iptables allow creation of rules to define packet filtering behavior.

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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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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
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1answer
621 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 ...
6
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1answer
95 views

Setting traffic class on return packets

I have a network topology: Server <-> router1 <-> router2 <-> router3 <-> edgeRouter <-> "internet" All routers are linux based, and support iptables. The server sets ...
6
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1answer
3k 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 ...
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3answers
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Blocking outgoing connects with iptables

I have a (non production) machine where external supporters have shell-access (non-root). I want to prevent them from going further on into our network from that machine using iptables. The "normal" ...
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3answers
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route traffic out different gateway by destination network

I have several gateways and would like to route some traffic out of different gateways based on its destination. I'm guessing I'd need to use a combination of iproute2 and iptables rules, but am not ...
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1answer
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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 ...
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Transform a UDP unicast packet into a broadcast?

We need to wake-up some computers on our internal LAN, from the Internet. We have a somewhat closed router, with very few ways to configure it. I'd like to use netfilter (iptables) to do this because ...
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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, ...
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4answers
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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 ...
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2answers
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How can I configure syslog.conf file, to log iptables messages in a separate file?

How can I configure /etc/syslog.conf file in order to save log information about iptables in a specific file. I want to save these information separately, so I can extract what I want easily and ...
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2answers
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incoming ACCEPT all iptables rule still appearing

I'm following this guide here: http://isalazyadmin.net/2009/07/02/configuring-a-basic-firewall-for-debian-linux/ And I have the iptables listed shown, but my server still appears to be accepting all ...
5
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340 views

Does Fedora's firewall use iptables?

Fedora has a Firewall Configuration interface: Does this use iptables underneath to enforce the rules?
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3k views

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 ...
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3answers
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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
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1answer
461 views

How does a transparent SOCKS proxy know which destination IP to use?

There are two SOCKS proxies that I know about that support transparent proxying for any outgoing TCP connection: Tor and redsocks. Unlike HTTP proxies, these SOCKS proxies can transparently proxy any ...
5
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1answer
836 views

Why should the ECN on your machine be disabled?

I was going through this article on iptables and there the author said that: It's important to turn off ECN (explicit congestion notification) so that Internet communications will work ...
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Is it better to set rules in ip6tables or disable ipv6?

I have the following network configuration: # ifconfig -a eth0 Link encap:Ethernet HWaddr 00:e0:1c:73:02:09 inet addr:10.1.4.41 Bcast:10.1.255.255 Mask:255.255.0.0 inet6 ...
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1answer
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How to Allow Outgoing SMTP on iptables Debian Linux

If I choose to allow all traffic on the OUTPUT chain (iptables -P OUTPUT ACCEPT) mail sends fine. As soon as I lock down my server with these rules, outgoing mail stops working. All else works though, ...
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2answers
2k views

Tunnel yum traffic through another server via ssh

I am running a Fedora desktop behind a corporate proxy that is blocking yum traffic (specifically *.gz and *.bz2). I have access to a separate RedHat machine via ssh which can download anything it ...
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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
590 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
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1answer
3k 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 ...
5
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1answer
416 views

Using source routing (LSRR) - any ideas?

What I want to do is conceptually very simple, but I can't find any information or help about how to go about doing this. Basically, I want to configure my networking to use source routing (LSRR). ...
5
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1answer
280 views

Is there a way to match an inet and inet6 IP set in a single rule?

Is it possible to have one IPv4 and one IPv6 IP set (ipset(8)) within the same rule? I have several rules that depend on one set of IPv4 addresses and another set of IPv6 addresses respectively, but ...
5
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1answer
553 views

What are the definitions of addrtype in iptables?

I am keen to use addrtype in combination with -src as a rule in one of my filter chain like so to drop some bogon ips: -A INPUT -p tcp --dport 80 -m addrtype --src-type UNICAST ! -s 127.0.0.0/8 -j ...
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2answers
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Whitelist IP's in CentOS 7

I want to setup CentOS 7 firewall such that, all the incoming requests will be blocked except from the originating IP's that I whitelist. And for the Whitelist IP's all the ports should be accessible. ...
4
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1answer
1k views

What's the difference between ULOG and NFLog?

Various places suggest to use ULOG or NFLOG instead of LOG for getting dedicated netfilter logging (see for example here or here). From looking at man iptables those two look quite alike. Except that ...
4
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1answer
5k views

What is the difference between OUTPUT and FORWARD chains in iptables?

CentOS 6.0 I'm studying iptables and am getting confused on the difference between FORWARD and OUTPUT chains. In my training documentation, it states: If you're appending to (-A) or deleting ...
4
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3answers
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How can I redirect ports 80 and 443 to 8080 and 8443 with iptables?

I'm looking at the documentation for a Tomcat 6 webapp called DSpace, specifically in regardds to running Running DSpace on Standard Ports (80 for http:// and 443 for https://) I am trying to use ...
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2answers
541 views

Why can I reach a different interface's IP address?

