A networking program that controls the incoming and outcoming stream of data in a computer.
13
votes
2answers
4k views
How does reverse SSH tunneling work?
As I understand this, firewalls (assuming default settings) deny all incoming traffic that has no prior corresponding outgoing traffic.
Based on Reversing an ssh connection and SSH Tunneling Made ...
10
votes
4answers
1k views
Why do we need a firewall if no programs are running on your ports?
When I try to telnet to a port on a server, and if there is no program listening on that port telnet dies with a "Unable to connect ... " error. I understand that. But, why do we need a firewall if ...
9
votes
3answers
711 views
Is there a way to find which iptables rule was responsible for dropping a packet?
I have a system that came with a firewall already in place. The firewall consists of over 1000 iptables rules. One of these rule is dropping packets I don't want dropped. (I know this because I did ...
8
votes
4answers
470 views
iptables on tor exit node
I want to run an open Tor router.
My exit policy will be similar to ReducedExitPolicy.
But I also want to make it hard for the tor network to abuse my resources.
Cases I want to prevent clients ...
6
votes
4answers
3k views
Fail2ban block with IPtables doesn't work on Debian Lenny. [moved ssh port]
I've recently decided to do some security maintenance. I saw my logs, and there were some tries against my SSH server. At first, I moved away the SSH port from the default 22. After it, I read ...
6
votes
3answers
312 views
SpamAssassin Under Linux VPS
I am getting bald with this guys:
On a Linux VPS (CentOS), I have setup a mail server (Exim+Dovecot+Clamav+SpamAssassin) but scanning mail for spam using SpamAssassin is proving to be a challenge.
I ...
5
votes
4answers
2k views
Debian: Which firewall for a newbie?
I have to install a firewall on my server (so without X Server). It's a debian lenny. If it is possible, I want to avoid the use of iptables. Is there a way to install/configure a firewall for a ...
5
votes
4answers
464 views
How can I send spoofed packets in Linux
In order to test a firewall, I want to send malformed packets to its interface, regardless of my routing table.
Is there a way to ask linux "send this exact tcp package, to this MAC address, ...
5
votes
2answers
292 views
Configuring a vncserver so it's only accessible from my ssh tunnel
Since I use vnc through an ssh tunnel, is there any way I can block the open vnc port that the remote machine is listening on without it affecting my ability to use the ssh tunnel? Both machines are ...
5
votes
1answer
323 views
Opening port 80 but remain secure
I have a standard installation of Ubuntu 10.04, and have installed the LAMP stack so I can do some web development locally. On my router I have opened port 80 so I can develop with external services ...
5
votes
2answers
2k views
Per process firewall?
I've been reading around but can't seem to find a way to create per-process firewall rules. I know about iptables --uid-owner but that only works for outgoing traffic. I've considered scripting ...
5
votes
1answer
2k views
Uncomplicated Firewall (UFW) and UPNP
Is it possible to configured UFW to allow UPNP between computers in the home network?
Everything works if I turn off the firewall. I can see in syslog the firewall is blocking me. I've tried all ...
5
votes
1answer
620 views
ipfw : Traffic Shaping
I'm not sure what but it seems like I'm doing something wrong... my objective is to be able to limit some of my traffic, to be exact www traffic. One of my clients os running what's called a ...
4
votes
2answers
928 views
Preventing program from using internet
Is there a way to block certain programs from being able to connect to the internet in Debian (a firewall blocking outgoing connections), so for example, to block a windows program running in wine ...
4
votes
4answers
3k views
Set some firewall ports to only accept local network connections?
Basic firewall question:
How do I set up the firewall on a system in a LAN so that some ports are only open to connections from the local area network, and not from the outside world?
For instance, ...
4
votes
1answer
2k views
Difference between SNAT and Masquerade
I am confused what's the actual difference between SNAT and Masquerade?
If I want to share my internet connection on local network than whether should I select SNAT or Masquerade?
Give me some ...
4
votes
2answers
2k views
What prevents a machine from responding to pings?
I have a CentOS release 5.4 linux box on Amazon EC2 that I'm trying to set up to be monitored via Nagios. The machine is in the same security group as the nagios server, but it seems to be ...
4
votes
2answers
243 views
How can I use one network port for VPN and the other for everything else?
