open  rndc

Then I scanned with netstat and it shows that the port 53 is open as an UDP port.

Code: [Select]
bash-3.1# netstat -anu
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State     
udp        0      0 *                         
udp        0      0*                         
udp        0      0  *                         
udp        0      0*                         
udp        0      0  *                         
udp        0      0    *                         
udp        0      0 *                         
udp        0      0   *

So I am confused, how can it be TCP and UDP at the same time?
Which tool is wrong? Or it's me?

If I send an UDP packet does it will accept while running in TCP mode?

Thank's in advance

I know that theorically UDP packets are for short requests and TCP packets are for zone tranfer.


  • Vectorian
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  • Posts: 1877
Re: BIND DNS server on TCP or UDP?
« Reply #1 on: April 26, 2009, 07:46:17 pm »

A port can be open for TCP, UPD or both.