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Re: [K12OSN] firewall question



I've run into this kind of problem before. Assuming server C is a dual-nic system, if you look carefully at the firewall rules I think you will see that eth0, for the clients, allows all connections, as it should be. eth1, on the other hand, usually blocks all incoming traffic except what is ESTABLISHED or RELATED (those are formal iptables terms; I'm not yelling or adding emphasis). As I recall, what has probably broken on your system is the FORWARD chain having no rules, and/or a kernel setting (/proc/net/ip_conntrack?) being turned off. The result is that your thin clients work, because their apps are running on the server and thus the traffic only goes via the OUTPUT chain; but other clients, like those coming from the wireless connection and then through the server, are not getting their traffic forwarded. I don't have access to a system ATM to more fully check/recall the details. Probably the most expedient thing to do would be to jump onto the #ltsp channel on IRC (there's a link and instructions at the ltsp.org website) and ask the folks there.

Peter

Vi Thai wrote:
There is no firewall for the entire school.  This K12LTSP server
contacts the Openserver for students and staff to log in.  The
Openserver has a firewall with only eth0 (private) being trusted so do
the K12LTSP servers even need to have their firewalls turned on?  The
reason why I ask is because all the thin clients can log on fine now.
The firewall settings for the K12LTSP servers are set to trust
nothing, not even NFS or Samaba, and they are still able to log on.
However now I am not able to get wireless to work on any of these
servers now.  Before when the firewall was turned off I was able to
get wireless to work behind "server c" but now that I've turned on the
firewall on all k12ltsp spervers, wireless no longer works if I plug a
wireless router into a switch on "server c."  I don't want to expose
the entire system just get a handful of students wireless access.
Thanks for everyones input.  I really appreciate it.

Vi

2008/3/1 Kemp, Levi <lnkemp bolivar k12 mo us>:
-----Original Message-----
 From: k12osn-bounces redhat com on behalf of Vi Thai
 Sent: Fri 2/29/2008 6:58 PM
 To: k12osn redhat com
 Subject: [K12OSN] firewall question

 Hi everyone!  I'm the technology coordinator of a small school in
 Glenburn, Maine.  I have two separate but related issues.
 1...
 I recently changed the firewall settings on three of my k12ltsp
 servers that are running Fedora 6.  I received this message from my
 network manager from server a: "outbound port tcp/22 (secure shell)
 scanning detected."  I'm not really sure what this meant, so I looked
 at the firewall settings on this particular server and noticed that
 one of the trusted ports was SSH, which I read uses port 22.  We only
 allow users to login from clients from within ou
 r school and no one from outside school can log in, so I didn't think
 turning off SSH would be a problem.  After turning SSH off some of the
 clients on the server could not log in.  I reset the server and
 everything was back to normal.  Is this what I should have done to
 address the message I received?  There hasn't been an update since the
 summer so should I do a "yum update" in the terminal to ensure that
 all software on the server is updated?
 2...
 I then went to look at the firewall settings for the other two servers
 ("server b" and "server c") and noticed that neither of the firewalls
 on the servers were even on!  I quickly changed the settings so that
 the firewall was enabled with no exceptions.  I reset the server and
 everyone was able to connect after the restart.  I thought everything
 was fine until a few minutes later when a teacher called and indicated
 that she couldn't get onto the wireless airport out in her portable (I
 had put an apple wireless airport out there plugged into the WAN port
 which was plugged into a switch on "server c").  The airport was
 working fine before I turned on the firewall and even if turn the
 firewall off I still cannot get the airport to work.  Anyone have an
 thoughts on how I could solve this issue.  I really don't want to turn
 the firewall off even though it has been on since I've been here last
 October.  My suspicion is that the firewall has been disabled for over
 two years now with no apparent problems.  We have been having a
 network slow down so perhaps there has been a compromise on one of
 these servers and I have not been informed yet.  I know it's a silly
 question, but should this firewall even be turned on?  I'm new to this
 type of network and any help provided would be greatly appreciated.

 Vi

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  I'd have to look it up but I recall someone asking this question before. The issue was with clients, both thin clients and regular fat clients on the DHCP side of the server not getting through. The solution was to open up ports on that NIC, the internal one so that all the traffic on the internal network could get through. I believe they used Webmin to do this easier. This should allow you to keep the external firewall on to protect the server and allow anyone on the inside to get through.
  As far as you second question goes, do you have an external firewall for the entire school? If so having one on your K12LTSP server may not be necessary, but if you can get it working it couldn't hurt.

 Levi

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