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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Server becomes unreachable and comes back up on its own (most likely a network issue)

I'm having a strange problem with a server I have sitting at my workplace (it's behind a NAT, if that's important). The issue is that at some times, it becomes unreachable and then comes back up ...
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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. ...
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2answers
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Iptables string

I have an iptables rule like this: iptables -t nat -I PREROUTING -p tcp --dport 80 -s 192.168.1.2 -j DNAT --to-destination 192.168.1.1:80 it works perfectly.. but I want to redirect only for one ...
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1answer
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How can I Nat certain boxes in my datacenter so that they are coming from a single IP

I want to NAT a certain group of servers in my datacenter so that they all access clients from a single IP. This will make it much easier for documentation that we provide clients. However there ...
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Domain Controllers over a NAT

My organization is in the process of setting up a new network at a hosting provider for a very large application project. Since the whole system uses Active Directory we are planning on using a pair ...
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3answers
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Can I have web server on a home network with 1 public IP address? [closed]

I've got a fairly standard home network with a modem from my ISP, which is connected to a router which then provides NAT to about 3 PCs and laptops. There's a possibility to obtain one public IP from ...
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Is NAT completely transparent to a host?

Can we find a sequence of packets that a host can transmit to determine whether it is located behind a NAT box? I mean, without any special server support like STUN.
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How to implement Nat loopback/reflection?

I'm trying to access a server on my LAN via its public IP address. External clients can connect just fine, but I'm unable to do so from within the LAN. There is a separate rule in the NAT settings of ...
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1answer
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Cisco ASA 8.4 port forwarding

I am having trouble port-forwarding on an Cisco ASA from a host on the internet to a host on the internal network. The outside interface of the ASA is assigned via DHCP. Is there something else that ...
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2answers
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UDP and NATs - is the timeout bidirectional?

Is the timeout for an UDP connection through a NAT reset every time a packet is sent OR received by the client, or are there any (common) implementations that require the client to actively send ...
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Make CentOS 7.x a port forwarding NAT device

I would like to make CentOS a port forwarding NAT machine using iptables. This is the first time I've tried this and I think i might need a little help. This is the configuration i'm trying to ...
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IPtables NAT puzzler: Why is traffic from the firewall host being NATed even though it's not coming from one of the prescribed source addresses?

I run a small network where a linux web/mail server also provides NAT for a collection of windows boxes. One of these windows machines is apparently misbehaving (ZeroAccess botnet even though I can't ...
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292 views

Networking several devices with the same IP

I have a bunch of embedded devices that I need to flash with a custom OS. On each device, the boot-loader (U-Boot) has a fixed IP of 192.168.100.2 and on boot it looks for a TFTP server at ...
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2answers
810 views

Public IP behind NAT firewall

I have a Linux NAT Firewall serving a virtual machine infrastructure. Right now all the VMs use NAT, but I'd like to have some of them to use a public IP that is not NATed. I have a range of IPs: ...
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2answers
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How can I setup a Firewall without NAT?

We have 16 IP addresses from our ISP, and are setting up a SonicWall Firewall. I'd like to have the SonicWall do NAT for the LAN, but act as a firewall only (no NAT) for the servers which are using ...
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4answers
889 views

Networks, subnets, routing and NAT

What I'm going to ask may be trivial but I really need to understand cause my teacher is confusing me! That's the problem. I got 2 private networks The first is a class C network and the address is ...
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3answers
576 views

Port Forwarding

Assuming port forwarding is done on router, can the router forward if the data is coming from local machine, rather than remote. For example: Sender targets ip like:88.251.xxx.xxx, port 8999. ...
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Routing application traffic through specific interface

First question here, so please go easy: I have a debian linux 5.0 server with two public interfaces. I would like to route outbound traffic from one instance of an application via one interface and ...
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Marking packets with iptables with a NAT

I have to write bash scripts for a router to control bandwidth limitation for a given user on a given domain name. For this, I'm using iptables to mark the packets incoming from a restricted domain ...
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2answers
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Linux Routing with two NICs (LAN vs Internet) with NAT and bridging for VMs

My Setup: There is only one physical machine in this setup, a Host System for Virtual Machines (VMs) with two network adapters. One NIC (eth0) is connected to an internal network (LAN subnet, e.g. ...
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1answer
256 views

What is the correct iptables rule when NATing multiple private subnets?

