iptables is the userspace command line program used to configure the Linux 2.4.x and 2.6.x IPv4 packet filtering ruleset. It is targeted towards system administrators. Please, when asking a question about iptables, add the output from the following command: iptables -L -v -n

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Can you recommend a good intro to iptables? [closed]

I have to setup a firewall on a Linux server (all my previous experience is with Windows). My rules are meant to be pretty simple - forbid all, allow some ports with all, allow some ports for specific ...
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1answer
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iptables: difference between NEW, ESTABLISHED and RELATED packets

Part of a firewall on a server : iptables -A INPUT -p tcp --dport 22 -m state NEW --state -m recent --set iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --update --seconds 100 ...
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4answers
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Good iptables starting rules for a webserver?

I am installing a new centos 5.4 server and I would like to have a set of clean rules for mu iptables to startup. What would be the good rules to start with? Is this a good starting point : # ...
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6answers
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Use IPtables or null route for blacklisting about 1 million IP addresses?

I've come across a situation where a client needs to blacklist a set of just under 1 million individual IP addresses (no subnets), and network performance is a concern. While I would conjecture that ...
9
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3answers
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Throttle bandwidth via iptables

I have a need to throttle the bandwidth usage, similar to how some ISPs do it, so that after a couple of seconds, it throttles down the speed.
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4answers
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how do I disable the nf_conntrack kernel module in CentOS 5.3 without recompiling the kernel

I'm running CentOS 5.3 and want to disable the nf_conntrack module to improve network performance for haproxy. I'm running iptables with some simple rules. I don't really need the connection ...
5
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2answers
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Stop DoS attacks with an IP tables rule?

I was wondering if I could prevent small (D)DoS attacks with a simple IP tables rule? By small I mean that they are flooding my web server with about 400+ requests from one or two IP addresses. I ...
56
votes
5answers
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I accidentaly forbid SSH connection to a remote server… What's next?

Let's say it again, we all make mistakes, and I have just made one. A brief history: I was doing some stuff on a VPS (Debian) I'm renting, when I noticed some strange behaviour. Using the netstat ...
12
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3answers
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How to configure a custom NAT for use in Amazon VPC

I have an Ubuntu box I wish to use as NAT instance (among other things). I would prefer to avoid using the NAT AMIs provided by Amazon, and instead configuring NAT myself. Currently, my host has a ...
13
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3answers
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Debugging rules in Iptables [duplicate]

How can I know how many packets were dropped by my iptables rules ?? Is there any debugging mechanism to see which rule is Dropping my packet or Accepting it ??
8
votes
3answers
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Iptables - Bridge and Forward chain

I have setup ethernet bridge br0 that contains two interfaces eth0 and tap0 brctl addbr br0 brctl addif eth0 brctl addif tap0 ifconfig eth0 0.0.0.0 promisc up ifconfig tap0 0.0.0.0 promisc up ...
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3answers
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Should I rate-limit packets with iptables?

I'm using iptables on Ubuntu Server. It's a web server on a VPS. I'd like to know if I should rate-limit packets. If so, what should I rate-limit? And should I do so globally or per IP address? ...
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4answers
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How do you PREPEND an iptables rather than APPEND?

Pretty basic question.. How do you PREPEND an iptables rather than APPEND? I have DROP statements at the bottom of my rules. I have software to add new rules but adding rules after DROP statements ...
8
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2answers
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iptables | Types of ICMP: which ones are (potentially) harmful?

I read that certain types¹ of ICMP packets can be harmful. Questions: Which ones and why? How should I layout an iptables ruleset to handle each type of ICMP packet? Should I rate-limit any of these ...
8
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1answer
14k views

Difference beetween DNAT and REDIRECT in IPTABLES

Okay, it may be because I am dense or maybe just not finding the right source, but I can't understand why one of these IPTABLES setups would be better than the other. Here is my setup: I have a box ...
6
votes
1answer
3k views

Bind process or user to specific IP (Linux)

