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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(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 ...
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630 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 ...
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272 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 ...
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73 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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248 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 --add-forward-port=port=2023:proto=tcp:...
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141 views

Redirect traffic destined for IP and port

I have a program that wants to connect to 1.2.3.4 on port 5678, but it can't because the port is blocked on our network. However, I do have an SSH tunnel set up that redirects localhost:5678 to 1.2.3....
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217 views

Observing ping replies under DNAT

I'm confused while trying to understand the DNAT mechanism under below circumstance. My understanding: DNAT = Destination Network Address Translation: Functionality which translates the destination ...
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269 views

Routing packets between networks with iptables

I'm trying to create a proxy of sorts using just iptables. The linux computer (my proxy) has two ports: p2p1 is connected to the Internet. em1 is connected to a local network. There are two ...
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358 views

Why aren't my iptables rules appearing in the relevant list after reboot?

I am trying to write two persistent NAT rules, which I save via iptables-save > /etc/iptables.ipv4.nat, and restore upon reboot via pre-up iptables-restore < /etc/iptables.ipv4.nat in my /etc/...
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267 views

Managing iptables for home lan routing

I have a LAN at home. One Netgear router - 192.168.0.1 connected to the internet. One Macbook - 192.168.0.10 (connected to Netgear router) One PC with Kali Linux - 192.168.0.20 (connected to ...
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Does “ip_forward” need to be enabled for any iptables SNAT/DNAT (postrouting/prerouting) rules?

I remember I had to enable ip_forward kernel parameter in the past in order to run SNAT/DNAT rules in iptables successfully. Today I was reading this post: http://blogs.aws.amazon.com/security/post/...
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178 views

KVM - nat or bridge. How I do that

I have Debian Jessie server, and I have install apache server. From apache hosted several sites from different ip address. My server have resources for KVM. My question is - How I can set my free IP ...
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248 views

Host a server with NGINX using VPN behind a NAT

so I was hosting a server using NGINX on a Raspberry Pi using a T-Mobile mobile router. All was working fine, till I noticed today that T-Mobile started to put me behind a NAT sometimes. So I heard ...
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67 views

Nat with saving real client IP

I have this schema: Client -> NAT server -> Game server On NAT server I have the following rules: iptables -A FORWARD -d $MC_IP -p tcp --dport 25550:25580 -j ACCEPT iptables -t nat -A PREROUTING -d $...
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155 views

SSH E-mail login alert if SSH port is as NAT

Can you help me with this problem please? How can I set e-mail alerting after SSH login when port 22 is NATed? I use Linux Debian 7. I have used these iptables rules: eth0 - external network, eth1 - ...
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937 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 ...
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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 ...
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116 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 ...
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397 views

SNAT with firewall-cmd?

I have an interface with multiple IP Addresses (on CentOS 7), which is in zone "external" (with masquerade on). I want to specify that, if a connectiona attempt to a specific address goes out, to use ...
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50 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 ...
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196 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, ...
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63 views

How to do iptables nat loopback?

I have a linux server behind the ISP's cablemodem-router combo. With some hacking I was able to make the port forwarding work, and the DHCP exceptions in the udhcpd. But I wasn't able to do the NAT ...
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43 views

scp to a KVM guest behind NAT

I have a KVM guest running on a server accessing it via virt-manager. I'm running the guest from my_pc. server has a public IP address and both my_pc and guest can ssh it. guest has a 168.192.x.x IP ...
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29 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 ...
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30 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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148 views

Can not reach local DNS server for local dot domain subzones because firewall returns gateway IP

I have pfSense inline between my cable modem and my switch, on pfSense I have a NAT port forward on 53 to my local DNS server which I want to serve local subzones to the LAN with. Right now when I dig ...
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51 views

Shorewall configuration : providers and LAN

Hi all and thanks in advance for the answers. Currently, I have different providers configured in shorewall. I'll will probably have to change one of them. The problem is I won't have any Public IP ...
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Outgoing masquerade address changes after adding a second interface to the bridge

