How do router select ports for port NAT?

Suppose my computer (LAN address accesses via its local port 56789 to via port 1234. If I understand correctly, the following things happen:

  1. My computer sends a packet with a header src:, srcport: 56789; dst:, dstport: 1234
  2. My router translates the packet's header to say src:, srcport: X; dst:, dstport: 1234, where is my router's public IP address (the one I get when I ask Google what is my IP)?
  3. My router remembers this translation and all connections in the other direction are translated src:, srcport: 1234; dst:, dstport: X to src:, srcport: 1234; dst:, dstport: 56789

My question is: what is this? X that the router dials? Is it predictable? Does the brand and model of the router matter?

VMWare – Nat / Bridged or Host only?

I don't understand that much about networks, so I should ask. I am using VMWare so that I can use a Linux guest on my Windows host. I wanted a "secure environment" for home banking and so on … Which network configuration would be more secure? I don't want the guest to interact with the host or the host to interact with the guest.

Thank you so much!

IPv4 over NAT and IPv6 directly to VM

I cannot get IPv6 Route + IPv4 NAT to work on my Proxmox host.
(I have an IPv6 subnet and a single IPv4)

With this configuration, the VM is also not accessible via IPv4 port forwarding.

The IPv6 assigned in the VM can never be accessed. Neither from internal to external nor from external to internal.
Without IPv6, the VM can be reached from outside via IPv4 NAT.

It would be super nice if someone could write me detailed instructions on how to set up the IPv6 route and IPv4 NAT;)

Here is my modified one /etc/network/interfaces

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

# IPv4 Host
auto ens33
iface ens33 inet static
        up route add -net netmask gw dev ens33

# IPv6 Host
iface ens33 inet6 static
        address fe80::ffff:ffff:ffff:4441/64
        gateway fe80::1

# VM Bridge IPv4 NAT
auto vmbr1
iface vmbr1 inet static
        bridge-ports none
        bridge-stp off
        bridge-fd 0
        post-up echo 1 > /proc/sys/net/ipv4/ip_forward
        post-up iptables -t nat -A POSTROUTING -s '' -o ens33 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s '' -o ens33 -j MASQUERADE

# VM Bridge IPv6 Subnet route
##iface vmbr1 inet6 static
##       address fe80::ffff:ffff:ffff:5/64

# ---------------------------------

# IPv6 proxy

# IPv6 VM1
ip neigh add proxy fe80::ffff:ffff:ffff:10 dev ens33

# ---------------------------------

# VM IPv4 Port forwarding

# VM1
post-up iptables -t nat -A PREROUTING -i vmbr1 -p tcp --dport 80 -j DNAT --to
post-down iptables -t nat -D PREROUTING -i vmbr1 -p tcp --dport 80 -j DNAT --to

ens33 = host ethernet

vmbr1 = VM bridge

Network – How can I assign a static IP to a VMWare guest with NAT Network Adapter?

I am creating VM Workstation Linux guests with NAT network adapters and I want some of the images to have static IP addresses.

I have read this suggested solution, but cannot get it to work. It seems to ignore my entries and rewrites the configuration file frequently. It also seems to be a cumbersome solution to maintain more than a few pictures.

NB: I am using VMWare Workstation v10 and v12.

nat – Attempt to run a local server with port forwarding behind a carrier-grade network from the ISP, but no connection to localhost is established

I am trying to create a half life server by port forwarding through my router. It didn't work, I checked it out, and my public IP and my WAN IP were different. Then I realized I was in a carrier-grade network. I called the ISP and asked them if there was a way to do this without having to route to my router, and they said the guy is doing my router as a DMZ host. That was what I needed, requests to my public IP on any port were forwarded and forwarded to my router, and then my router only forwarded the port I was interested in, port 27015, UDP port of the half- Life server standards.

But it didn't work, I made sure that my localhost had a static IP and configured the DHCP to reserve one for me, created firewall rules to allow traffic on the 27015 port, and that I had all the correct ones I used IP addresses for my localhost, my default gateway, my pale address and my public address.

Me and the ISP guy chatted again and we decided the port was somehow closed. I quickly set up a Filezilla server (I forwarded 27015 as a listening port and a range of 11000-12000 to transfer files, both in the router and firewall rule) and asked if he wanted my home- List of my public IP and my port 27015. It worked, so everything was fine, checked with Wireshark.

Now I'm in a situation where I want this to work, but I'm not sure what's going on. The ISP type doesn't help much, and I think either the DMZ it set up doesn't allow UDP packets because filezilla uses TCP and Half-Life server uses UDP, or there is a firewall on the ISP router that UDP packets blocked or fetching this port 27015. This is not a general service.

I'm new to networking, I try to set this up as a challenge, I've learned a lot and read how to do things. Please do not hesitate to point out errors and suggest solutions. If I can't make it, I'll probably try to use ngrok to make the game server work.

Network – TCP handshake too long while running NAT

I have Mikrotik hEX in position & # 39; A & # 39;, Mikrotik hAP AC ^ 2 in position & # 39; B & # 39; installed and connected to OVPN L2. Both routers have the NAT functions activated and the private network.
hEX has the network and hAP the network These two local networks are bound as a local network I have confirmed that all bridge, routing and DHCP policies are configured and working as expected.