I have 3 non-root users on my server, and I want to give to each of them the different IP addresses (I have multiple IPs on one network inteface). For example, user1 will have 192.168.1.2, user2 - ...
3
votes
1answer
7k views

iptables allow all outgoing - still can't resolve dns or make a http request

I have setup iptables this way: Table: mangle Chain PREROUTING (policy ACCEPT) num target prot opt source destination Chain INPUT (policy ACCEPT) num target prot opt source ...
11
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3answers
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Cannot Set UID on Shell Scripts

Can anyone help me find out what is going on here? I have some rules set up tracking packet counts. When I run the following script as root: #!/bin/bash iptables -t mangle -xnvL I get the output ...
4
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1answer
5k views

How to create UDP proxy using iptables

I have a server running UDP server on port 50000. This server receives updates from clients, and pings back the clients every 5 seconds to the socket they were connected from. Now I want to redirect ...
3
votes
3answers
4k views

Advanced routing problem

I have 2 internet links using 2 ADSL routers and I need to give access to the Internet for the 192.168.0.0/24 network. I have to route outgoing traffic based on port number, protocol, … using ...
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4answers
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How To Set iptables log rules for PSAD with UFW?

For PSAD to work, I need to add the following iptables rules and enable packet logging : iptables -A INPUT -j LOG iptables -A FORWARD -j LOG ip6tables -A INPUT -j LOG ip6tables -A FORWARD -j LOG I ...
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3answers
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Only allowing traffic from Cloudflare

I am new to Linux System Administration and I am experimenting with iptables trying to learn how to really lock down a system with them. And one thing a friend of mine recommended was that there was a ...
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3answers
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Debugging iptables and common firewall pitfalls?

This is a proposed Canonical Question about understanding and debugging the software firewall on Linux systems. In response to EEAA's answer and @Shog's comment that we need a suitable ...
9
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3answers
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How do you test iptables rules to prevent remote lockout and check matches?

As I'm learning about iptables I've made a couple of mistakes and locked myself out. What method(s) do you use to test rules without locking yourself out? I'm using ubuntu server 12.04 LTS All ...
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3answers
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Iptables: “-p udp --state ESTABLISHED”

let's look at these two iptables rules which are often used to allow outgoing DNS: iptables -A OUTPUT -p udp --sport 1024:65535 --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT iptables -A ...
6
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1answer
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PPTP VPN iptables firewall issues csf [closed]

I am having a problem with iptables and a PPTP VPN, I have read related topics both on hear and online but still can't get it to work! I am trying to set up PPTP on an ubuntu server on our local ...
3
votes
3answers
2k views

Service can't connect to self using public IP, NAT problem

I have a dedicated server from serverloft.eu, but due to some network security I cannot use bridge networking on my server. So I have setup all my IPs to the main eth0, and used NAT to forward trafic ...
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1answer
1k views

Is there any way to filter packets (eg. by iptables) after routing is complete?

I want to drop certain packet destined to an ip_address AFTER it has reached the POSTROUTING chain. However, for iptables, the "nat" table cannot be used for filtering so the following doesn't work: ...
1
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4answers
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iptables: IP alias and port forwarding

I can't figure out iptables and I don't know very much about networking and I'm really hoping that someone out there can help me. I have a server with two ip addresses associated with it: 1.1.1.1 and ...
7
votes
5answers
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Copying packets from an interface to another

I have a Linux system (let it be A) with 2 ethernet cards, namely eth0 and eth1 which are attached to two totally unrelated LANs. Basically eth0 is used for normal application traffic and eth1 is ...
6
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3answers
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Firewall questions about state and policy?

I finally managed to install my VM host and now I am messing with iptables to create, test and learn. Does it matter if i put the below rules at the begin or at the end of my rules ? $IPT -P INPUT ...
5
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2answers
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How many rules can iptables support?

Someone asked me this recently and I had no answer for it. I know this is kind of an open-ended question but is there a limit on the numnber of rules you can install in a table/chain? If so, how can I ...
5
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3answers
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iptables — OK, **now** am I doing it right?

