Iptables is a module that provides the Linux operating system functions of firewall, NAT and logging of data traveling over a computer network.

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Is there a decent diagram of packet flow for a modern era (2.6+) iptables setup?

I'm currently trying to debug a particularly hairy set of DNAT based iptables rules (the UDP reply never makes it back to the original requester) and I'm struggling to visualise the packet flow ...
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69 views

iptables -L lags on non localhost or anywhere address

I am trying to configure iptables for ubuntu 10.04 and I have a problem with iptables -L lagging on rows where the destination or source address is not localhost or anywhere. The following entries ...
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2k views

Reverse Proxy for TCP (RDP, VPN, etc) and HTTP

I have a domain that points to my ISP assigned IP though a CNAME (cname goes to my noip address incase my ISP decides to change the IP), I would like to route different subdomains to various IP:PORT ...
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106 views

iptables rule cannot be added

Is there anything wrong with these rules? They cannot be added to iptables, no error but they just don't show up in iptables -vnL iptables -I FORWARD 1 -s 1.2.3.4 -p udp -m connlimit ...
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1k views

Will increasing number of rules in iptables slow down my internet

How much impact will the rules have on speed, if we are using match to queue the packets.
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321 views

internet connection gone after $ iptables -F INPUT

I have a PC with two Ethernet cards, and I was trying to configure my eth1, but when I typed $ iptables -F INPUT, the internet was gone on eth0. Does anyone has any idea how to get my internet ...
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1k views

How to match multiple strings in iptables

I have 2 strings, and i wish to queue the packet if it contains both the strings ( something like ("jsh"&&"gjhyg")), i tried following ways, but they don't seem to work: sudo iptables -A ...
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112 views

How to redirect local connection to my things in IPv6 on linux?

With IPv4 I can make some program connect to my service instead of where it wants using REDIRECT and DNAT targets in OUTPUT chain in iptables (sometimes combined with -m owner) In IPv6 hovewer I ...
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192 views

Is it possible to figure out which http request generated the corresponding response

I am using iptables to listen to tcp (http) packets. I am filtering out INPUT responses containing a matching string. Is it possible to know which http request generated the response. Assuming 10 ...
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221 views

iptables: understanding the rationale behind its tables and chains

I'm going through the iptables tutorial and am currently at Chapter 6, Traversing of tables and chains. I'm having trouble understanding the why's behind Tables 6-1, 6-2, and 6-3 listed in the above ...
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110 views

Separating two networks

I have two routers, R1 and R2. R1 (a stock linksys router running dd-wrt) is connected to internet and is serving internet to a network of 5 devices/PCs running a DHCP server, with a network of ...
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1k views

Gateway on a virtual network interface used by LXC guests

I'm currently having some problems with configuring a gateway for a virtual network interface. Here is what I've done : I created a virtual network interface : # brctl addbr lxc0 # brctl setfd lxc0 ...
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591 views

Iptables - having trouble opening port 443

I am attempting to set up https, but I am having difficulty opening that port. Nmap scan report for localhost (127.0.0.1) Host is up (0.000073s latency). PORT STATE SERVICE 443/tcp closed https ...
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3k views

pfctl port forwarding in Mac osx?

-A PREROUTING -s 10.0.10.0/24 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8080 -A PREROUTING -s 10.0.10.0/24 -p tcp -m tcp --dport 443 -j REDIRECT --to-ports 8080 -A POSTROUTING -s 10.0.10.0/24 -o ...
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440 views

Router 2wire, Slackware desktop in DMZ mode, iptables policy aginst ping, but still pingable

I'm in DMZ mode, so I'm firewalling myself, stealthy all ok, but I get faulty test results from Shields Up that there are pings. Yesterday I couldn't make a connection to game servers work, because ...
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267 views

How to enable iptables with verbose mode in DD-WRT?

