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Old 03-14-2007, 11:57 AM   #1
Registered: Oct 2003
Location: West Midlands, UK
Distribution: Slackware 14 (Server),OpenSuse 13.2 (Laptop & Desktop),, OpenSuse 13.2 on the wifes lappy
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Firewall prevents dhcp server from operating, plus other problems.

Hi all,

I suppose this might well belong in the networking forum, but as it also relates to my use of Slackware, i guess this is the best place for it, so here goes.

I have a box setup up with the following servers running:-


I also have a firewall running using iptables. Now my problem is that when the firewall is active, the dhcp server doesn't serve any IPs, and only by stopping it with /etc/rc.d/rc.firewall stop can I get the dhcp server to allocate IPs when requested
Thats problem No. 1 and the most important to solve.

Secondly, the squid proxy server doesn't seem to do transparent proxying when apache is running, and so just some advice on this issue. As I understand it, most, if not all web browsers are looking for http requests on port 80, which is where my apache serves its pages to, and also where squid expects tranparent redirection requests to be called from. To save having to set up each browser on the network to utilise the proxy address, this seems to be how squid needs to operate. So if I change the port that apache is running on to overcome this, how do I then get the webserver index page to be served just by entering the site address as I had previously done, or would I now need to append the address with the port No.

Hope this makes sense to someone, and looking forward to the answer.

Old 03-14-2007, 12:21 PM   #2
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RE: problem # 1 - I can't recall the exact contents of the default rc.firewall script, but I do recall it being well commented. If it allows/provides for RULES to be added or changed (which I'm fairly sure it does) then you would need to create rule(s) to allow incoming and outgoing packets on the ports and protocols necessary for the DHCP server to communicate and respond on.
I use LutelWall firewall in my Slackware, which provides VERY easy configuration of incoming and outgoing rules for every protocol there is, and what ports are used for what. But most firewalls allow for similar configuration.
As a last resort on this subject, you may want/need to implement the iptables rules yourself, but the firewall should allow for it in a much simpler way.

Problem # 2 - Seems you need a redirection in Apache, such that when it receives requests at
123.456.789.321 it would redirect them to the IP & port they should actually be going to. Like an alias. But, this is better suited to someone else for really accurate info So hopefully atleast the firewall info helps a bit!
Best of luck..
Old 03-15-2007, 11:24 AM   #3
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regarding the first issue, the ISC DHCP daemon isn't affected by iptables rules (although maybe things have changed now)... if you are using another dhcp daemon, such as dnsmasq or something, you need rules like this:
iptables -I INPUT -p UDP --dport 67 --sport 68 -j ACCEPT
iptables -I OUTPUT -p UDP --dport 68 --sport 67 -j ACCEPT
the second rule is of course optional depending on your setup...

regarding the second issue, i don't think i've had enough coffee yet so i'm not positive that i understand the issue correctly - but wouldn't you be able to work-around it by having your apache listen on a different IP (alias)??

Last edited by win32sux; 03-19-2007 at 12:45 PM.
Old 03-19-2007, 01:53 AM   #4
Registered: Oct 2003
Location: West Midlands, UK
Distribution: Slackware 14 (Server),OpenSuse 13.2 (Laptop & Desktop),, OpenSuse 13.2 on the wifes lappy
Posts: 778

Original Poster
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Thanks to both of you for the suggestions made. a change to the firewall rules as suggested by win32sux has done the job as far as the DHCP server is concerned. And the other problem with using Apache with Squid, with them both using port 80 was solved by following the advice I found here:-


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