CentOS 5 Networking :: IP Forwarding Is Not Working
Apr 1, 2009
I'm trying to set up my CentOS 5 box as a gateway for my home network.I've set up dhcp on my internet interface (eth0) and dhcpd on my LAN interface (eth1).I can browse the internet from my CentOS 5 box.I can ping the CentOS 5 box from my LAN.However, I can't browse the internet from my LAN.I've enabled IP forwarding in /etc/sysctl.conf and I've disabled my firewall. I've saved these changes and rebooted. Again, no internet browsing from my LAN.
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Jan 18, 2010
I am setting up a new server with 2 nics installed. Nic0 goes to the firewall and nic1 goes to the internal engineering network.
Problem is Ip forwarding is not working!
Particulars:
Server Name - slick
Firewall Name - gateone
engineering node - crooked
Routing on slick:
From crooked ( which is inside the server (slick) with an ip address of xx.xx.221.249 the only way I can ping or anything outside of the firewall ( gateone) is to turn on IPtables with this configuration:
I don't want to use IPtables. I need the ip forwarding to work.
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Aug 31, 2009
Can anyone here point me to a walk-through or discussion of how to use Webmin to set up port forwarding/NAT on a dual-NIC Centos 5.3 box? The layout will be simple:
Internet --- NIC1 [CentOS Box] NIC2 --- Switch to other PCs
We have a BUNCH of exposed services that are on special ports -- for example, to connect to one machine, you go in with [IP_Address]:12000, and to connect to another, [IP_Address]:12002, etc., etc. We're currently using OpenSuse 10.3 on this box, and YaST makes this criminally easy (you give it the incoming port number and the destination IP/port numbers and it just works). But OpenSuse 10.3 is nearing EOL, we're buying a new machine, and I'd like to use CentOS on the new one.
I've read the sparse Webmin documentation in their Wiki, and it leads one to believe that you simply insert a "NAT" rule. But there's obviously something they're leaving out. I *am* opening the ports in the firewall. But when I log in to [IP_Address]:port, it just times out. The port forwarding never occurs. The test in this case is SSH, and I know that SSHD is working properly because I can log into that machine just fine from another PC on the same internal subnet.
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May 7, 2011
I am trying to redirect my display from a debian box that I ssh into to my laptop. I connect using
Code:
$ssh -vv -XC remote.host
and in the debug messages all I get about X is this
Code:
debug1: Requesting X11 forwarding with authentication spoofing.
Once I'm connected, X forwarding does not work. For example, when I try and start, say, xcalc, I get
Code:
$xcalc &
Error: Can't open display:
It seems that the problem is the $DISPLAY variable is not set on the remote machine (echo $DISPLAY doesn't return anything), but from what I read, sshd is responsible for setting this variable, as long as "X11Forwarding yes" is uncommented in the /etc/ssh/sshd_config file (which I made sure is true). Is there any other reason why sshd won't open a display on the remote host?
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Apr 23, 2009
I am running Fedora Core 10 and KDE 4.2.1. My KTorrent is having trouble finding online peers lately. I suspect this is a port forwarding issue. I have set up my router to forward port 4444 (UDP) and port 56000 and more (TCP) to my machine's IP address. I have also set my local firewall (system-config-firewall) to allow these ports through.But when I try to test ports 4444 and 56000 via this Open Port Check Tool, it tells me they are closed
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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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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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Dec 30, 2010
I have just recently switched my setup to have my server be in the middle of traffic and act as my new router while making my other routers just switches. However, after doing this I can no longer access my UPnP devices. They used to show up in my router but I am assuming either there is an issue with my iptables rules or that some how having my server run the dhcp and dns routing is messing with UPnP.
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Mar 26, 2009
I'm running Centos 2.6.18-53.1.13.el5 in a VM. Currently I'm studying for my RHCT.I'm trying to enable IP forwarding so I edited this line in the /etc/sysctl.conf:
# Controls IP packet forwarding
net.ipv4.ip_forward = 1
Then I ran sysctl -p
[code]....
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Aug 11, 2011
i am forwarding HTTP request to a internal server, it is quiet successful but access logs donot show the ip of the external m/c. Rather it shows the ip of the machine on which i have enabled port forwarding.
