In computer networking, network address translation (NAT) is the process of modifying network address information in datagram (IP) packet headers while in transit across a traffic routing device for the purpose of remapping one IP address space into another.

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32
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7answers
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How many computers can have the same public IP?

I've got a list of hundreds of page requests from the same IP and I need to know if these could be requests by different computers.
31
votes
5answers
2k views

Will everyone having Globally Accessible IP's in IPv6 be kind of a security nightmare? [duplicate]

Possible Duplicate: Switch to IPv6 and get rid of NAT? Are you kidding? I'm thinking about the way that in IPv4 most of the time you have a single point to configure a firewall on, mainly your ...
29
votes
8answers
24k views

Loopback to forwarded Public IP address from local network - Hairpin NAT

This is a Canonical Question about Hairpin NAT (Loopback NAT). The generic form of this question is: We have a network with clients, a server, and a NAT Router. There is port forwarding on the ...
27
votes
1answer
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What is the difference between a Source NAT, Destination NAT and Masquerading?

What is the difference between a Source NAT, Destination NAT and Masquerading? For example, I thought IP Masqurading was what they used to call it in Linux? But what confuses me is that in our Astaro ...
24
votes
4answers
33k views

Forwarding ports to guests in libvirt / KVM

How can I forward ports on a server running libvirt/KVM to specified ports on VM's, when using NAT? For example, the host has a public IP of 1.2.3.4. I want to forward port 80 to 10.0.0.1 and port 22 ...
23
votes
11answers
38k views

Windows Server 2008: specifying the default IP address when NIC has multiple addresses

I have a Windows Server which has ~10 IP addresses statically bound. The problem is I don't know how to specify the default IP address. Sometimes when I assign a new address to the NIC, the default ...
19
votes
7answers
3k views

Why don't more organizations use inside-to-inside NAT or similar solutions to allow NAT hairpins?

Inside-to-inside NAT aka NAT loopback solves hairpin NAT issues when accessing a web server on the external interface of an ASA or similar device from computers on the internal interface. This ...
17
votes
5answers
2k views

Are people really going to use public IPv6 addresses on their private networks? [duplicate]

I have been reading the Debian System Administrator's Handbook, and I came across this passage in the gateway section: ...Note that NAT is only relevant for IPv4 and its limited address space; ...
15
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3answers
60k views

VMWare networking mode (NAT or Bridged)?

I am running Windows 7 within a virtual Machine from my Mac. I use Windows 7 for Visual Studio primarily and also to host a dev install of IIS. There are two things I need and I am not sure what ...
13
votes
7answers
10k views

Why is it a bad idea to use multiple NAT layers or is it?

The computer network of an organization has a NAT with 192.168/16 IP address range. There is a department with a server that has an IP address 192.168.x.y and this server handles hosts of this ...
13
votes
3answers
16k views

Exposing multiple servers behind NAT using a single public IP address

This is a Canonical Question about NAT and DNS I'm currently trying to set up a network with a DMZ containing a web server and an e-mail server separated from the Internet by a network address ...
12
votes
3answers
18k views

How to configure a custom NAT for use in Amazon VPC

I have an Ubuntu box I wish to use as NAT instance (among other things). I would prefer to avoid using the NAT AMIs provided by Amazon, and instead configuring NAT myself. Currently, my host has a ...
12
votes
4answers
47k views

Differences between bridged and NAT networking

I don't fully understand the differences between NAT and a bridged connection over an virtual machine. As far as I've found, machines which are on the same network with our host machine can access our ...
12
votes
3answers
23k views

Public static ip for vagrant box

I have server (Debian Squeeze) with 1 ethernet card and 2 public static IPs (188.120.245.4 and 188.120.244.5). What I want: Setup virtual box (Ubuntu) with access via static IP (188.120.244.5). ...
11
votes
2answers
24k views

Load balancing & NAT-ing multiple ISP connections on Linux

I have two internet connections from two different ISPs and I need to balance the traffic originating to and from my network between the two ISPs. I am using Debian GNU/Linux. My set-up is like this -...
11
votes
2answers
2k views

IPv6 without nat but what about an isp change?

I haven't worked with IPv6 outside of 4to6 tunneling on my home pc with stuff like GoGoNet. I've read about how it works in a general way. No NAT required (or suggested) and each client uses a public ...
10
votes
4answers
24k views

iptables nat does not exist

Today my iptables nat on the host system stopped working and I have no clue what happend! (That's very bad, I know) All commands are executed as root user. If I run $ iptables -t nat -L I get the ...
10
votes
1answer
27k views

How are cellphone IP addresses assigned?