I want to log all packets to messages through iptables. Can you help me how to set verbose mode in DD-WRT. Just DYI, I have optware installed to store the large messages file and do log rotation.
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1answer
338 views

What other ports should I block to maximize server security? PS using IPTABLES

I have blocked ports 80, 9001, 9080. What other ports should be blocked to maximize security? PS: It is a asterisk server / PBX Sorry: New Systems Admin here :) Thanks!
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42 views

Networking - In what scenarios do “RELATED” connections occur?

I am trying to use iptables and ip6tables to establish basic networking security on my webserver. However, I am having a hard time understanding the RELATED state of the conntrack module... I know ...
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632 views

blocking port 80 via iptables

I'm having problems with iptables. I am trying to block port 80 from the outside, basically plan is we just need to Tunnel via SSH then we can get on the GUI etc. on a server I have this in my rule: ...
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98 views

Use port forwarding with masquerade

I'm using a debian as a router with nat configured. How can I set up port forwarding, to set an rdp server on the local network for example?
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140 views

Linux route/IPtables with internal VM network

I am having some trouble figuring this all out. I have Windows 7 [10.10.30.1] ROUTER [eth0=192.168.4.134 eth1=10.10.30.254] Ubuntu [192.168.4.143] I can ping eth0 and eth1 from Win7, and also ...
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738 views

Filezilla not showing directory listing?

I had downloaded iptables from server to my windows desktop .I edited some lines for opening port (2195) .after download i added some line for enabling port using this link ...
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173 views

Is this a decent set of IPTables rules?

Can anyone please point out to me whether, assuming that the needs for a given (Ubuntu 12.04) server are only SSH, NTP (client), HTTP(S) and system updates (apt-get or aptitude), the following set of ...
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27 views

A dumb about iptable

I saw a iptable command like this: iptables -t nat -A xx -p tcp -m tcp --dport 80 -j DNAT --to %myweb%:80 what's "%" there for? Thanks. Where I can get a manual to tell me what kind of symbols I ...
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iptables firewall only allows internet traffic if source port of 80 is allowed

I am configuring an iptables firewall, currently just to allow http and https traffic. It is working but under a particularly strange rule - I must allow incoming connections with a source port of ...
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394 views

Ubuntu iptables web browsing

I am trying to build iptables to protect my system. After I save my iptables, I cannot connect to any web page (through browser or wget). Is it perhaps related to DNS? I tried to access ...
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1k views

iptables - Allowing Established Sessions?

I'm learning how to use iptables on ubuntu server. Can you please explain to me what "Allowing Established Sessions" means and why should I include it in rules? sudo iptables -A INPUT -m conntrack ...
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iptables: Allow only HTTP access for web browsing

Have a linux box, want it locked down but just be able to surf internet on it. Why is this script blocking http too? #!/bin/sh # # iptables -F # #Set default policies for INPUT, FORWARD and OUTPUT ...
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688 views

Iptables port mapping from two PCs to one

We have 3 PCs, two of it are connected to internet (both of it have 2 NIC) PC1: eth0 - 1.0.0.1 (external IP) eth1 - 172.16.0.1 (internal IP) PC2: eth0 - 1.0.0.2 (external IP) eth1 - 172.16.0.2 ...
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787 views

Rerouting traffic from port 80 to another port on a single ip

I have a server with multiple IP addresses associated with it. I'm trying to run a node.js web server (which I do not want to run as root), using only one of those ip addresses (it would be very bad ...
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679 views

DHCP Client Can't Find DHCP Server

I currently have 3 machines: CentOS (router) eth1 - 18.0.168.1 eth2 - 145.165.34.1 Windows Server 2008 (server) 18.0.168.2 DHCP scope - 145.165.34.10 - 145.165.34.20 Windows 7 (client) Supposed ...
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609 views

Linux Iptables Routing

I need help with a problem. My setup is: CentOS (Router) eth1 18.0.168.1 255.255.248.0 eth2 145.165.34.1 255.255.254.0 Windows Server 2008 18.0.168.2 My problem is from the Windows machine, I ...
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iptables - How to forward all external ports to one local port

I want a service to be running on every external port on my system. Since it wouldn't work to start 65535 single instances of that service (I guess...) I thought of using iptables for this. The ...
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2k views

What means empty iptables?