I have a Centos minimal 6.5 acting as a router. eth0 is connected to a Cisco switch trunk port, allowing VLANs 200-213. I have several VLAN interfaces just as this link suggests: ...
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1answer
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How to Configure Source NAT (Private IP => Public IP Outbound)

I'm running VMWare ESXi Free and have Zentyal SBS 3.2 running as a Gateway. I have 5 Public IPS (CIDR/29, let's call them 69.1.1.1 - 69.1.1.5) and currently Zentyal is bound to 69.1.1.1 as the ...
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How are connections differentiated from behind NAT routers?

Background: I have a very simple server program written in PHP. It's mostly working, but only as long as there is not more than one client per site. Questions: How does a NAT Router (typical SOHO ...
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How to redirect ports for on a virtual interface?

There are two IPs associated with one physical network interface eth0 and eth0:0. The following works fine for the first interface: iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 80 -j ...
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iptables asynchronous NAT. packets drop after prerouting table

I have a Centos server acting as a NAT in my network. This server has one external (later ext1) interface and three internal (later int1, int2 and int3). Egress traffic comes from users via int1 and ...
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Routing requests from external hostnames to internal IP addresses in Ubuntu

I want to host several websites using the same IP address. My ISP gives me one static IP address, however I have three different webservers (all running different sites) hooked up behind a cheap ...
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1answer
619 views

IP NAT pool range

When is it necessary to setup a pool of more than one address? So if I have this ip pool range: ip nat pool demo 72.32.11.65 72.32.11.66 netmask 255.255.255.252 What's the difference if I just have ...
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How do I setup Windows Server 2008 as NAT with one NIC?

How would I setup Windows Server 2008 as NAT router with only one nic? I only have access to a server with one nic and I can't add a nic to the server.
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3answers
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Cisco ASA NAT - internal host see its public ip

I have a server hosted by a provider which uses Cisco ASA to do nat. The problem I have is that the internal server that is nat-ed with a public ip will see its public ip as source ip. This basically ...
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1answer
729 views

How can I know if NAT instance is becoming a bottleneck

I'm running my own NAT instance inside of an AWS VPC. I want to make sure that the NAT instance will not be a bottleneck and to that end would like to set my own expectation for when to scale to a ...
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Linux - two subnets, one interface, one gateway - NAT the additional subnet

We currently have a few servers that all use the same LAN: Host1: eth0 10.0.0.1/24 Host2: eth0 10.0.0.2/24 Host3: eth0 10.0.0.3/24 Gateway: 10.0.0.254 We want to run some VMs (VirtualBox) on these ...
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iptables: combine SNAT with network remapping for OpenVPN

[Apologies for the long prelude; question halfway down.] I have a working OpenVPN setup whereby a VPN server pushes a route back to one client (hereafter called the “router”) which can then expose ...
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944 views

Sharing an internet connection from a virtual Windows 2012 AD Server

I have a virtual HyperV network used by a number of virtual development and testing servers and an all-in-one Domain, DNS, DHCP server; I want to keep the many virtual servers separated from our main ...
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Cisco Network Object NAT to get Internet?

So I've inherited a Cisco ASA 5505, and I have no experience whatsoever with the things! There are two Network Interfaces both WAN facing, and the LAN interface of course. Now in NAT rules, there are ...
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How can I NAT traffic for one VPN to come from a different IP on Cisco ASA?

