Latest LQ Deal: Complete CCNA, CCNP & Red Hat Certification Training Bundle
Go Back > Forums > Linux Forums > Linux - Security
User Name
Linux - Security This forum is for all security related questions.
Questions, tips, system compromises, firewalls, etc. are all included here.


  Search this Thread
Old 12-08-2003, 09:34 PM   #1
Registered: Oct 2002
Distribution: RedHat 9
Posts: 43

Rep: Reputation: 15
firewall prevents dns access

Hi Everyone,

I upgraded to RH9 a few months back and have had a lot of trouble getting my dialup connection up and running again, I've managed to solve all of the problems except one which is related to my firewall. I can't access/ping any websites by name, only by numerical address, which sounds like a DNS problem. If I either turn off my firewall completely, or issue an "ipchains --flush" as root, then everything works fine.

disabling my firewall to get on the net sounds like asking for trouble to me. There must be a way to allow DNS packets through but keep the rest of the stuff out. I've tried bringing the firewall security level down to medium and allowing incoming DHCP, but that didn't help. Does anyone know how I can fix this?

I would greatly appreciate any suggestions you might have. Many thanks in advance.
Old 12-08-2003, 09:51 PM   #2
Senior Member
Registered: Oct 2003
Location: Zurich, Switzerland
Distribution: Debian/unstable
Posts: 1,357

Rep: Reputation: 47
Is your /etc/resolv.conf looking ok? Is it ok to recieve dns queries (domain/53)?
Old 12-08-2003, 10:02 PM   #3
Registered: Oct 2002
Distribution: RedHat 9
Posts: 43

Original Poster
Rep: Reputation: 15
Hi ToniT,

thanks for your reply. I'm still a bit of a newbie so I'm not sure how things should look. This is what my /etc/resolv.conf looks like:

nameserver #kppp temp entry
nameserver #kppp temp entry

and these nameservers work fine as long as my firewall is down. Am I missing something in this file?

Thanks for your help.
Old 12-08-2003, 11:46 PM   #4
Senior Member
Registered: Jul 2003
Location: Silicon Valley, USA
Distribution: OpenBSD 4.6, OS X 10.6.2, CentOS 4 & 5
Posts: 3,660

Rep: Reputation: 69
ipchains is deprecated. If you're using a 2.4.x kernel you want to use iptables. iptables should be doing stateful inspection so you shouldn't have to modify the firewall at all. In fact, your problem is pretty bizarre because if you can get all traffic except DNS, there shouldn't be any reason why DNS specifically is blocked.

In any case, you need to allow outbound connections to 53/TCP & UDP. If your firewall is not behaving statefully (really weird) then you need to allow return responses from 53/TCP & UDP to ports (TCP and UDP) over 1023. Again, if you have a stateful firewall, you won't need to do any of this.


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Suse 9.2 firewall prevents 'ping' on local network? Steerpike SUSE / openSUSE 5 11-27-2004 05:56 PM
GNOME prevents access to XSL files andymadigan Debian 2 08-03-2004 08:35 PM
app launched at boot not prevents access to login screen wvmikep Linux - Newbie 5 07-03-2004 07:41 AM
DNS and Firewall dexter_modem Linux - Security 8 11-13-2003 10:41 PM
DNS and firewall merlin371 Linux - Networking 2 07-31-2003 05:36 AM

All times are GMT -5. The time now is 06:27 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration