named listening on UDP

[Kal Feher]

You can force BIND to use a specific port for queries and/or transfers with
the "query-source" and "transfer-source" options statements. However my
feeling is that this invites trouble.
As a point of interest, assuming your DNS server resides behind a NAT
firewall, you could look at the translation table to confirm that the source
port is the result of an outbound connection (as observed by the firewall).
That should satisfy your paranoia ;)


On 4/4/07 8:21 AM, "Peter Dambier" <peter at peter-dambier.de> wrote:

> Tom Schmitt wrote:
>> Hi,
>> 
>> I have a (maybe) simple question, but google couldn't help me, so I try the
>> list:
>> 
>> I downloaded Bind 9.3.4 and installed it on a Linuxserver (Debian-Etch). It's
>> working fine. (Thank you for this piece of fine software!)
>> 
>> Because I'm a little bit paranoid I checked the ports where named is
>> listening. netstat -tanp brought what I expectet: Port 53 on the external
>> interface and port 53 and port 953 (for rndc) on the localhost-interface.
>> 
>> But netstat -uanp surprised me a little bit. Besides the expected ports 53 on
>> the localhost and the external host, named is also listening on UDP-port
>> 33186 on the external port. What is that for? I know of no reason to open
>> this port. (also, named is listening on udp6-port 33187)
>> 
>> Can anyone tell me what the purpose of this open port is?
>> 
>> Thanks,
>> Tom.
> 
> Sometimes named queries other nameservers e.g. the root-servers. Like any
> other program
> named uses a random port to query this other nameserver on port 53.
> 
> Very likely, next time you start it, named will use a different port.
> 
> Kind regards
> Peter and Karin
> 

-- 
Kal Feher