Networking :: Iptables Postrouting SNAT Not Working?
Aug 9, 2009
trying to alter the source IP of my outgoing http packets through iptables. This should be simple enough, right? Regardless, I'm cracking my head trying to understand what I am doing wrong. Wireshark shows that the outgoing packets do not have the source IP modified at all. I want this to happen for TCP packets sent on Port 80 (http traffic). I am using the nat table in iptables to attempt POSTROUTING. I've tried several different rules at separate times:
iptables -t nat -A POSTROUTING -p tcp --dport 80 -j SNAT --to-source 172.16.8.50 <--- Still sends out TCP packets as originating from 172.16.8.100
iptables -t nat -A POSTROUTING -s 172.16.8.100 -p tcp --sport 80 -o eth0 -j SNAT --to-source 172.16.8.50:80 <--- Still sends out TCP packets as originating from 172.16.8.100
iptables -t nat -A POSTROUTING -d 172.16.10.71 -j SNAT --to-source 172.16.8.50 <--- This rule was a last-ditch effort. It is supposed to rewrite the source IP for ALL packets going to the single client machine. Still doesn't work - the packets have the source IP unchanged.
I have another server - let's call it serverB/172.16.8.50 - that forwards all http TCP packets on port 80 to serverA/172.16.8.100. This part works. But when ServerA responds, it responds with its source IP for ServerA. I need it to respond with the source IP of ServerB. Otherwise, the client gets confused and ignores the packets (because the client sent an HTTP request to ServerB, but the response comes from ServerA).
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Sep 29, 2009
i want to open specific port using iptables i.e 3159 Whenever i tried to telnet it generates the following error
Code:
# telnet 172.16.4.100 3195
Trying 172.16.4.100...
telnet: connect to address 172.16.4.100: No route to host
telnet: Unable to connect to remote host: No route to host
but when I stopped iptables
Code:
# service iptables stop
Its working fine
i added the ports in iptables i.e.
Code:
#iptables -A INPUT -p tcp --dport 3195 -j ACCEPT
for safe side I also added telnet port
Code:
# iptables -A INPUT -p tcp --dport 23 -j ACCEPT
but result was same.... In short telnet works without iptables but with iptables it generates the error mentioned above
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Jun 10, 2009
I have an old iptables script (?) that I got from iptablesrocks.org, which works fine with my antique Fedora 4 system. I transferred it to a brand new RHEL 5.3 install, but when I go to use 'iptables-restore < firewall_script' it throws a 'no command specified' error at the very last line of the script, which I have never seen before. The script works fine on Fedora 10 and RHEL 5.1, I am pretty sure it even works fine on RHEL 5.2. Could it be that the fact that I am using 64-bit Linux for the first time, and need to do something different? Here is the script: [URL]
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Jun 20, 2010
On the computer on which I have to login, Shoreline is installed.I know I can add rule to /etc/shoreline/rules but I decided to manually enter an iptable rule by typing:
Quote:
/sbin/iptables -A local2fw -s 10.100.98.74 -p tcp -m tcp --dport 22 -j ACCEPT
Then why am I not able to login using 10.100.98.74... I get connection refused error...
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Jan 28, 2011
I've used iptables since it replace ipchains, and I've never had a problem like this.The problem is, as you can see by the title, that port forwarding simply does not work.
network topology:
Slackware Linux Server:
eth0 - LAN (192.168.0.0/25)
eth1 - DSL Static IP
eth2 - cable Static IP
eth1 is our standard office connection; it handles all of our default traffic (web browsing for the staff, email, etc). eth2 is our VPN connection, as well as use for all incoming connections (www, etc). Behind the linux box I have a series of Windows Server 2008 R2 boxes that are used to run our office software, website, etc - I don't care how nice they make their products these days, I simply don't trust any MS box open to the net.
Therefore, this leaves me with having to port forward port 80 from eth2 to the internal IP address of the web server.
My ruleset is as follows:
$WWW - ip address of the web server
iptables -A FORWARD -d $WWW -p tcp --dport 80 -j ACCEPT
iptables -t nat -A PREROUTING -i eth2 -p tcp --dport 80 -j DNAT --to $WWW
Running ip route shows that I have routing entries for all 3 networks, and I can ping, ssh, etc to any of the addresses without issue. OpenVPN connects across eth2 as well, and all 15 of my VPN tunnels work fine. However - and here's the kicker - if I delete the default route and replace it with the route for eth2, port forwarding works fine.
