In computer networking, Network Address Translation (NAT) is the process of modifying IP address information in IPv4 headers while in transit across a traffic routing device.

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Linux as router with multiple internet providers

Linux as router: I have 3 Internet providers, each with its own modem. Provider1, which is gateway address 192.168.1.1 Connected to linux router eth1/192.168.1.2 Provider2, gateway address ...
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3answers
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iptables: The “script” way or the “*filter, rules, COMMIT” way?

I'm trying to figure out how NAT and iptables work. While I'm in the trial-and-error phase of learning about it, I found two somewhat conflicting howtos. One howto uses a script to call iptables ...
6
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1answer
124 views

Why doesn't NAT reserve ports from the machine's TCP and UDP port pool?

I made two experiments. This is the network for both of them: [private network] [public network] A -------------------- R ----------------- B 192.168.0.5 192.168.0.1|192.0.2.1 ...
4
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1answer
309 views

How to configure QoS per IP basis?

We have say 4 users in a private network connected to the Internet trough a Linux router with a public IP address that is doing network address translation (NAT). I gotta configure QoS to give access ...
4
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2answers
563 views

Send traffic to self over physical network on Ubuntu

I have a dual port ethernet NIC and let's say I have connected both ports in a loop and assigned the following IPs to the 2 ethernet interfaces: eth2 -> 192.168.2.1 eth3 -> 192.168.3.1 I want to ...
4
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1answer
5k 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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1answer
1k views

How to open VPN connection inside other VPN connection under Linux/Ubuntu

Is it possible to have two VPN connections on top of each other under Ubuntu? Scenario: My organization is quite large and has its own large network. Each group inside the organization has its own ...
4
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1answer
590 views

NetworkManager connection sharing doesn't seem to NAT packets

After setting up network sharing the easy way on the Ubuntu machine, and getting an IP address via DHCP on the Arch Linux machine downstream, the Arch machine is able to ssh to the Ubuntu machine and ...
3
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1answer
41 views

“ssh -L <port>” only working from local machine

I mean if I've got something like this: ssh -L 9000:itc.ua:80 andy@localhost It will open port 9000 on my local machine and when I hit http://localhost:9000 in Firefox it will forward to itc.ua:80 ...
3
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1answer
2k views

iptables: redirect local request with NAT

I'd like to redirect local requests to port which is translated with NAT. I have following rules: iptables -t nat -A PREROUTING -p tcp --dport 9020 -j DNAT --to 10.0.3.11:80 however request coming ...
3
votes
1answer
111 views

How to create an internal multipath gateway

Basically trying to bend bridging and NATing to my will with quite a unique project. I've simplified what I'm doing below (VM=Kali virtual machine for testing): ZoneX's are network namespaces, ...
3
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823 views

OpenVPN and routing problem on OpenWRT

My home topology: router1 (192.168.1.1) - D-Link dsl2540u server with static IP available from Internet (ADSL via ppoe). 4 LAN ports. router2 (192.168.1.2) - D-Link DIR-300 with OpenWRT. Plays ...
2
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2answers
368 views

Temporary redirect ports

I need a temporary redirection of some ports to another machine. I've tried: iptables -t nat -A PREROUTING -p tcp --dport 4321 -j DNAT --to-destination 192.168.121.4:80 But shorewall blocks all ...
2
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1answer
2k views

How does iptables MASQUERADE work on the incoming side?

I'm still reading the iptables manual page and other documents and digging around questions and their answers. This is the problem which arises. When we setup the NAT we use a POSTROUTING rule such ...
2
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3answers
549 views

Copying a file using SSH over a tunnel with cert forwarding

I need to find a way to copy files from mymachine to a server priv-server sitting on a private NATted network via a server pub-server with a public IP. The behind-NAT machine priv-server only has ...
2
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1answer
504 views

Can iptables be used to convert a single-homed host into a NAT server?