In fact I have the following configuration: extrouter(192.168.1.1) <- wifi -> [eth2 (192.168.1.11) Centos 6/6 based host br0 (172.22.5.254)] br0 contains two tap interfaces (tap0/172.22.5.1 tap1/...
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193 views

Use VirtualBox to access site on host from guest? the host and guest is linux

I'm running VirtualBox on a Ubuntu (host), the VM I’m using is fedora (guest). VirtualBox is setup to use the NAT network adapter, and I'm able to get to the internet. I use Port Forwarding to access ...
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312 views

Connect to IPsec VPN using OpenSwan

I'm connected to Internet with a simple ADSL router with NAT. I have a smartphone and a laptop running linux. I need to connect to a IPsec server using OpenSwan. First I tested that it is possible to ...
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NAT-T set up using 3 linux machines

I am trying to have a simple NAT-T setup using 3 linux machines. Linux1 Linux2(NATdevice) Linux3 (eth0) 192.168.1.51 <--->(eth1)192.168.1.80 & (...
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iptables server behind NAT accessible from outside as well as inside the nat

I have 2 machines with a KVM running on each machine - so two kvms with the below networking Host 1: 192.168.10.100 (eth2) 10.10.100.1 (virbr1) KVM 1 (NAT with Host 1): 10.10.100.128 (eth0 ...
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SNAT / Masquerade with shorewall

I've got a little question about Masquerading and SNAT in combination with shorwall and KVM. The Operating System is Scientific Linux 6.4. Setup is like this at my root server: Virtual Machine IP ...
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Connect to libreswan with ikev2 and behind nat

Server (Scientific Linux 7.2, like CentOS 7.2) with libreswan 3.15.7 in the internet cannot respond to a connection attempt if the client is behind NAT and insisting on using ikev2. It basically ...
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Networking, tl-wa5210g boadcast, dhcp. droping packets

Hi i have strange problem IPS is polish UPC and coaxial router This is technicolor with dhcp enabled Addres is 192.168.0.1 As my main gateway It is connected to the router as Ap in wpa2 wich one ...
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16 views

ALG IPSEC and RSTP

I have linux 3.18. my Linux is installet on a router. in this router I activate a NAT from the wan side. Does this Linux support ALG of IPSEC and RSTP ?
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iptables Dynamic SNAT, how to force to use different src ip from pool?

Requirement: I need to translate a private-ip range to a public-ip range while going out on the internet. It should be a one-one mapping, if public-ip range exhausts it should drop to the next nat ...
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202 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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33 views

How do I change NAT type for UDP to be more P2P-friendly?

On gateway I do iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE, and on device I have this: $ stun stun.counterpath.net STUN client version 0.96 Primary: Indepndent Mapping, Port Dependent ...
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70 views

linux to linux IP MASQUERADING failed (can't ping ip server)

I'm new in linux, i'm trying to IP MASQ. So the diagram is like linux A is connected to HUB and Internet, and linux B is connected only to HUB. In linux A i have eth1 (10.10.10.5) and eth0 (192.168.1....
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747 views

strongSwan routing issue with roadwarrior behind NAT

Using the following ipsec.conf configuration: conn %default ikelifetime=60m keylife=20m keyingtries=3 rekeymargin=3m keyexchange=ikev2 esp=aes-aes256-...
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203 views

SSH Public key fails when using Reverse SSH Shell

I have a machine behind a NAT, which I would like to access via ssh. Lets call this machine A. I have machine B, which is publicly reachable, which I would like to route my ssh connections. I have ...
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586 views

CentOS as home network router: IPTables Port Forwarding failure

I have currently set up a home server with a CentOS 6.6 installation on it. The server has two NIC interfaces which I'm using it as my router and DHCP server. Here's a diagram showing the network ...
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530 views

Slackware internet gateway with iptables / poor browsing performance

I am running a dual core headless computer as internet gateway via pppoe with two NICs. eth1 (internet interface) no ip, no dhcp eth0 (LAN interface) - 192.168.0.100 static ppp0 - dynamic ip ...