My Linux machine has two network ports with two IP addresses. I want to use one port for my VPN and accounting, and the other port for other usages. How can I tell Linux not to allow any requests from ...
4
votes
2answers
775 views
What tools do I need to intercept and change an incoming packet on a WP2-Personal wifi hub
Which tools should I research into to intercept a plain text packet, edit it and then continue it on it's way. I am using Ubuntu 11.04 and Backtrack 5; my wifi is WPA2-person encrypted. I need to edit ...
4
votes
1answer
627 views
Force VPN using IPtables?
I want to force the use of VPN using iptables, therefore while VPN is disabled no outgoing traffic shall be allowed (except maybe some DHCP stuff...). Now i guess I could just block everything not ...
4
votes
1answer
947 views
Enable RTSP in iptables
I'd like to receive a RTSP stream via VLC, but when I try to run
sudo -u non_root_user cvlc -vvv -I dummy rtsp://ip:port/x.sdp
I get:
Unable to determine our source address: This computer has an ...
4
votes
1answer
1k views
Why doesn't my iptables rule work?
I have two interfaces on my VPS: eth0 and eth0:0. I want to block incoming packets on port 80 on eth0:0 using iptables. I tried this, but it doesn't work:
iptables -A INPUT -i "eth0:0" -p tcp ...
4
votes
2answers
2k views
How to limit P2P/torrent traffic on an OpenWrt 10.03 router?
We have a WRT160NL router with OpenWRT 10.03, and a 60-70 Mbit connection (from ISP, don't ask why). This router can do 30-35 Mbit on ethernet(i mean cable)..ok!
There are ~7 PC's using this Wireless ...
3
votes
3answers
256 views
Is it possible to simulate “no external access” from a Linux machine when developing?
Sometimes I upload an application to a server that doesn't have external internet access.
I would like to create the same environment in my machine for testing some features in the application and ...
3
votes
1answer
650 views
Is berkeley packet filter ported to linux?
I am doing some research to figure out what distro's of linux contain kernel packet filtering and are compatible with BPF.
http://kernelnewbies.org/Linux_3.0
http://lwn.net/Articles/437981/
These ...
3
votes
1answer
237 views
How to understand why the packet was considered INVALID by the `iptables`?
I set up some iptables rules so it logs and drops the packets that are INVALID (--state INVALID). Reading the logs how can I understand why the packet was considered invalid? For example, the ...
3
votes
1answer
2k views
How to re-enable iptables on Fedora 18?
FirewallD is the default firewall in Fedora 18. I have been using iptables for quite some time and have a custom configuration which I need for logging of ip traffic. I am not used to the new ...
3
votes
2answers
390 views
How to listen to all ports (UDP and TCP) or make them all appear open in Debian
I got an external Debian server. The problem is that my university campus doesn't allow connections to go outside when the port is different than TCP port 22, 80, 443, or UDP port 123. I tested them ...
3
votes
1answer
187 views
iptables infographic
Is there an infographic somewhere that describes the logical flow of iptables? Specifically, I'm looking for something that diagrams which point in the process ip_conntrack applies.
3
votes
1answer
159 views
Linux App that monitors log and add rules to iptables
I used to use a linux software that monitors logs like http, ssh, etc and if it detects that someone is trying to use brute force, it blocks that ip by adding a rule to iptables. I forgot what that ...
3
votes
3answers
234 views
Turning an old computer into a network firewall
I have an old Dell Dimension with two ethernet cards, and I need to turn it into a firewall. I've tried FireStarter and IPCop, but I don't think I'm setting them up right.
Here's the setup that I'm ...
3
votes
4answers
75 views
How to check whether firewall opened for a port but not listening on the port
We will be deploying a new application to a Server and the application will be listening on port 8443. We have asked Network team to open the firewall for the port 8443 on that server before deploying ...
3
votes
1answer
1k views
How to configure pfsense to NAT servers?
How can I configure pfsense so it will NAT servers so they can be accessed outside of the company? I tried to play around with the NAT settings, but didn't get anywhere. I want to be able to access ...
3
votes
2answers
391 views
FreeBSD kernel nat or natd?
As I notice more often with FreeBSD, there are always plenty of ways that lead to some specific goal.
