iptables allow creation of rules to define packet filtering behavior.

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12
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Can I limit a user (and their apps) to one network interface?

As the title really. I've actually got two scenarios to apply this: Multiseat Desktop: two network connections both with internet gateways and two accounts doing bandwidth-intensive tasks on each. I ...
12
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2answers
4k 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 ...
11
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4answers
2k views

Block network access of a process?

Is it possible to block the (outgoing) network access of a single process?
11
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2answers
9k views

Reply on same interface as incoming?

I have a system with two interfaces. Both interfaces are connected to the internet. One of them is set as the default route; a side effect of this is that if a packet comes in on the non-default-route ...
10
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3answers
3k 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 ...
10
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1answer
507 views

Is it better to set -j REJECT or -j DROP in iptables?

There's an example of iptables rules on archlinux wiki: # Generated by iptables-save v1.4.18 on Sun Mar 17 14:21:12 2013 *filter :INPUT DROP [0:0] :FORWARD DROP [0:0] :OUTPUT ACCEPT [0:0] :TCP - ...
9
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3answers
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Only allow certain outbound traffic on certain interfaces

I have rather an odd issue. I have a server with two network interfaces eth0 and eth1. Each are connected to a different network. Each network has a internet gateway. The server has various outbound ...
9
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3answers
13k views

Output traffic on different interfaces based on destination port

My question is basically the same as Only allow certain outbound traffic on certain interfaces. I have two interfaces eth1 (10.0.0.2) and wlan0 (192.168.0.2). My default route is for eth1. Let's say ...
9
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2answers
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iptables --set-mark - Route diferent ports through different interfaces

Short story, 3 interfaces, eth0 (LAN), eth1(ADSL), eth2(4G). eth0 -> eth1: Works (ports 80, 443, 4070) eth0 -> eth2: Doesn't happen This is a graphical representation of the idea: Port 80 & ...
8
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2answers
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What do numbers in INPUT,FORWARD,OUTPUT chains mean in iptables config file?

I came across the following config file: # Generated by iptables-save v1.3.1 on Sun Apr 23 06:19:53 2006 *filter :INPUT ACCEPT [368:102354] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [92952:20764374] -A ...
8
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1answer
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Linux as router with multiple internet providers

Linux as router: I have 3 Internet providers, each with its own modem. Provider1, which is gateway address 192.168.1.1 Connected to linux router eth1/192.168.1.2 Provider2, gateway address ...
8
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1answer
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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 ...
8
votes
1answer
1k views

Dual network connection

I have a usb cellular modem and a Home LAN connection on my Ubuntu 10.10 box. Both work independently. I want to know how to have both connected at the same time, and be able to specify which ...
8
votes
4answers
722 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 ...
7
votes
3answers
92 views

Limit max connections per IP address and new connections per second with iptables

We have an Ubuntu 12.04 server with httpd on port 80 and we want to limit: the maximum connections per IP address to httpd to 10 the maximum new connections per second to httpd to 150 How can we ...
7
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2answers
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Iptables to allow incoming FTP

i want to allow incoming FTP traffic. CentOS 5.4: This is my /etc/sysconfig/iptables file. # Generated by iptables-save v1.3.5 on Thu Oct 3 21:23:07 2013 *filter :INPUT ACCEPT [0:0] :FORWARD ...
7
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2answers
10k views

iptables: allow certain ips and block all other connection

How do I allow certain ips and block all other connection in iptables?
7
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1answer
976 views

Shaping outgoing traffic with iptables

On my laptop, when I run any downloads, torrents, etc, browsing is crippled. I read somewhere that you could configure your iptables powered router to prioritize certain network traffic. Could I do ...
7
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2answers
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How to restrict internet access for a particular user on the lan using iptables in Linux

Let's say there are two users on the LAN, A and B. How do I restrict user A from internet access using iptables rules and saving the rules so that after reboot, they are still effective. And suppose I ...
7
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1answer
2k views

What is the difference between -m conntrack --ctstate and -m state --state

I'm reading this howto, and there's something like this: We can allow established sessions to receive traffic: $ sudo iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT ...
7
votes
1answer
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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 ...
7
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4answers
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+300

iptables rule adviser script

There is a server without any iptables defense: ACCEPT all.. There could be custom applications on this server. If we should need to harden this server (so deny all, and only let what is needed by ...
7
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4answers
564 views

Failing to block brute force ssh with iptables

I'm trying to block (slow down) brute force attacks on my sshd server. I'm following this guide http://www.rackaid.com/resources/how-to-block-ssh-brute-force-attacks/ which basically says I need to ...
7
votes
1answer
134 views

What is the difference between -j DROP and -j STEAL?

I often see that people set STEAL target in iptables rules. It's possible to get this target by installing (on debian) xtables-addons-common and xtables-addons-dkms. I was curious why people prefer ...
7
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1answer
444 views

iptables will match the following ICMP request packet as ESTABLISHED state after the first reply packet is sent

Test environment: CentOS 6.3 - kernel 2.6.32-279.el6.i686, iptables v1.4.7 Win7 <---> CentOS Windows is constantly replaying ICMP echo request in 10pkt/sec rate to CentOS. In iptables, I added the ...
7
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1answer
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Why are incoming packets on a TAP interface seen with tcpdump but not with iptables?