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Nov 30, 2009
I have recently installed Centos 5.4 on a server with 3 network cards. I am trying to enable IP forwarding which has been successful by executing the following command:
echo 1 > /proc/sys/net/ipv4/ip_forward
I tried to make this permanent by adding net.ipv4.conf.default.forwarding=1 to the /etc/sysctl.conf file.
When I restart the network service I get the following code...
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Dec 12, 2009
I have just set up shorewall on my router running Arch Linux. The external network is on eth0 and the internal network on eth1.I have set it up for masquerading and that works fine and I can open ports to the firewall. But I'm having trouble with port forwarding to my internal machines.The problem I have is that when port 22350 is forwarded to 192.168.1.3 on my local network, checking the port with nmap from a remote computer gives me:
Code:
PORT STATE SERVICE
22350/tcp closed unknown
[code]....
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Mar 5, 2011
I did local apache server at internal ip 192.168.1.2 and i wanna to do port forwarding to enter to it by my external ip address ?
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Jul 20, 2011
I installed CentOS. NetworkManager successfully installed and launched. I can ping any IP from terminal but I can't open any site in browser except 127.0.0.1 I can't open IP of the modem 192.168.1.1 in browser also.
The results of some commands:
ifconfig
eth0Link encap: EthernetHWaddr 7D:60:00:00:00:00
inet addr: 192.168.1.5Bcast: 192.168.1.255Mask:255.255.255.0
inet6 addr: fe80::7f60:ff:fe00:0/64Scope:Link
[Code]....
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May 19, 2011
I am running opensuse11.4. When trying to forward emails I can only do so as attachment. When I click and hold to select the forward inline option I get an empty email - same as if I would have clicked new. The same happens when I place the inline button on to the toolbar. Is this a bug with Kmail or is there another setting to forward mail inline?
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Jan 6, 2010
Pre-exsisting issue from 9.04 server, and has never worked right for me. When I try to open an X11 forwarded app on a mac using the command "ssh -X myusername@serverIP" Other linux machines have similar issues from terminal. I can login just fine and preform any actions I want that do not require X11 forwarding, like say firefox or a manager. I just get the error "Error: no display specified" when trying to do anything with X11 forwarding. I have almost no Linux experience but from tinkering and my friends tinkering wonder if I have a x authority issue.
At one point I had ubuntu desktop package installed (forwarding still did not work then), did a unclean uninstall of it installed Xubuntu. Xubuntu did nothing but throw fits saying I did not have authority to preform all sorts of actions, many relating to root access. This box is meant to be a headless file, print and web server with the ability to login remotely as a convince for administration. I have given up on having a working GUI of any kind on this box. I really do not want to reinstall because of the amount of data on the main partition. What can I start trying to look into?
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Dec 20, 2010
Got Ubuntu Server 10.10 installed as a virtual machine (vmware). When i forward X through SSH (putty) i can start xeyes, xcalc,etc.
Now when i disable ipv6 putty can't set the display variable and i get "Error: can't open display". I haven't changed anything in putty or win 7 (the host system).
I disable ipv6 by putting these lines in /etc/sysctl.conf
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
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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 25, 2010
I was able to do on Debian and Ubuntu Servers X applications running on remote servers where I was able to login via SSH. Tried the same with CentOS did not worked. in /etc/ssh/sshd_config
[Code]....
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May 17, 2011
I have two SUSE(2.6) virtual machines running in the same subnet with two network cards each as shown below.
VM1------------------------------------------------------------------------------
appstage1:~ # ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:22:5A:24
inet addr:192.168.128.12 Bcast:192.168.128.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe22:5a24/64 Scope:Link
[Code]....
Ultimately my DB will run in VM2 and any DB requests coming in at 2055 of VM1 should be forwarded to port 2055 of VM2. Since I do not yet have a DB running I am trying to test with netcat.
