Questions tagged [nat]

For questions about Network Address Translation (NAT), a method of modifying network address information in IPv4 packet headers.

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Are there STUN implementations that can sometimes handle symmetric NATs? [closed]

I've been working on connecting two devices that are each behind a symmetric NAT and managed to make it work quite consistently. However, it takes quite some time for the connection to happen (...
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102 views

Can a server on the other end of a site-to-site vpn be exposed (NATd) to a public IP on an ASA

AWS DataCenter ----------- site-to-site VPN ------------ http server <=======================> Cisco ASA public address 10.0.1.59:443 ...
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IP masquerading and nat

what is the difference between IP masquerading and nat? do both of them have the same limitation? in the line "IP masquerading cannot provide full internet connections to the hosts which hide ...
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Configure nat on src ip to dst port

I wondering about some workaround for issue that I have: I have 2 sources which generates multicast to 224.1.1.1 and port 12345. I'd like to configure on my Cisco IE 3000 NAT which will change the ...
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How does 2 computers both behind NAT routers handle communication? [duplicate]

Currently reading up on TCP/IP protocol stack, while I was reading about the Network Interface layers, I started reading about NAT, and how it meant to decrease the amount of IPv4 used, by using the ...
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66 views

Cisco IPsec VPN tunnel problem

I have a problem with VPN configuration. This is the topology I created: First updated licenses to make the VPN available: license boot module c1900 technology-package securityk9 IPsec Router ...
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1answer
199 views

Cisco, Router can communicate; hosts cannot

I am learning CCNA related tasks, I have picked up a Cisco 1900 Series router. I am attempting to set it up behind my existing router (Comcast standard router). My "Real" network is 10.0.0.0/...
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48 views

NAT cannot communicate with 2 network

I have configured BGP for routing and NAT for HQ and Branch. I can ping from windows / server to public IP and also Linux Mint ping to public IP. but, I cannot ping / communicate between network HQ to ...
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45 views

Need a little clarification with NAT and IPv6

I understand NAT exists to not exhaust all the ipv4 addresses so there is no need for it with ipv6. So with ipv6 having an unimaginable amount of addresses, will every device have its own public ...
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Trace internal equipement from Internet while answering

I would like to know if it's possible to achieve a traceroute of nodes on an internal network from an equipement on the internet answering to a query. Let's say that a client on an internal network ...
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2answers
60 views

Is NAT66 a Viable Option to Protect Client?

Due to the addressing scheme of IPv6, each client now is able to get and directly use Globally-Routable Address (GUA) from the ISP. But that poses bigger security threat because attacker can directly ...
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Combining NAT an tunneling

I was reading a text and a doubt came to mind. Suppose there is an interface in a router that implements NAT. That same interface is the extreme of a tunnel. If I was to send a message through said ...
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38 views

How to Mitigate DoS by Bindings/Transport Address Exhaustion in NAT64?

Let's say a NAT64 Router only has 1 IPv4 address for bindings, meaning the NAT64 router has a roughly 65535 IPv4 transport addresses. A malicious attacker can then exhaust the entire IPv4 transport ...
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Why does IPSec's Transport Mode ESP can't be used in NAT64 although ESP doesn't sign the new IP header?

In RFC6146 stated: Any protocols that protect IP header are incompatible with NAT64. This implies that end-to-end IPsec verification will fail when the Authentication Header (AH) is used (both ...
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Why does CLAT in 464XLAT architecture use Stateless NAT64 instead of Stateful?

As of my understanding, stateless NAT is using 1:1 translation, meaning it needs one IPv4 address for one IPv6 address vice versa, thus not preserving IPv4. Since the CLAT is supposed to be router/...
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General: What is a dynamic gateway, how does it work, where is it used?

I saw this option in my OPNsense gateway configuration, and was hoping someone could shed light on what it is, exactly: Dynamic gateway policy: [YES/NO] This interface does not require an ...
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1answer
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Is an IPSec connection between 2 devices behind NAT possible?