This is a follow up to a previous question where I asked whether my iptables config is correct. CentOS 5.3 system. Intended result: block everything except ping, ssh, Apache, and SSL. Based on ...
4
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2answers
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iptables redirect local connections to remote system / port

I am trying to use SSH to port forward windows machines local port 3389 to a redhat server on some arbitrary port (in the unprivileged region) I have protected behind a firewall, then forward the ...
3
votes
3answers
217 views

Iptables rules with ! character

I have entered iptables rules to log a specific connection on our server, but it doesn't seem to be working as I want it to. Here are the rules: 1 LOG tcp -- !10.51.0.0/16 ...
3
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1answer
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How do I allow only certain IPSet set's to access a certain port with iptables?

I'm using IPSet to build IP ranges for different countries as follows : # Canada ipset -F ca.zone ipset -N ca.zone nethash for IP in $(wget -O - http://www.ipdeny.com/ipblocks/data/countries/ca.zone) ...
3
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3answers
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How to log the ip addresses trying to connect to a port?

Is it possible to log all ip addresses that trying to connect or connected to port "5901" in linux debian? how can i do that? Regards
3
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2answers
224 views

ipTables: How to improve the current set-up?

It took a lot of time and digging to get my ipTables working fairly well. Current status: 'Works' w/ a noticeable, reproducible (almost unacceptable) delay on SSH connections. This delay goes away as ...
2
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2answers
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iptables packet forwarding to one of two gateways depending on origin

Given the following installation: old router 192.168.1.1 with NAT forward of tcp port 80 to 192.168.1.10:80 new router 192.168.1.2 with NAT forward of tcp port 80 to 192.168.1.10:80 web ...
2
votes
2answers
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How can i forward the http and ssh port to my internal server using iptables

I do not have the router so i make the Linux system into router having centos 6.4 for forwarding the Public network traffic to my local LAN.It has the two NIC card. one for public ip (eth1) and ...
2
votes
1answer
6k views

OpenVPN not redirecting all traffic through VPN

I have just finished setting up my VPN, and google shows my IP to be that of my VPN, so this works fine. However, when I log in through SSH to the VPN server, it shows my last login to be that of my ...
2
votes
5answers
7k views

Route return traffic to correct gateway depending on service

On my office network I have two internet connections and one CentOS server running a website (HTTPS on port 443). The website should be publicly accessible through the public IP of the first internet ...
2
votes
1answer
6k views

iptables change destination IP without DNAT

I'm trying to workaround a broken application which insists on connecting to the private address (and thus unreachable) of a server, instead of connecting to the public address (even if the relevant ...
1
vote
3answers
719 views

Server Firewall preventing sending of email [closed]

The firewall on my VPS appears to be preventing my site from sending email. It was working fine until the end of last month. My hosting provider (Webfusion) has been next to useless. I am able to ...
1
vote
1answer
156 views

iptables logging doesn't log

I'm trying to log any requests to port 22 into my syslog, so I have following line in my iptables: LOG tcp -- anywhere anywhere tcp dpt:ssh LOG level debug yet, ...
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2answers
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Using iptables to redirect incoming requests from port 2525 to port 25?

I'm a developer working from home on an application. One of the features of my app is that it sends outgoing notification emails. I'm attempting to relay these messages through one of our company's ...
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3answers
3k views

fail2ban Error Gentoo

I've recently setup a new VPS running Gentoo (My first time using the distro so please forgive me is this is a really easy one) and as I've done with other servers installed fail2ban. Setting it up to ...
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2answers
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iptables redirected port 80 to 8080 - How to disallow direct access to port 8080?

I've routed all requests from port 80 to port 8080 for my Tomcat server using iptables. iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080 Now http://mydomain.com/ ...
10
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4answers
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iptables nat does not exist

Today my iptables nat on the host system stopped working and I have no clue what happend! (That's very bad, I know) All commands are executed as root user. If I run $ iptables -t nat -L I get the ...
5
votes
1answer
5k views

iptables drop packet by hex string match

I got this packet captured with tcpdump but I'm not sure how to use the --hex-string param to match the packet. Can someone show me how to do it? 11:18:26.614537 IP (tos 0x0, ttl 17, id 19245, offset ...