When my cellphone accesses a website via the tower and its GPRS gateway, NAT ensures that the sites receive a public IP. Would all phones using a single tower have the same IP? If yes, then how can ...
10
votes
2answers
9k views

How to configure a static wildcard subdomain with dnsmasq

I have a network behind a NAT with a few machines. The machines are: router - NAT, dnsmasq, forwarding - directly connected to the inet server - which runs ssh, www and some other stuff clients - ...
9
votes
1answer
8k views

iptables: Port forwarding with masquerading is not working

I'm having some issues with my port forwards. NAT seems to work ok and one out of the port forwards seem to work (udp port 7887 to machine 192.168.1.100). But not the others. I doubt that it matters, ...
8
votes
1answer
869 views

Forwarding traffic from TUN device (C++ backend) to the default gateway

The following problem is just a piece of the bigger solution I have a problem with. All other elements seem working so far, so I'll try to describe very small piece which I have problem with. I've ...
7
votes
3answers
8k views

AWS VPC + IPtables + NAT: Port Forwarding is not working

Yesterday, I posted a question here but I think was not clear enough in my words. BTW, This question is not a duplicate. I have AWS VPC Setup as below. GOAL/PROBLEM: SSH to Server A from internet. ...
7
votes
2answers
6k views

How to persist iptables configuration on Amazon EC2 VPC NAT Ami? [duplicate]

I have a small script like this to configure the iptables: #!/bin/bash PRE_STR="iptables -t nat -A PREROUTING -p tcp -j DNAT" FOR_STR="iptables -A FORWARD -p tcp -j ACCEPT" ########################...
7
votes
5answers
8k views

Accessing the DNAT'ted webserver from inside the LAN

I have a small network with a router, which maintains a connection to Internet, a server and some workstations in a local network. Server is meant to be accessed from the Internet, and there are ...
7
votes
9answers
3k views

Need prosumer router/firewall/vpn/vlan/nat advice [closed]

Looking for a recommendation on a device (or devices I guess) to do router/firewall/vpn/vlan/nat functons for my home network. Right now, I'm doing this with an IPCop box, but I'd prefer a little ...
7
votes
2answers
3k views

DMZ subnet: to NAT or not to NAT?

I'm looking at setting up a DMZ behind a Cisco ASA that will contain a large number of HTTP front-end load balancers and SSL offload services - over 100 IPs, concentrated on a smaller number of hosts. ...
7
votes
3answers
3k views

Amazon EC2 VPC: NAT instance download speed performance drop

I have a set of servers inside Amazon EC2 in VPC. Inside this VPC I have a private subnet and a public subnet. In the public subnet I have set up a NAT machine on a t2.micro instance that basically ...
7
votes
2answers
423 views

FreeBSD's ng_nat stopping pass the packets periodically

I have FreeBSD router: #uname 9.1-STABLE FreeBSD 9.1-STABLE #0: Fri Jan 18 16:20:47 YEKT 2013 It's a powerful computer with a lot of memory #top -S last pid: 45076; load averages: 1.54, 1.46, ...
6
votes
9answers
3k views

How common is NAT within companies (one public ip address)?

How common is for companies to let many users share only one public ip address? I hope the answer is "not very common" since I'm developing software that depends on the ip number being pretty much ...
6
votes
1answer
601 views

How do I configure NAT rules when using ASA IP-SLA when leveraging post-ASA-8.3 NAT syntax?

We are currently running ASA9 at a location with redundant ip connectivity. We'd love to configure ip sla so that internet access survives a single carrier outage. I'm aware of the ip sla commands, ...
6
votes
1answer
3k views

How to traverse carrier-grade NAT (large-scale NAT) to reach VPN Server? [closed]

I currently run an OpenVPN Server via a home network connection that has a single, public, dynamic IPv4 address. My provider (AT&T U-Verse) will apparently soon switch to a large-scale NAT and ...
6
votes
2answers
1k views

Per-user routing doesn't seem to work

So, I'm trying to implement per-user routing so that I'm able to route all btpd torrent traffic over a VPN. Unfortunately, btpd does not currently allow you to bind to a specific IP address. :( I ...
6
votes
1answer
18k views

How do I assign a public IP to a machine behind a pfSense box using 1:1 NAT?