We have tens of IPSec connections between our office and customer site's. We use an extra router in the customer network (so behind NAT) to initiate the connection to our office where a PFSense router ...
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37 views

How to connect to a machine which is sitting behind NAT router?

I have a server that needs to push a message to a client from which it received a request a few days ago. Now request which was received has the IP address of the NAT router behind which the client ...
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2answers
58 views

Cisco Port forward ip nat inside source static … Invalid

This is almost the same question as How to setup port forwarding on Cisco Router running Version 15.2(4)M6. The problem is that the command used in the answer is not available: ip nat inside source ...
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53 views

Why does my enterprise issue me a public IP address instead of just a private IP address?

Let's say I work for a big enterprise organization. When looking at my IP address, I notice that it is not a private IP address but is instead a public IP address. What are the benefits of ...
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56 views

NATTing a server address

I need help writing NAT rule for this use case: I want to be able to connect to an local IP as though it's the remote server IP. e.g. port forwarding. I don't have access to the firewall on the remote ...
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102 views

Cisco NAT - Overload PAT and Static nat from one inside to two outside interfaces

i have following setup Cisco ISR4k Router with one inside LAN interface and two outside Interfaces. ---- WAN1 (NAT outside) LAN (NAT inside) -- ISR4k | ...
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port address translation

I was reading about different type of NETWORK ADDRESS TRANSLATION (NAT) techniques from a book, and was reading about a special type of NAT that is called port address translation, and it's known that ...
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Cisco: NAT overload does not work on Serial point to point interface /32 address on Cellular modem

I have a LTE modem installed in a Cisco 1921 that is able to connect to the carrier network and ping out sucessfully from the router, however NAT hosts are not able to connect to the internet. There ...
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1answer
495 views

Destination NAT on Cisco ISR

I know how to perform regular overload PAT in my lab running sh ver Cisco IOS XE Software, Version 16.03.09 Cisco IOS Software [Denali], ISR Software (X86_64_LINUX_IOSD-UNIVERSALK9-M), Version 16.3.9, ...
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IPSEC between two offices with SAME local networks. How should I do nat? [duplicate]

I have two spokes with same local networks and want to do IPSEC between them. When I try to ping 172.17.214.111 from 192.168.5.0 (from right side to left side) I see packet on Cisco router and I see ...
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162 views

PAT with multiple VLAN

I've set up a network with 4 VLAN, 3 VLAN configured PAT on it and 1 VLAN configured STATIC NAT. The router is acting as the DHCP server. Outside of my router I have another router acting as "the ...
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Two PC on the same LAN, communicating the same Server

Assume that we have 2 pc on the same LAN, local IP of pc1: 192.168.1.5 local IP of pc2: 192.168.1.6 Now suppose that both pc1 and pc2 wants to connect to a server on the internet, we all know that the ...
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DMZ host is not reachable from LAN [duplicate]

I have a pfSense firewall with WAN, LAN and DMZ interfaces. A server is residing in DMZ with private ip 10.0.0.2. Therese a 1:1 NAT in WAN interface that is mapping a public ip X.Y.Z.213 to 10.0.0.2, ...
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Public IP address does not work in internal network [closed]

I have configured port forwarding to my system from the router configuration menu, when I try to access the public IP address in the internal network it does not respond but it is accessible outside ...
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2answers
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Possible typo in Tanenbaum's book about NAPT

From what I have understood from multiple sources (web and other books) about the concept of NAPT (also called NAT overload or IP masquerading in Linux environment), if there is a scenario like the ...
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84 views

Static NAT and PAT

I have two private IP addresses, want to make them NAT to 203.0.113.0/2 public IP address. WAY 1 : Static NAT (2 ip addresses NATted to one by manually) WAY 2 : PAT (Router gives port number ...
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CMTS (DOCSIS 3.0) with CGN (CGNat)

For a new project/building I am working with the CMTS model MA5633-XB10 by Huawei. The usual way is done by implementing two DHCP servers in the same VLAN, from which the CPE gets the private IP ...
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2answers
495 views

What happens when a NAT router reaches its 65,535 connection limit to a specific destination?