I'm using CentOS and when type the command: iptables -L -v The output is as follows: Chain INPUT (policy ACCEPT 19614 packets, 2312K bytes) pkts bytes target prot opt in out ...
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IPv4, IPv6 and IPTables

I have just recently learned that even if I block all traffic to my webserver using iptables it is still vulnerable to external attacks via IPv6. In my understanding, this renders iptables-only ...
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94 views

NATing with a single-homed machine possible?

I have the following setup: a) a single-homed machine, A, that can see the Internet. b) other machines B, C, and D that cannot see the Internet. c) A, B, C, and D can see each other. d) all ...
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200 views

How to read iptables -L output?

I'm rather new to iptables, and I'm trying to understand its output. I tried to RTFM, but to no avail when it comes to little details like these. When iptables -vnL gives me a line such as: Chain ...
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2k views

Port forwarding with IPTABLES and VBox

I have a small problem with getting a proper configuration of iptables under Ubuntu. But before, let me describe the network configuration: I am using xDSL line terminated with modem+router+DHCP ...
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2k views

Implementing a global proxy with iptables

I'm running a Linux box (Lubuntu 12.04) in an Windows environment where a pac file is used to configure internet access. proxy.pac file: function FindProxyForURL(url, host){ var proxy_yes = "PROXY ...
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4k views

Deny all incoming connections with iptables?

I want to make some simple iptables rules to deny all incoming connections and allow outgoing. How can I do that?
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309 views

How to setup IPtables to allow capture network traffic from a virtualbox VM configured with NAT

I would like to have a VirtualBox virtual machine that can't get online. I want to be able to monitor all network traffic attempts from the Linux host. So, if the virtual machine attempts to make a ...
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781 views

linux drops packet when trying to route it - why?

I track packets using LOG targets for all chains of all tables and the last chain I see my packet in is the POSTROUTING chain of the mangle table: mangle_PREROUTING: IN=eth0 OUT= ...
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198 views

Using my previous desktop computer as custom ubuntu router, will throughput be high?

I'm going to be redoing my home network soon and am thinking of using a dedicated ubuntu machine to use as the router/firewall as well as being a web server, nas (media file server), dns, wifi, and ...
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4k views

How to alias an IP address to make DLNA resource accessible from different IP network

what I have I have a home wifi network 192.168.1.0/24 having DLNA resource 192.168.1.100. I have a TV with ethernet and a netbook with both wifi and ethernet interfaces. I want to make my notebook ...
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iptables vs route

What's the difference between these two tools? Can anybody tell me what the main workflow of networking behind Linux (in relation to IPv4 packet filtering, NAT and IP routing table) is?
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666 views

Internet Connection Sharing bypassing MAC Filter in Ubuntu Linux

My university gives me an internet connection by Ethernet, DHCP but they have installed MAC Filtering to allow only using my PC. I have a wireless router TL-WR340GD. which has MAC address cloning ...
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65 views

Regulate outgoing ip traffic on a VM

I am making a virtual network setup for my high school cybersecurity team to practice. I am connecting all the VMs together through a VPN and then people who are practicing will VPN in and ssh/remote ...
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114 views

Mark packets across computers?

I use Transmission on Ubuntu and I'm having this issue, which basically says that QoS is broken because there is no way to limit which outgoing ports uses. I was thinking of doing a dirty and ugly ...
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225 views

Push local traffic “outside” the nat

I have a server functioning as my nat that hosts some services. When I locally connect via UDP to this server it my client uses the public ip but the server answers with its local ip. So the question ...
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2k views

Allow access from outside network with dmz and iptables

I'm having a problem with my home network. So my setup is like this: In my Router (using Ubuntu desktop v11.04), I installed squid proxy as my transparent proxy. So I would like to use dyndns ...