Given: I have a machine (HostA) with only one NIC which has Internet connectivity. I have another machine (HostB) with one NIC on the same switch. HostB is not configured for Internet access yet. ...
2
votes
1answer
178 views

Rewrite source IP in TCP replies using iptables

I'd like to rewrite the source IP on TCP/514 traffic leaving a redhat machine, for connections that weren't initiated from the machine. The machine receives TCP/514 traffic on an interface, for ...
2
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3answers
147 views

Bridge/Router with custom logic

I've a Linux box with 3 network adapaters, which I'd like to configure as follow: Adapter A is connected to computer A Adapter B is connected to computer B Adapter C is connected to the Internet. ...
2
votes
1answer
3k views

Sniffing VirtualBox machine behind NAT

I have a VirtualBox machine with a single interface connected to VB's NAT mode. What I would like to do is sniff all traffic coming from/to any machine behind that NAT. (I don't think I will need to ...
2
votes
1answer
48 views

Linux access point (airmon-ng/airmon-ng) not working

Background: I am trying to set up an access point on Linux. The ultimate aim is to run SSLStrip (for an exercise) so I need to be able to do something like this, to redirect port 80 traffic through ...
2
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0answers
68 views

1:1 Stateless NAT kernel version 3.16 or later using TC

I am trying 1:1 stateless NAT traffic. The traffic is coming in via a GRE tunnel and exiting via a VPN. I have done enough research to understand that traffic entering a linux box off of the GRE ...
2
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1answer
293 views

NAT box with multiple internal and external interfaces

Similar questions have been asked before but my setup is a little different and the solutions to those questions are not working. A have a CentOS 6 server running iptables with 5 interfaces: eth0: ...
2
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0answers
38 views

guest owns NIC, host and other guests access via NAT

OK, this is a bit complicated. On my host OS, when Guest1 is running, I want any incoming connections to go to guest1. So from the outside the system looks like guest1. But I still need to access ...
2
votes
1answer
69 views

(S/D)NAT over NF hooks

Could someone help on explaining the advantage of iptables NAT over the netfilter hooks. Say suppose, instead of using NAT if we create custom kernel module to bind handler with netfilter for PRE/POST ...
2
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0answers
95 views

Why isn't my nat-to not applied to the pass out rule?

I've a strange problem concerning NAT on an OpenBSD-Box with pf. I've cut down my pf.conf to the following lines: extif = "pcn0" intif = "pcn1" block drop all #Allow all incoming traffic from intif ...
2
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0answers
451 views

IPtables rule to double NAT [closed]

Let me rephrase it.. I just need an IPtable rule to do double NAT-ting.. Host A - Host B - Host C - Host D Host B should do both source NAT and destination NAT, so that my request from Host A ...
2
votes
1answer
593 views

iptables Port Forwarding — no service with the port

I have setup a network as in the image below: Firewall (FW) running CentOS 6 has two physical interfaces with subinterfaces: eth0:2 — 10.100.1.78/25 eth0:3 — 10.100.1.79/25 eth3 — 192.168.0.21/24 ...
2
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0answers
48 views

pf out interface?

I'm trying to figure out how to allow all hosts in $dmz to reach any host when egressing $extif. I can't seem to find the equivalence of netfilters "-o $extif", and I'd like to avoid specifically ...
2
votes
0answers
193 views

FreeBSD pf firewall, new connections severly delayed when nating

I have a newly setup fbsd 9.1 with pf, which itself doesn't experience any slowness when for example downloading a debian iso from my local debian repo (ftp.se.debian.org). Any machine behind it, ...
1
vote
1answer
140 views

ssh connection refused from same PC when going outside local network

I have sshd running on port 8000 running on a freshly installed plain vanilla Linux Mint 17.2 Rafaela. $ sudo netstat -tnlp | grep :8000 tcp 0 0 0.0.0.0:8000 0.0.0.0:* ...
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1answer
6k views

How to redirect to my squid proxy using iptables since DNAT target: only valid in nat table

I want to redirect the traffic in my lan network through squid proxy but I am having some problems with iptables rules. When I use the following rule: # iptables -I FORWARD -s ...
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2answers
369 views

FTP Troubleshooting

I have a centos 6.5 installed on Virtual Box. I'm trying to configure a basic ftp server. Below are details of it. Installed vsftpd from DVD/Yum: Status -> Successful Disabled firewall for test ...
1
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1answer
155 views

Does NAT allow accessing internal network (or router's local interface) from outisde by default?

I am using older SOHO router wl500gP (it is v1 but I think this is not important) with custom Oleg firmware. My topology looks like this: 192.168.3.3 192.168.3.2 NAT 192.168.2.1 ...
1
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1answer
673 views

How to forward one port to another (on the same machine)?