After figuring out which firewall I wanted (I choose ipfw) I now am completely insecure about ...
3
votes
1answer
305 views
Using rsync + cron to sync a machine behind a firewall with my dropbox
I have a machine (A) behind a firewall with no access to the Internet, on this machine I can NFS mount directories on another machine (B) which can access internet, and is accessible from Internet, ...
3
votes
1answer
135 views
Can I limit connections per second for certain UserAgents using UFW?
GoogleBot is hitting my server hard - and even though I have set the CrawlRate in Webmaster Tools it is still hiking up the load on my server and slowing down Apache for the rest of the normal web ...
3
votes
3answers
267 views
Can't add large number of rules to iptables
I made a very simple bash script (echo at start, runs commands, echos at end) to add approx 7300 rules to iptables blocking much of China and Russia, however it gets through adding approximately 400 ...
3
votes
2answers
1k views
How to limit number off ssh login attempts per time interval
I am trying to limit number of ssh login attempts per time period. How might I do that?
I have something like (in shorewall's rules)
#ACTION SOURCE DEST PROTO DEST ...
3
votes
2answers
231 views
Recommended reverse firewall applications for linux?
I'm looking for a reverse firewall, something like Little Snitch for Linux, but my google-fu is failing me. Does something like this exist on Linux? Many thanks.
3
votes
1answer
284 views
nmap shows me that one service is “open|filtered” while locally it's “open”, how to open?
I have a Quake 3 server. And it's launched successfully.
The problem is that no one can connect to that server.
I am running: nmap -sU -p 27960 hostname and it's showing me that it's state ...
3
votes
1answer
220 views
Setting up the firewall for amule on OpenBSD 4.7 gateway
I'm trying to properly setup the firewall on my gateway (OpenBSD 4.7) using pf to allow amule (on 10.0.0.104) to operate properly as discussed here:
Now I know pf has changed a bit from OpenBSD 4.7 ...
3
votes
1answer
33 views
IPTables - Port to another ip & port (from the inside)
I currently have a NAS box running under port 80. To access the NAS from the outside, I mapped the port 8080 to port 80 on the NAS as follow:
iptables -t nat -A PREROUTING -p tcp --dport 8080 -j DNAT ...
3
votes
1answer
280 views
How to “jail” a user account's network capabilities on Linux?
Linux box a is connected to a home DSL line with dynamic DNS registration, hosting a tmux session to which multiple clients connect in read-only mode over SSH. All users connect using the same ...
3
votes
2answers
510 views
How to check and block processes connecting to internet directly?
Is there a way to find which processes in my system are getting connected to net automatically. Is there a way to select and block net access of some processes permanently? I use mint 11. I use a USB ...
3
votes
1answer
404 views
Letting NFS through a FreeBSD PF firewall
I'm trying to configure my firewall (PF) on FreeBSD to let NFS traffic through.
I know that NFS uses both TCP and UDP to connect to the client along with a bunch of daemons that use random port ...
3
votes
1answer
256 views
Converting a line from a firewall on OpenBSD 4.9 to OpenBSD 4.7
What is the OpenBSD 4.7 equivalent of this line from OpenBSD 4.9 for use with pf?
no nat on egress proto udp from 192.168.1.10 port 4672 to any
3
votes
1answer
336 views
1000 iptables entries on CentOS?
I just got a new dedicated server with CentOS and I'm trying to debug some network problems. In doing so, I found over one thousand iptables entries. Is this the default on a CentOS system? Is there ...
3
votes
3answers
480 views
tunneling VNC/rdesktop over ssh
I'm having a friend behind a firewall, with a windows computer. I'm having a Linux machine at home which is not behind a firewall.
I want to have an rdesktop connection to his machine, without using ...
3
votes
0answers
124 views
IPFW Port Forwarding
This is my situation: I want to connect to an OpenVPN server from my office (we're using a proxy, only ports 80 and 443 are allowed).
Server IP address is: 176.31.250.232:843
My static IP address ...
3
votes
1answer
298 views
Outgoing firewall application similar to Little Snitch for Mac
Is there a Linux application similar to Little Snitch? Little Snitch is an outgoing firewall that temporarily blocks outgoing network requests until the user decides whether to allow the connection or ...
