Project Home
Project Home		 Wiki
Wiki		 Discussion Forums
Discussions		 Project Information
Project Info
Networking/Discussion/General/DNS Lookup. How can we disable Reverse DNS lookup in QNX/List of Posts
Forum Topic - DNS Lookup. How can we disable Reverse DNS lookup in QNX: (4 Items)
   
Update
Sajal Malhotra(deleted)
02/11/2015 7:51 AM
post113290
DNS Lookup. How can we disable Reverse DNS lookup in QNX   
Hi,

When I try to ftp (or telnet as well) to my QNX host it takes about 60 secs before I really get the connection.
Looking at Wireshark Logs i see that the host generates Reverse DNS Lookup packets towards DNS Servers configured in 
resolv.conf. (e.g. Queries of type 130.255.168.192.in-addr.arpa).
I do need DNS Server for Domain Name Resolution however there is no need for Reverse lookups.
Is there any way to disable these Reverse Lookups?

Thanks and Regards
Sajal Malhotra
Attachment: Text ReverseDNSLookupPackets.pcap 780 bytes
Gervais Mulongoy
02/11/2015 8:21 AM
post113293
Re: DNS Lookup. How can we disable Reverse DNS lookup in QNX   
You could probably achieve this using dnsmasq (check the 3rd party repo) 
locally where you point all your DNS requests to 127.0.0.1 and you 
configured dnsmasq with your real DNS servers and dnsmasq take care of 
handling the reverse lookups. That should speed things up for you.
Nick Reilly
02/11/2015 8:39 AM
post113294
Re: DNS Lookup. How can we disable Reverse DNS lookup in QNX   
ftpd supports the "-n" option to disable this behaviour
http://www.qnx.com/developers/docs/660/index.jsp?topic=%2Fcom.qnx.doc.neutrino.utilities%2Ftopic%2Ff%2Fftpd.html&
resultof=%22ftpd%22%20

Unfortunately telnetd doesn't have the same capability, it doesn't require name services but if it has them it will use 
them, see
http://www.qnx.com/developers/docs/660/index.jsp?topic=%2Fcom.qnx.doc.neutrino.utilities%2Ftopic%2Ft%2Ftelnetd.html&
resultof=%22telnetd%22%20
Sajal Malhotra(deleted)
02/19/2015 3:17 AM
post113337
Re: DNS Lookup. How can we disable Reverse DNS lookup in QNX   
Thanks Nick for your prompt response. 

We tried the -n option. However it seems that we have an old ftpd binary (Our HW has QNX v6.3.0 installed).
Is it possible to get the latest ftpd binary which supports this option?

I also discovered another workaround to prevent reverse lookup. Which is by defining the IP address to host name mapping
 in "/etc/hosts". This also then works for Telnet and FTP.
However the problem with this approach is that we also have to define the mapping of IP address of PC/Laptop which is 
connecting to our Host and from where we are doing the FTP. Now considering that my Host IP is fixed to 192.168.255.131,
 i need to create all entries in 192.168.255.0/24 subnet, because i am not sure what IP would be assigned to PC which is
 connecting to my host machine.
Is there any way to define 1 entry for a complete subnet in /etc/hosts file?

Return


  A subsidiary of BlackBerry             All content ©2004-2013, QNX Software Systems