If we accept that my networks are as follows:
192.168.0.0/25 - eth0 net, gw .1
1.1.1.0/29 - eth1 net, gw .1, eth1 ip .2
2.2.2.0/30 - eth2 net, gw .1, eth2 ip .2
then ip route reveals the following:
2.2.2.0 via 2.2.2.1 dev eth2
2.2.2.0 dev eth2 scope link src 2.2.2.2
1.1.1.0 dev eth1 scope link src 1.1.1.2
[code]....
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Jan 18, 2011
I am using putty in my windows machine to access my Linux server terminal.
Code:
Putty works fine if I disable my Linux IPTABLES. My Windows machine IP is 192.168.1.249
Linux server IP address is 192.168.1.200 I don't know how to allow it through IPTABLES.The port which putty is using is 22.
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Sep 12, 2009
For the background, I'll be using my router as a firewall with snort-inline enabled. I got 3 NIC's: one for the WAN, the second will be bridged to the WAN NIC for queuing traffic which snort-inline requires, and the third is the LAN NIC (the computer I use for everyday work). Here's how I have my interfaces set up:
Code:
# /etc/network/interfaces
# Loopback interface
auto lo
iface lo inet loopback
[code]....
From what I understand, queuing needs to be set up on the bridge. From the documentation I've read it's done like this:
Code:
iptables -A INPUT -j QUEUE
And then to forward traffic, I did:
Code:
iptables -t nat -A POSTROUTING -o br0 -j MASQUERADE
I've done this and am able to ping the router, obtain a DNS address from dnsmasq from the LAN computer. From the router I am able to connect to the internet (ping, links <address>...). From the LAN computer trafficking isn't getting forwarded, Firefox, links, ping all don't resolve.
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Feb 18, 2010
I was trying to setup port forwarding on my setup. My network consists of:
Code:
[Server: xxx.xxx.xxx.15]
|
|
[ switch ]
[code]....
I ran the following 2 commands:
# iptables -t nat -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j DNAT --to-destination xxx.xxx.xxx.15:80
# iptables -A INPUT -i eth1 -p tcp -m tcp --dport 80 -j ACCEPT
Yet I am unable to connect. Are these the correct commands? I am using IP Masquedering on the same box using the following commands:
Code:
$IPTABLES -P INPUT ACCEPT
$IPTABLES -F INPUT
$IPTABLES -P OUTPUT ACCEPT
[code]....
I don't think there is a hidden firewall in the switch but if these commands are correct, then I may need to contact my ISP and see if they are blocking the commands. I just wanted to make sure I was not doing some stupid mistake before I try to contact my ISP.
EDIT: Also, is it possible to forward Port 80 requests to different servers depending on the hostname used to connect, so say [URL] redirects to server xxx.xxx.xxx.15 while hhh.com redirects to xxx.xxx.xxx.16?
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Sep 28, 2010
I have managed to get iodine working between my ubuntu intrepid box and my windows client with a caveat.
The firewall rules allows DNS queries inbound. The client tunnel endpoint gets assigned an IP address and the tunnel is established properly.
However when I try to ping from the client machine, the reply packets are not coming back.
I used TCPDUMP on the Ubuntu box and watch the dns0 tunnel interface, and noticed that the packets are reaching the Ubuntu box from the client, but I don't see ANY ICMP echo replies until I turn off the firewall from Firestarter.
I see that outbound access rule is to allow all.
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Jan 27, 2010
I'm running on RHEL 5.I have a PREROUTING rule that redirects port 443 to port 8443. If I do "iptables --list" or "iptables -v --list" I see only the standard chains listed. As the prerouting rule is the only rule I have, it appears that I don't have any rules. Is there a way to do a full and true listing of all rules other than "iptables-save"? You might just as well read the iptables file.
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Jun 27, 2010
When I try to run anything that uses iptables, even just iptables -L, I get:
Code:
1+drm33.2/modules.dep: No such file or directory
iptables v1.4.4: can't initialize iptables table `filter': iptables who? (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded. This is on a fresh Ubuntu minimal install, using my VPS hosts image (so they could have messed something up). I know there have been issues in the past with iptables on Ubuntu on xen. Is this a Ubuntu bug? Is there a solution?
incidentally depmod -a gives:
Code:
WARNING: Couldn't open directory /lib/modules/2.6.32.11+drm33.2: No such file or directory
FATAL: Could not open /lib/modules/2.6.32.11+drm33.2/modules.dep.temp for writing: No such file or directory
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Apr 12, 2009
I am facing a problem when I tried to set policies on the firewall with following commands:
iptables -A INPUT -p TCP -s 0/0 --dport 53 -j ACCEPT
iptables -A INPUT -p UDP -s 0/0 --dport 53 -j ACCEPT
iptables -A INPUT -p TCP -s 0/0 -j REJECT
[code]....