A machine (M) is behind a NAT. Port X is forwarded through, and available to the internet. My application wants to connect to port Y. How to I configure M to forward incoming data on port X to port ...
1
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1answer
219 views

How to enable ping between machines connected in two interfaces?

I have a linux board with two ethernet interfaces as mentioned below. eth0 connected to another linux machine (ad-hoc) eth0 on board 191.168.1.2 connected to Linux machine 192.168.1.3 eth1 on board ...
1
vote
1answer
403 views

Configure NAT filtring behavior with iptables

I'm using this rule to configure SNAT: iptables -t nat -A POSTROUTING -o eth1 -j SNAT --to-source 193.49.142.107:4000 I want to specify a rule to filter out packets not destined to the internal ...
1
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1answer
1k views

Randomize external port when doing NAT with iptables

I want to configure a NAT behavior different from the default one implemented by iptables. In this example: iptables -t nat -A POSTROUTING -o eth1 -j SNAT --to-source 193.49.142.107:2000-400 The ...
1
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1answer
420 views

Redirection to services in NAT or Bridged Network only with one subdomain

I have one subdomain (dyndns). xyz.dyndns.com (f.e.) Here my question begins: I have a server for virtualisation. On the server I have multiple VMs where different web-services are available ...
1
vote
1answer
64 views

Virtualbox - how to give Internet access and internal network access to two VMs?

I made two Virtualbox virtual machines, CentOS 7 latest iso. I gave them each 2 network interfaces, one NAT and one "Internal network" in order to get them to talk to each other and have Internet ...
1
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1answer
40 views

Access 2 VM's with one IPv4

I have two Virtual Machines. The 1st VM is running Debian 8.2 and the 2nd one is running Ubuntu Server 14.04.2 LTS Also I have one Public IPv4 The IPv4 assigns in only one server at a time. I assume ...
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1answer
525 views

GlusterFS how to failover (smartly) if a mounted Server is failed?

In GlusterFS, lets say i have 2 Nodes (Servers) on a Volume. Lets say the volume info is something like this: Volume Name: volume-www Brick1: gluster-server-01:/volume-www/brick Brick2: ...
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vote
1answer
104 views

linux nat different rules

eth0 (192.168.1.0/24) --> wan eth2 (192.168.10.0/24) --> lan0 I use these rules to enable NAT on my linux gateway: iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE iptables -A FORWARD -i ...
1
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1answer
98 views

Need help selecting networking option in VMware workstation

I am a complete noob in this area, so I really need help and advice. I am trying to setup something like a VPS on my computer. What I will do is: 1) Install vmware workstation on my computer 2) ...
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1answer
68 views

Network translation, one to one, not one to many

Desired scenario: a small subnetwork of Linux machines, all accessible through another Linux machine (acting as an IP router). These machines would be pre-configured with addresses on a private ...
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24 views

Changing the port letsencrypt tries to connect on

So, one of my servers is behind NAT, and since there is already a publicly accessible apache server going on my LAN, I decided to access it from the outside with different ports, and remap them to the ...
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0answers
28 views

Alter DST port on bridged traffic

I need to rewrite the UDP destination port on traffic which is only bridged/L2, but I could not match this traffic via iptables. This traffic isn't going through NAT chains (it could be matched in ...
1
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1answer
29 views

1:1 NAT through VM VPN

I've got a few client servers that I connect to with different VPN clients (e.g. Cisco, OpenVPN, etc). I'm trying to set up an Ubuntu 14 VM (with VPN client permanently connected) for each server to ...
1
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1answer
45 views

iptables DNAT+SNAT: unwanted multiplication of the same udp datagram (and malfunction)

trying to figure out my mistake in the following very simple scenario: |peerA|(Aip:Aport) <--> (Bdev:Bip:Bport)|NatNode|(Cdev:Cip:Cport) <--> (Dip:Dport)| peerD (peer A emits datagrams ...
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25 views

Forward public network around current network

For the purposes of this discussion, I have a very current always-on linux machine with two nics: wifi0 eth0 A very crude diagram of my desired configuration looks like this: ...
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1answer
136 views

How check a port forwarded from localhost to localhost on.. localhost?

I'm learning about iptables, firewalling, routing and so on. I'm on Linux, Centos7, and I've set up a local port forwarding to localhost with: firewall-cmd ...