I'm wondering about this, and I can't seem to find an explanation on the internet. I have a linux gateway which has multiple interfaces: eth0: external ip eth1: 172.16.1.1/24 eth2: 172.16.2.1/24 ...
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2answers
346 views

Can iptables rules manipulate IP sets?

In iptables-extensions(8) the set module is described and it is discussed that it is possible to react to the presence or absence of an IP or more generally a match against an IP set. However, it ...
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1answer
465 views

How does iptables recognize packet state?

Consider these two sets of rules: Set A -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT -A INPUT -j REJECT -A OUTPUT -j ACCEPT Set B -A INPUT -m conntrack --ctstate ...
4
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1answer
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How to Block SSH Brute Force via Iptables and How does it work?

I'm planning to add the following rules to iptables to stop ssh brute force attack which are common these days. -A INPUT -i eth0.103 -p tcp -m tcp --dport 4522 -m state --state NEW -m recent --set ...
4
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1answer
810 views

Why is my computer trying to send ICMP type 3 to OpenDNS?

In my firewall logs I see lots of entries like this. IN= OUT=eth0 SRC=192.168.1.105 DST=208.67.220.220 LEN=148 TOS=0x00 PREC=0xC0 TTL=64 ID=55705 PROTO=ICMP TYPE=3 CODE=3 [SRC=208.67.220.220 ...
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1answer
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iptables: recent module

I am using the "recent" module to prevent port scanning, such as: -A INPUT -i eth0 -m recent --name PORTSCAN --update --seconds 60 -j DROP -A INPUT -i eth0 -p tcp -m tcp --dport 22 -j ACCEPT -A INPUT ...
4
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1answer
297 views

Can iptables be used to monitor TCP timeouts/resets system-wide?

I'm trying to determine if an application's connection to a database is internal to the application or due to a networking event. This seems like something netfilter would have system-wide visibility ...
4
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2answers
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Where is iptables script stored on DD-WRT filesystem?

I have an ASUS RT-N16 router that I've flashed with the open-source DD-WRT firmware. According to my ssh login, I'm running: DD-WRT v24-sp2 mega (c) 2010 NewMedia-NET GmbH Release: 08/07/10 (SVN ...
4
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2answers
311 views

What tool to execute a command on repeated syslog entries?

Occasionally, one VPS under my control gets bombarded with POP3 login attempts. They all fail, but the huge number of spawned processes and active connections pretty much amount to a DoS attack. When ...
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2answers
213 views

Why were tables built into ipchains?

Why are tables built into ipchains? What was the benefit of adding tables to ipchains? Is there a simple scenario that would illustrate how tables are used to increase performance or offer some other ...
4
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2answers
120 views

set connection limit via iptables

I want to limit the IP traffic of an application (AceStream Player). The problem is that I get disconnected, if too many IP connections are established. Does anyone know, how to use iptables to limit ...
4
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2answers
251 views

Redirecting loopback traffic through a router

For some tests purposes, I am running multiple socket-based applications on one machine and want to simulate "real" network conditions between them. I thought the simplest would be to redirect all ...
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4answers
6k views

Restrict bandwidth with DD-WRT

I have DD-WRT installed on my router and I would like to be able to restrict the bandwidth both up and down on a certain IP or Mac address. I am happy to get my hands dirty and use console. I am sure ...
4
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1answer
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Why does my firewall (iptables) interfere in my bridge (brctl)?

I set up a bridge br0 "attached" to two interfaces: eth0, my physical interface connected to the real LAN, vnet0, a KVM virtual interface (connected to a Windows VM). And I have this single ...
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2answers
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Did this tutorial block pings to my server?

I am a programmer teaching myself linux admin stuff. I followed this tutorial to setup a firewall on a VPS. As a part of that tutorial, I block all traffic except for web traffic and SSH traffic. I ...
4
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1answer
2k views

IPTABLES is slow after adding '-A INPUT -j DROP' to rule list

I am just getting started with iptables and stumbled across something I don't really understand. FYI, I followed the instructions of Ubuntu wiki's IptablesHowTo. The nat and mangle tables are empty, ...
4
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1answer
3k views

iptables: how to allow traffic from redirected port

I have a web service running on debian 7 and listening on port 8080. I want to redirect 80 to 8080 for inbound connections and allow only port 80. Here is my iptables configuration: root@localhost:~# ...
4
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2answers
245 views

Is it possible to set-up a VPN in such a way that I disconnect from the Internet if it goes down?

How can I set-up a VPN so I loose connection to the Internet if it goes down? I use Ubuntu and have used the network-dialog to use a VPN; but if the VPN goes down, it just switches to the non-VPN ...
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1answer
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tc on bridge port

I have a 4 port bridge: root@Linux-Switch:~# brctl show bridge name bridge id STP enabled interfaces br0 8000.000024cd2cb0 no eth0 eth1 ...