Here, I want to deny all traffic except DNS traffic, it should be permitted. I tried to log the traffic but I did not find any update in /var/log/messages.
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Jun 11, 2010
see many threads / websites about how to configure iptables. They say if you use these
rules it will allow http traffic. But they don't work. I like to deny all then allow specific ports open for traffic.So far I tried the script to flush and update my iptables rules, trying to open port 80 and 53 for http and DNS traffic:(I made the script executable, with $ iptables -L -v I can see that the rules are changed after I run the script. )
Code:
#! /bin/bash
iptables -P INPUT DROP
[code]...
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Mar 26, 2010
I have the following setup and Im trying to forward all incoming connection on port 1194 on eth2 which is the external network to ip 192.168.10.100, but seems its not working.
Current config:
# Generated by iptables-save v1.3.8 on Sun Nov 16 00:00:54 2008
*nat
:PREROUTING ACCEPT [26751696:2175544875]
:POSTROUTING ACCEPT [339911:19096812]
[code]....
plus im adding the prerouting:
iptables -t nat -A PREROUTING -i eth2 -p tcp --dport 1194 -j DNAT --to-destination 192.168.10.100
This configuration doesnt work. I also I have tried:
iptables -D PREROUTING -t nat -p tcp -d XX.XX.XX.XX --dport 1194 -m state --state NEW,ESTABLISHED,RELATED -j DNAT --to 192.168.10.100:1194
and the same its not working. Connecting thru telnet to the domain: telnet mydomain.org 1194 doesnt work, but within the server, running telnet 192.168.10.100 1194 it works.
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Jul 17, 2009
I am using ubuntu 8.40 as a router wit 2 nic.eth0 is for local and eth1 is for external network.i have a internal webserver in my lan and want to forward some ports to the net and i executed te following commands.
iptables -t nat -A PREROUTING -p tcp -i eth1 -d 192.168.0.239 --dport 8080 -j DNAT --to 192.168.10.99:8080
iptables -A FORWARD -p tcp -i eth1 -d 192.168.10.99 --dport 8080 -j ACCEPT
But i cant connect to the port 8080 from the external network.
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May 14, 2011
I'm trying to limit the number of the ICMP packets reaching my server, so I'm using the limit module of iptables, unfortunately it seems the limit I set is totally ignored as I can easily send tens of ICMP packets and get a reply in less than 0.3 second Quote:
m3xican@m3xtop:~$ sudo ping -i0 -c20 x.x.x.x 20 packets transmitted, 20 received, 0% packet loss, time 230ms
rtt min/avg/max/mdev = 184.969/185.895/189.732/1.301 ms, pipe 16, ipg/ewma 12.138/186.232 ms This is the rule I'm using to accept ICMP packets (default setting is DROP)
Code:
iptables -A INPUT -p icmp -m limit --limit 1/s -j ACCEPT
And these are the kernel modules related to iptables
Code:
Module Size Used by
xt_limit 1382 0
[Code]...
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Jun 30, 2009
i have just setup a firewall using iptables on centos 5.3 but there's an issue with ftp
i can connect and i can login when i give command "ls" it says entering passive mode
and afterwards it times out do you know why? i have port 21 open in my firewall but still....
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Oct 8, 2010
I have an ubuntu server virtual machine with a webhost. I am trying to configure the firewall. I am having a problem with sendmail and the required firewall configuraiton If I type the command:
iptables -F
Then sendmail works perfectly. I can see the emails sent in my googlemail inbox. I then configure my firewall as follows:
iptables -F
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -p tcp --dport 2252 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j ACCEPT
[Code]....
(I have moved SSH to a diffrent port) Once this is setup sendmail no longer works. I had assumed that sendmail will establish a tcp connection and the first rule will allow all established connections to pass. why this iptables/netfilter config stops sendmail from working.
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Nov 26, 2010
I am unable to restore my iptables from iptables-save after upgrading Fedora. I cannot get iptables-restore to work, and I have resorted to entering rules manually using the GUI.