A program injects packets on a Linux TAP interface (these packets are coming from a virtual machine). Specifically, these are DHCP requests (so they're UDP). I can see the packets with tcpdump but not ...
6
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2answers
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Iptables: matching outgoing traffic with conntrack and owner. Works with strange drops

In my iptables script I have been experimenting with writing as finely grained rules as possible. I limit which users are allowed to use which services, partly for security and partly as a learning ...
6
votes
3answers
7k 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 ...
6
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2answers
2k views

Is it possible to redirect a logging output of the iptables' LOG chain into a separate log file?

I don't want to mix iptables's log output with other system logs. How could I specify a dedicated log file for iptables LOG chains output?
6
votes
2answers
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iptables, how to redirect port from loopback?

The main rules are: OUTIF=eth0 /sbin/iptables --policy INPUT DROP /sbin/iptables --policy FORWARD DROP /sbin/iptables --policy OUTPUT ACCEPT /sbin/iptables -A INPUT -i lo -j ACCEPT ...
6
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4answers
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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
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1answer
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NAT (Internet connection sharing) switching between multiple public interfaces

My Ubuntu 12.04 (precise) laptop has three network interfaces: eth0: wired interface sometimes connected to the Internet wlan0: wireless interface sometimes connected to the Internet vboxnet0: wired ...
6
votes
1answer
2k views

Terminal commands equivalent to NetworkManager's “Use as Hotspot” option

I'm making a gui application which will control my laptop in order to make it act as a wifi hotspot. I may change distributions so I want to find a solution which will work generally for all ...
5
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2answers
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Why do iptables rules disappear when restarting my Debian system?

I add this rule: sudo iptables -t nat -A OUTPUT -d a.b.c.d -p tcp \ --dport 1723 -j DNAT --to-destination a.b.c.d:10000 When restart computer rules are deleted. Why? What I can do to make ...
5
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4answers
8k 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, ...
5
votes
3answers
1k views

Transform an UDP unicast packet into broadcast?

We need to wake-up some computers on our internal LAN, from the Internet. We have a somewhat closed router. Very few ways to configure it. I'd like to use netfilter (iptables) to do this because it ...
5
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4answers
1k 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
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4answers
2k views

How to share the internet connection?

An ordinally network topology in picture: In words: - "server" (e.g.: an Ubuntu 10.04 LTS) is connected to the "internet" through pppoe connection - "server" is using it's wireless card in AP ...
5
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3answers
330 views

Does Fedora's firewall use iptables?

Fedora has a Firewall Configuration interface: Does this use iptables underneath to enforce the rules?
5
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2answers
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How to redirect kernel messages having the unique id substring into separate log file (using `rsyslog`)?

I am using iptables's logging feature to debug my network activity. I use certain prefix with --log-prefix parameter to uniquely identify messages in kernel log belonging to iptables output, for ...
5
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3answers
3k views

Why can't I use the REJECT policy on my iptables OUTPUT chain?

I currently have my OUTPUT chain set to DROP. I'd like to change it to REJECT, so that I have a clue that it's my firewall stopping me from getting somewhere rather than a problem with whatever ...
5
votes
1answer
614 views

iptables beginner question about ACCEPT

I'm just reading up on iptables, finally. I'm a little confused because the input chain from the filter table (as installed, fedora 17), looks like this: target prot opt source ...
5
votes
2answers
106 views

Why are some ports reported by nmap filtered and not the others?

I'm scanning a server which should have a pretty simple firewall using iptables: by default everything is DROPped besides RELATED and ESTABLISHED packets. The only type of NEW packets allowed are TCP ...
5
votes
4answers
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iptables rules not reloading on CentOS 6.x

I have one single ipset added to my iptables on a CentOS 6.x box and this rule is lost when the machine reboots. I've found this answer showing how to make a Ubuntu system reload the iptables rules ...
5
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1answer
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iptables port-mirroring

I need to be able to get a copy of packets received on port 8001 to port 8002. I have tried the following but I get an error that --tee is undefined. sudo iptables -t nat -A PREROUTING -p TCP -s ...
5
votes
1answer
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How to reset all iptables settings?

Are there any simpler commands to these? (e.g.: a oneliner? can one command reset iptables/netfilter settings to this?) IPTABLES="$(which iptables)" # RESET DEFAULT POLICIES $IPTABLES -P INPUT ...
5
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2answers
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Help configuring a custom log file for iptables

I'm trying to log dropped packages to a custom file instead of /var/log/messages. To achieve this, I have added these two lines at the end of my configuration file: -A INPUT -m limit --limit ...
5
votes
1answer
418 views

Creating a NAT from loopback to a remote server

My goal is to redirect connections from the local host to a remote server, and be able to change the remote address on the fly, without any client config changes. I can do this now using a nat on the ...
5
votes
1answer
111 views

Skip routing via `lo` interface for outgoing packets

Introduction I have following load balancing configuration: 10.0.1.31 - lb 10.0.1.35 - virtual IP 10.0.1.32 - node1 (tomcat + mysql) 10.0.1.33 - node2 (tomcat + mysql) I'm using keepalived which ...
5
votes
1answer
2k 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 ...