If a company of thousands of end points all try to access a specific destination (let's say google.com), then the maximum TCP connections it can have in total is limited to 65535 connections, based on ...
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1answer
789 views

pfSense 1:1 NAT Not Working

Next year, if I have the money for it, I want to get a dedicated server (either from Hetzner or OVH) and some IPs (maybe like 16 IPs). The server will have Proxmox and VMs will get their network ...
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3k views

Why is symmetric NAT called “symmetric”?

After searching a while, I'm still not able to find a logical explanation on why is it called symmetric NAT. Where lies the link between symmetric NAT and that each request is mapped to a unique ...
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157 views

Cisco router on a stick with public ip wan (ISP)gateway

I am trying to create a router on a stick with an outside facing sub-interface with a public IP from an ISP. I have tried to configure NAT and routing but I just cant get to ping the internet. I'm ...
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1answer
116 views

Issue w/ Cisco router and failed NAT and static default route

I have a cisco router that is using a VRF to support a site to site VPN tunnel. I have added a second network to the router for non-VPN standard internet use. My problem is that my default static ...
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2answers
101 views

How Does Network Address Translation Work Initially at the End Point Router

I have come across a question that I can not seem to get a quality answer to. I understand how NAT works when a reply packet is received and how it is mapped back to an internal IP address from the ...
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135 views

Static port forward 1194 to VPN server behind Cisco router

I'm trying to setup a VPN server behind a Cisco router which is my main internet gateway. I've set it up as shown in the attached picture. The problem I'm observing is that zero packets with a ...
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2answers
45 views

Why doesn't NAT drop packets with spoofed public source IP?

As I read on Section 4.3.8 of this page https://www.manrs.org/isps/guide/antispoofing/, The following code: ip nat inside source list INSIDE pool OUTSIDE overload will translate packets with a ...
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1answer
51 views

Cisco ASA NAT/PAT Multiple WAN IPs

I'm trying to setup a NAT / PAT in ASA 5520, I'm able to do so very well when the Public IP I want translated to Internal host is configured on the Outside. Question is the ISP provided 1.1.1.1/30 ...
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42 views

Why does Network address translation (NAT) need Port Address Translation (PAT) if IPs are different in the internal network?

For example, there are several servers in the local network 192.168.0.1, 192.168.0.2, 192.168.0.3, etc. They are connected to one public IP. Why does NAT also assign ports to each local IPs that are ...
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92 views

Do NAT devices need to have private IP addresses?

If a NAT's job is to create mappings between internal ip/port pairs and external ip/port pairs with one Internet-routable IP address, does a NAT need a private IP address for itself? I think one ...
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282 views

Debug ip nat in IOS XE

I used to use debug ip nat in IOS to show NAT translations happening. On a Cisco C1111-8P running IOS XE, this command does not exist anymore: router#debug ip nat % Incomplete command. router#debug ...
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What's the difference between “IP NAT Inside Source” and “IP NAT Inside Destination” commands in Cisco routers? [duplicate]

As much as i know both of this commands translate source address of packets that travel from inside to outside and destination address of packets that travel from outside to inside,so what's the ...
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115 views

Cisco ASA static nat one-to-many from interface address to object-group

Syntactically, the following set of statements is valid (at least as of 8.3): interface Ethernet0/0 nameif OUTSIDE ip address 192.0.2.1 255.255.255.0 interface Ethernet0/1 nameif INSIDE ip ...
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1answer
101 views

Prevent static NAT to respond to ARP requests

We are trying to merge 2 networks with overlapping IP spaces: This is the configuraiton so far: interface Tunnel1 description VPN Port CompanyA ip vrf forwarding LAN ip address 172.18.0.79 255.255....
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Segregated network - managed switch or router?

I have 3 pc connected to a switch that is connected to a bigger network. I want those pc to live in their network and don't expose their ips. (in this very moment the scope is accomplished using a pc ...
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71 views

When a packet is received, how does it know which internal machine to send it to?

I am familiar with ARP and routing, but I think I am failing to put two and two together here. On an IPv4 packet we have the source IP address, which allows any router to send the response back to the ...

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