This should be dead simple but for the life of me, I can't get it working. I must be doing something stupid. I have a PFsense server with a public IP address. Behind it is three LAN segments: [ ...
6
votes
2answers
2k views

How do you get AWS VPC EC2 instances to be able to see the AWS APIs?

We're spinning up infrastructure inside of an AWS VPC via CloudFormation. We're using auto-scaling groups to bring up VPC-EC2 instances (so, we don't bring up instances directly; ASGs manage that). ...
6
votes
2answers
17k views

Mikrotik and NAT/Routing issue

I have basic NAT/Routing problem with Mikrotik RB750 that I've been unable to solve over the past days. From our ISP we have 26 IP addresses: 10.10.10.192/27, with 10.10.10.193 being the gateway and ...
6
votes
1answer
25k views

Openvpn routing for lan to lan through tun

I am trying to setup an OpenVPN tun to connect two lan's The open vpn connection is up and working but there is a problem with my routing or nat or something. What I need is an example of what a ...
6
votes
0answers
2k views

IPv6: the end of NAT? [duplicate]

Possible Duplicate: Switch to IPv6 and get rid of NAT? Are you kidding? Is NAT going to disappear with IPv6? What about during the "transition" from IPv4-IPv6? How are we all going to access ...
5
votes
9answers
1k views

Do you think NAT is largely responsible for the delay in IPv6 adoption?

I'm wondering if this is really the case, or, if when IPv6 does get widespread adoption, we will still hide all the machines on a network behind a single (or few) IP address under the assumption that ...
5
votes
2answers
12k views

Windows 7 with internal port redirection, is it possible?

I received a request from one of our developers that I am having trouble solving. Here in the office they use linux desktops and I can forward the localhost:80 via a iptables nat to localhost:8080. ...
5
votes
5answers
847 views

NAT as a firewall

Network Address Translation ( NAT ), seems to sort of act as a firewall for the hosts behind it because they are not available. Although I would never rely on this as my firewall, what are its ...
5
votes
3answers
5k views

Unable to connect on natted server from a host computer on the same LAN using public IP address

I have a server statically NAT’d using a registered IP address and it is accessible from the outside. The problem is I cannot access my server from the inside using the registered IP address with a ...
5
votes
2answers
2k views

Symmetric NAT and UDP Hole Punching

I've read this question, but the explanation of Symmetric NAT wasn't detailed enough. Please could someone help me to understand the following paragraphs? I read this about Symmetric NAT: Each ...
5
votes
1answer
21k views

Ping: sendmsg: operation not permitted error after installing iptables on Arch GNU/Linux

Yesterday I got a new computer as my homeserver, a HP Proliant Microserver. Installed Arch Linux on it, with kernel version 3.2.12. After installing iptables (1.4.12.2 - the current version AFAIK) ...
5
votes
3answers
7k views

How to get VirtualBox NAT working with actual client IP's?

I'm using Virtualbox 4.0.10 on a Debian Squeeze box. I have a Windows 7 VM that I use to host a game server. After setting up NAT and port redirection, clients can connect to the VM, but the game ...
5
votes
7answers
26k views

Yum update not working on CentOS 6.2 minimal install

Note: This is my first question on the stack exchange network so please give mercy and provide guidance where needed. I have installed a CentOS 6.2 KVM guest and I am having problem getting yum to ...
5
votes
3answers
802 views

What's the best way to accomodate multiple devices that all want to use the same fixed IP address into the same LAN?

Suppose I have an ethernet capable device that has a hard coded IP address in it. I have software that works with the device, which could be configured to work with practically any IP address for the ...
5
votes
3answers
686 views

IPv6 and NAT, routing to multiple ISPs

Currently I have a nice setup using private IPv4 address space and uplinks from two ISPs to the Internet. Thanks to NAT I can just take down one of the interfaces and the Internet access is still ...
5
votes
1answer
136 views

Running multiple services on different servers with IPv6 and a FQDN

One of the things NAT has permitted us to do in the past decade is split physical services onto different servers whilst hiding behind a single interface. For example, I have example.com behind a NAT ...
5
votes
2answers
3k views

Secure NAT setup with iptables

I have a Debian running device that needs to act as an internet-gateway. On top of that I want to provide a firewall that not only blocks inbound traffic, but also outbound traffic. And I figured ...
5
votes
1answer
4k views

Need to duplicate UDP packets to multiple destinations via iptables

I'm looking to duplicate UDP traffic for SYSLOG and NetFlow data and was hoping to use iptables to do so, but so far I'm not having much luck. I'm aware of other user space software packages that can ...