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Apr 13, 2009
I installed CentOS 5.3 on my Shuttle SS-31T with SiS 190 network adapter. While booting the message "Bringing up eth 0 [ OK ]" appears. After booting it isn't possible to surf to an internet location (p.a. www.google.com). It's also impossible to ping other machines in the network. After typing ifconfig everything seems to be ok.
ipv6 is turned off
IP : 192.168.0.3
Subnet : 255.255.255.0
Gateway : 192.168.0.1
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Nov 20, 2010
I have a Centos 5 server on my LAN for testing the websites that i develop.It worked perfectly until this morning , after cold start -up, it seems that my network card is not enabled . Everything works normal:gui and terminal but no internet access. I'll run some commands on my Linux box and write the results , by hand , to this forum .
* uname -r : Linux Server 2.6.18-194.26.1.el5 i686 i386
* ifconfig eht0 : eth0 : error fetching interface information
* ifconfig -a : I get only results for loopback (lo)
* less /etc/modprobe.conf : alias eth0 sis900
* lspci |grep -i eth : 00:04.0 Ethernet controller :Silicon Integrated Systems [SiS] sis900 PCI Fast Ethernet (rev 90)
[Code]...
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Nov 24, 2009
My X crashes when I...
1) ssh to a remote centos server using X11 forwarding
2) open the virt-manager remote application (the virtualization management app)
3) Open the remote console
Just to be clear, my local X11 crashes. I get back to the log in screen.
I get in my Xorg log:
Backtrace:
Fatal server error:
-Is this enough for a bug report?
-How I can make X dump a core file for better debugging?
-Do -debug RPM packages still exist, and if so, should I install one for the X server and will this help with debugging, and if so, how do I install it.
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May 7, 2011
I've had Debian on my laptop for around 4 months which I rarely use. I'm using Squeeze since it seems to be the only release that will work with my ethernet card.The internet had been working fine for a couple of months but broke when I tried to allow port forwarding for torrents. I could only connect to the internet after this by using:
iptables -F
iptables -X
iptables -t nat -F
[code]....
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Feb 17, 2009
I have hp dv6291 laptop with Centos 5.2 os the NIC & WLAN not working ?
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Jul 16, 2011
I can't get the CentOS version of pptpd to work. I have a Debian 6 one with the exact same setup that does work. The required port is open according to various external port checking websites. It's giving me random errors when trying to connect, including 800, 809, 619. This is what I did so far;
Step 1. Installing pptpd the pptpd is the daemon that runs the pptp server.
To install this:
Step2. Next you will need to modify the pptpd.conf
Step 3. The vpn server is now configured and now you must setup authenticated users:
Step 4. When pptpd was installed it started automatically so we will need to restart it to apply the changes:
Now, if you would like to add internet access over this vpn, you can do this:
And find the line for ipv4 forwarding and make sure it = 1:
Then use iptables to get the net forwarded:
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Jun 2, 2010
We have on Ubuntu 10.04 LTS installed on one m/c which is connected to office network using pptp vpn.Now i want to enable ip-forwarding on this m/c so that i can connect my RH9 m/c through this. For enabling ip forwarding i did the basic thing "echo "1">/proc/sys/net/ipv4/ip_forward" And added route on the RH m/c as route add -net 10.254.254.0 netmask 255.255.255.0 gw 192.168.1.10 dev eth0" (IP of Ubuntu m/c is "192.168.1.10 and RH m/c is 192.168.1.15) But some how ip-forwarding is not working properly.
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Apr 5, 2011
I'm facing a challenge in setting up a simple routing between 2 networks. The situation is as follows.We're using 2 networks, 1 that handles all the office traffic and 1 that is used for storage traffic to the NAS. I'm trying to setup a simple router that will forward requests from the office LAN to the storage one, so people can access the NAS interface on the storage LAN.
So, I have a CentOS 5.5 box, connected to both networks that should handle this job. The office LAN is 172.29.38.0/24 and the storage LAN 10.1.2.0/24. IP adrresses of the linux box are 172.29.38.98 (eth0) and 10.1.2.98 (eth1).First I started by enabling IP-forwarding in the kernel:
Code:
# cat /proc/sys/net/ipv4/ip_forward
Below is a copy of the iptables in use:
Code:
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
[code]....
It just never seems to get to the machine on the other side. I've verified that I can access both networks from the router and I can ping the router from my client.
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