I have a Cisco ASA firewall between our private network (10.1.0.0/16) and the outside world, and multiple VPNS going to client sites. Existing: [10.1.0.2...] = source client | [10.1.0.1 ASA ...
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tcpdump not picking up traffic redirected by iptables

The following iptables rule is used to redirect all internet traffic coming in from eth1 to port 3000 at localhost (interface lo with ip 127.0.0.1): iptables -t nat -A PREROUTING -i eth1 -p tcp ...
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706 views

Building a router / NAT and need to compare performance of FreeBSD 8 v RHEL 6 [closed]

I am going to be setting up a router and NAT device but I am unable to choose between pfSense 2.x (FreeBSD 8) and RHEL 6. The device will need to forward a medium (2k hosts) sized network where ...
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1answer
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OS X 10.8: redirecting locally initiated ssh connections to localhost:22

I need to hack the OS X pf to redirect all ssh connections from an user to this machine. I want, when doing $ ssh google.com to get the same results as with $ ssh localhost ie a connection to ...
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1answer
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ASA Static NAT Understanding

I have an ASA configured as follows; Inside: 192.168.0.254/24 Outside: 10.0.0.1/29 (This is routed to the ASA) global (outside) 1 interface global (outside) 2 10.0.0.2 nat (inside) 1 0.0.0.0 0.0.0.0 ...
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many different TCP timestamps through NAT device cause server to drop packets (PAWS)

Various workstations behind the client side Network Address Translation (NAT) firewall are sending timestamp information on the TCP packet to our server. The packets from many workstations arrive ...
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1answer
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Cisco ASA Nat 8.4

I'm trying to get port forwarding on my ASA working. I'm using: object network server1 nat (inside,outside) static interface service tcp 25 25 and an access list, and it works fine, however, I ...
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1answer
171 views

iptables masquerading and rejecting outside-to-inside

I found masquerading made simple howto very useful and everything works just fine. But I'm not sure about the last line: iptables -F iptables -t nat -F iptables -t mangle -F iptables -t nat -A ...
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2answers
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Making Ubuntu a minimal NAT?

I need to make a quick-and-dirty NAT out of a Ubuntu 10.10 box. Just "this side is NATted with DHCP handing out 192.168.x.0/24" and "this side gateways to the Internet", and nothing else interesting. ...
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How can I copy from a server on the internet to a server behind a router doing NAT?

I have both a VPS and a server behind a NAT firewall. I want to use the server behind a NAT firewall as a backup for the VPS. The VPS needs to be able to initiate the backup process and send the ...
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Best way to monitor network traffic through a linux gateway

I have a linux box set up running as a router using iptables. My question is: What is the best way to monitor the traffic passing through it, on a per-IP basis? I've tried using Ntop, but it just ...
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OpenWRT Barrier Breaker - Router does not route

I've upgraded my TP-Link 1043 router to OpenWrt 14.07. Everything is perfect, Wifi and LAN are bridged, LAN machines can access each other by name, I can SSH into the router, and the router can access ...
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528 views

Setting up NAT for multiple isolated networks with iptables

I have a gateway machine connected to multiple internal networks that I would like to set up NAT on. The catch, though, is that these networks need to be isolated from each other, which I haven't been ...
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1answer
655 views

Can't connect to instance via floating IPs, not natting/forwarding properly

I'm having trouble getting floating IPs to work properly on my OpenStack setup. It looks like the controller node (running nova-network) isn't forwarding the traffic to the instances. I've got a ...
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3answers
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Is it possible to capture packets of a Router?

I am facing an issue that some packets sent out to internet from inside network were missing. The pattern we are using is like: Client A ←→ Switch A ← Router A:NAT ← .. Network .. → Router ...
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Netgear VPN LAN2LAN address translation

Here's my question: I have set up a VPN IPsec LAN2LAN (or site2site) with the following parameters: local subnet: 10.178.51.64/27 remote subnet : 10.174.0.0/16 The vpn tunnel comes up correctly ...