iptables allow creation of rules to define packet filtering behavior.

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Have someone ever audited the default OpenWrt firewall rules?

I have an Openwrt 10.03.1 installed from: openwrt-ar71xx-wrt160nl-squashfs-factory.bin (firewall only customized with this: sed 's/REJECT/DROP/g' /etc/config/firewall) - so besides this, IT'S A ...
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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 ...
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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 ...
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Move iptables rule (w/o removing and adding)

Is there a way to move a rule in the iptables and change it position ? I'm aware i can use -I to insert a rule in a specific position, but i also like to keep the counters.
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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 ...
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436 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 ...
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159 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 ...
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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 ...
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71 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 ...
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143 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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iptables to block https websites

I wish to block a few websites that also run upon https, like facebook, twitter, and gmail, in my organization. Squid is not supposed to be used here as per the orders from higher management. We can ...
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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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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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439 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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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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361 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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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 ...
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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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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 ...
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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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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 ...
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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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How can I redirect outbound traffic to port 80 using iptables locally?

I'm trying to locally redirect ports on my Ubuntu machine using iptables. Similar to transparent proxying. I want to catch anything trying to leave my system on port 80 and redirect it to a remote ...
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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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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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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 ...
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Having Linux port remap to itself

I have a scenario: I have 4 server and 3 web inbound requests that I have to allow through a modem/router. the ports are https(ssl)443 ssh22 and http80. All 4 servers want them. I had set up the ...
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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 ...
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IPTables and transparent proxies

I have set up a local, transparent TCP proxy on localhost. I want to redirect ALL TCP traffic to this proxy, so it can handle it and nothing "leaks out," circumventing the proxy. I need to use ...
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Debian Wheezy subnet configuration (proxy, MASQUARADing etc.)

I have a "server" with eth1 having a full IP address, DNS, gateway and proxy name connected to the university internet/intranet provider and eth0 IP 192.168.1.2 connected by a gigabit switch with two ...
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How can I prevent iptables from counting bytes and packets on empty chains?

Background I occasionally have firewall rules that I need to use for maintenance windows, but don't want active (and therefore consuming CPU cycles or slowing the network interface) the rest of the ...
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How do you do NAT port redirection with PF?

In Linux, you can do NAT port redirection with a command like this: iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8000 What is the equivalent with BSD's PF?
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fail2ban log parsing too slow on Raspberry Pi - options?

I'm running fail2ban on a Raspberry Pi at 950MHz which I cannot overclock further. The Pi is occasionally subject to SYN floods on particular ports. I've set up iptables to throttle the rate of SYNs ...
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iptables port forwarding

I have a CentOS server with Java/J2EE(Tomcat) installed on TCP port 8080. I have two interfaces, eth0 and lo. I need to forward all incoming connection on TCP port 80 to 8080. I tried doing the ...
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How can I redirect all traffic except local through external proxy with iptables in dd-wrt?

I have a router with dd-wrt. I have a firewall running to direct all traffic through an external proxy. It works great except that it also redirects local Ips and my proxy does not allow Ips, so I can ...
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iptables change log

Somehow an iptables rule was added to one of my systems. Does (or can) iptables keep a log about when and (maybe) who made a rule change? If iptables itself can't, is there a wrapper that might do ...
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397 views

NAT with transparent proxy

is there a way to redirect all non local http requests that through my computer to use my transparent proxy, so i can log all websites are they visiting? and if possible all https requests too.. my ...
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Screen session running as root? (it shouldn't be) node.js

cd /serv screen -R node {in the screen} node test.js C^a d initially, ls -l /dev/pts total 0 crw--w---- 1 tick-tock tty 136, 0 2011-04-19 16:41 0 crw--w---- 1 tick-tock tty 136, ...
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multigateway routing for specific src port

I have two gateway to access internet, somehow I want to load balancing it, so far its working, but some connection or service need persistent gateway IP to be used, so the client should never change ...
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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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Is there any difference between these two configuration options?

Is there any actual difference between iptables -P FORWARD DROP and net.ipv4.ip_forward = 0 ? I know that one is a firewall command while the other one is a kernel option. But: I don't know ...
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Port fowarding and load balancer in ubuntu server 12.04

I am looking to create a load balancing server. Essentially here is what I want to do: I have a public IP address, lets say 1.1.1.1 I have a second public IP address, lets say 2.2.2.2. I have a ...
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321 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). ...
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Undo iptables modification

I ran the following iptables commands to create a blacklist rule but used the wrong port: iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set --name SSH iptables -A INPUT -p tcp ...
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Does iptables -F permanently delete all iptables rules?

In a RHEL training document, the author says: ...run the following command to disable the firewall on the current system: iptables -F He explicitly uses the word "disable" which to me suggests ...
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iptables multiple -d flags not allowed

I am trying to log all my outbound connections to a file using iptables. This is my rule: -A OUTPUT ! -o lo ! --destination 127.0.0.1 -m state --state NEW -j LOG --log-prefix "new_connection " ...
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iptables does not list rules i have created

I'm using this guide to set-up a shared internet connection between two PC's. At step 8 it says I should run the commands: iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE /etc/rc.d/iptables ...
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Meaning of log entries from an iptables configuration

My router has Linux as its OS. The system log has a lot of rows about iptable and klogd that I don't understand, could someone explain them to me? The iptables setup: iptables -t nat -A PREROUTING ...
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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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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 ...