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Sep 17, 2010
I am facing a strange problem witht my iptables as there are some firewall entries stored somewhere which is displaying the below firewall entries even after flushing the iptables & when I restart the iptables service then the firewall entries are again shown in my iptables as shown below,
[root@myhome ~]# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
[code]....
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Nov 3, 2010
I recently installed a new Ubuntu PC that runs iptables and PSAD. I had the same script on another Ubuntu PC, but when I copied the script onto the new PC, I got this error. I don't remember where I found the tutorial for this, all I know is that this is the script (Edited for my usage):
Code:
#!/bin/bash
# Script to check important ports on remote webserver
# Copyright (c) 2009 blogama.org
# This script is licensed under GNU GPL version 2.0 or above
[code]....
Safe.txt contains:
Code:
127.0.0.1
192.168.1.8
192.168.1.1
98.200.58.73
192.168.0.1
And the error message generated is:
Code:
root@NETWORK-SERVER:/var/ddosprotect# ./ipblock.sh
' not found.4.4: host/network `127.0.0.1
Try `iptables -h' or 'iptables --help' for more information.
' not found.4.4: host/network `192.168.1.8
[code]....
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Jul 17, 2010
IPtables creates an error during startup as well as when I try to restart it: Here's the output of:
[Code]....
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Apr 16, 2011
I am running Ubuntu server 10.10 and trying to setup iptables rules in /etc/if-up.d/iptables
Quote:
root@host# cat /etc/network/if-up.d/iptables
#!/bin/sh -e
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
Problem is that iptables doesn't get updated and I don't see them when iptables -L is executed after reboot.
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Apr 28, 2009
To expand: I'm trying to set up a box with l7-filter, and I need to patch and compile iptables 1.4.1.1 as part of the process. I ./configured it with the prefix= argument so it would install into /sbin instead of /usr/sbin, and I did a yum remove iptables before installing it so as not to get in the way of the original iptables, but I'm wondering if this is really necessary - it's kind of annoying, because removing the original iptables removes the init.d script, deregisters the service, etc. If I don't, is it possible that iptables 1.4.1.1 might get overwritten in a system update or something, or will yum see that I've got a custom/newer version in there and leave it be?
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Feb 5, 2010
Iptables manual page says:
Why doesn't it make sense for packets coming from a wireless interface?
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May 7, 2010
I have set up OpenVPN for my connection. I'm using this to connect to the internet from different locations using tunnelling.
Right now I have a few IP's : on eth0 I have IP from my ISP, on eth0:1 I have my own IP.I set up MASQUERADE to eth0 - but in this case when I try to access my restricted resources IP address from ISP is visible.
What I want is to use my own IP address from eth0:1 - could somebody help me to build good working redirect entry for that? I want to redirect all connections to that IP assigned on eth0:1... - just to access Internet using my IP.
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Nov 11, 2010
How can I add ip address which is multiple of 3 and to 255? That is I want to block ip address which is coming from multiple of 3 to 255.
As an example 192.168.0.3,192.168.0.6,192.168.0.9,192.168.0.12 etc.
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Mar 2, 2010
how to allow a specific hostname with specific ports in iptables?
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Apr 24, 2011
We are stuck big time with IP forwarding where we have to use IP tables. Any advice will be appreciated.
Setup
Machine A --> Machine B -->Machine C
- Machine A connects with Machine B on "internal network"
- Machine B has 2 NIC (and two IP address) , one connected to Machine A (internal network) and one connected to Machine C (External Network)
We need all traffic coming from Machine A which flows to Machine B on port 60 to be directed/forwaded to Machine C (port 60).
Not allowed to configure Machine B as a gateway . Things work with rinetd program when we do a tcp redirect from Machine B port 60 to Machine C (port 60).
But just unable to make it work with IP tables rules. We tried following,but in vain
iptables -t nat -A PREROUTING -s Machine_A -d Machine_C -p tcp --dport 60 -j DNAT --to-destination Machine_C .6:60
/sbin/iptables -A FORWARD -i Machine_B -o Machine_C -p tcp --dport 60 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
Any valued inputs?
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Jul 26, 2010
pc need download file from internet ftp server, but can't now, how set iptables ?
iptables mod
[root@ad ~]# lsmod |grep ip
ip_nat_ftp 7361 0
ip_conntrack_ftp 11569 1 ip_nat_ftp
[code]....
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