After configuring the above setting, I try to connect to a public IP address (& # 39; X & # 39;) from a device connected under hEX in order to use this route.

Terminal -> hEX -> hAP – (NAT) -> remote server & # 39; X & # 39;

To achieve this, I have & # 39; X & # 39; added a routing policy to use the VPN server binding interface IP on hEX as a gateway, and confirmed that the ICMP echo response was well received and stable, and would require a response time of approximately 9-12 ms.

However, when I use software that uses TCP to connect (I haven't confirmed whether it also affects UDP, but I think this is negative), something strange happens as follows:
TCP PSH, ACK is retransmitted for approx. 10 seconds

Even other TCP packets respond as quickly as possible under 50 ms when a TCP connection is established. However, only one TCP ACK packet is answered that SYN answers. The server's ACK is retransmitted for about 10 seconds, and then the handshake process continues. This behavior also occurs when establishing the HTTPS connection and is observed in all devices under hEX.

When I remove the routing policy to address X, I use route

Terminal -> hEX – (NAT) -> Remote Server & # 39; X & # 39 ;, TCP handshake is set up immediately.

If I connect to address X on the device under hAP, use the route

Terminal -> hAP – (NAT) -> Remote Server & # 39; X & # 39 ;, TCP handshake is set up immediately.

What is the problem and how should I fix it?

Networking – Can Double NAT also cause problems, even if it's just a LOCAL NETWORK?

Although I understand that double NAT actually causes problems like port communication, I was wondering whether double NAT can also cause problems in the local network. For further explanation I have a setup …

Enter the image description here

So I have a modem router provided by the ISP, but I don't like to use it, so I use a different router. 2 routers are connected. Servers and clients are connected to my home router. They ping perfectly well. You can easily access each other. I have created a software and the server-client communication works perfectly. However, there is other software that has problems. Clients cannot connect to the server. I was told that it is because it is on double NAT. Now I understand that duplicate NAT is causing problems, but my question is, even if the software is only running on the local network, which means that servers, clients and the home router are the only ones used in software communication ISP routers are used twice NAT with the home router have caused problems in the local network? I mean, the clients accessing the server never had to pass through the ISP router even when it was connected. If there was a problem with double NAT, why is my software working properly? Thank you very much!

azure – I cannot create a NAT gateway

I have a VNet / 16 with 2 subnets / 24 (private and public)

In my public subnet, I have a window with a public IP. I can access these windows with RDP.
In my private subnet I have a Linux without a public IP. I can access this Linux from the public windows using Putty.

Of course, my Linux cannot access the Internet with a private IP. So I need a NAT gateway.

I am trying to deploy a NAT gateway with a new public IP to my private subnet using the Azure web UI:

  1. Public IP creation is fine
  2. The NAT gateway stops with an error: "The resource type was not found in the namespace & # 39; Microsoft.Network & # 39; for the API version & # 39; 2019-09-01 & # 39 ;."

Do you have any idea what happened?

Thank you very much,

Linux – Change the default forwarding policy (VPN / NAT) to be accepted

While reading a tutorial from a very popular hosting provider, I came across something that doesn't seem intuitive. It shows people how to install their own Debian-based OpenVPN server. In particular, the default forwarding policy is changed from "DROP" to "ACCEPT" so that traffic can be forwarded correctly. There seem to be no additional rules anywhere that would restrict routing beyond this standard policy.

If I understand correctly, it can result in someone using the computer as a gateway to the VPN and possibly letting unwanted traffic through. The logic here is that the operating system, without rules that prevent packet forwarding, simply forwards all traffic that is not intended for itself. For example, someone could create a static route for the external IP assuming a network of NAT would normally act as a firewall, but in this case I can only assume that it will rewrite the IP of response packets at best.

This is the tutorial for reference: How to set up an OpenVPN server on Debian 9

I just want to know if my concerns are justified or if I am missing something.

NAT VPS in Hong Kong with IP address for private users or IP address for non-data centers, which is used for TVB TV box streaming

NAT VPS in Hong Kong with IP address for private users or IP address for non-data centers, which is used for TVB TV box streaming Web hosting talk

& # 39);
var sidebar_align = & # 39; right & # 39 ;;
var content_container_margin = parseInt (& # 39; 350px & # 39;);
var sidebar_width = parseInt (& # 39; 330px & # 39;);
// ->

  1. NAT VPS in Hong Kong with IP address for private users or IP address for non-data centers, which is used for TVB TV box streaming

    Hello, I am looking for a NAT VPS in Hong Kong. I bought a domestic HK TV streaming box that I bought back in the US and that doesn't seem to work because it only works in Hong Kong. I tried to host my own OpenVPN software with some Hong Kong VPS providers, but they are all recognized and blocked. My only option is a NAT VPS option in HK, but there doesn't seem to be one that I've found to be reliable and at a good speed. I tried one and the TV box works, but for some reason it is super slow as I suspect these things are shared. Where can I find a NAT vps for HK? I only use it mainly for TV streaming.

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