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Why are IPv4 addresses running out?

The IPv4 Address Shortage According to Vint Cerf (the father of IP), the IPv4 32-bit address size of was chosen arbitrarily. IP was a government/academic collaborative experiment, and the current ...
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36 votes

Why are IPv4 addresses running out?

Ron Maupin's answer gives a brilliant overview of the IPv4 shortage, but I'd like to address this part of your question: Why can't a city (for example) have just one IP address and all homes in ...
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19 votes

why STUN doesn't work with symmetric NAT?

Let's say we have a STUN server at address stun_addr and a server at address srv_addr. Using STUN typically goes something like this: Client connects to the STUN server at stun_addr through NAT ...
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18 votes
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IPv4 Segment 100.64.0.0/10

The 100.64.0.0/10 address block is not private address space; it is shared address space. This is spelled out in RFC 6598, IANA-Reserved IPv4 Prefix for Shared Address Space (I highlighted the ...
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18 votes
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Is there anything stopping me from using Class A addresses on my own network?

As long as you are translating your "15.0.0.0" address space to something unique on the Internet that doesn't overlap, things will "work fine". However, you won't be able to ...
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17 votes

IP addresses from public IP block in my LAN

EDITED I'm assuming you're considering using an IP block that is not registered to you. Otherwise, skip to the last paragraph. Besides being a very poor practice, if you use public addresses on your ...
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16 votes
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Difference between NAT overload and regular NAT?

Strictly speaking, when performing (pure) NAT, only IP addresses are translated, and every internal IP address has to be translated to a different external IP address. This can be a static one-on-one ...
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16 votes

Why are IPv4 addresses running out?

Right now, every home has its own IP address. Why can't a city (for example) have just one IP address and all homes in this city would just be on a private network of that city? Exactly this is ...
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14 votes
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How does NAT share one public IPv4 address across multiple private IPv4 addresses

(For the following I will ignore any DNS lookups or layer two action, since that isn't the relevant part for the NAT story.) Any TCP connection is a tuple of four parts: <source IP> <source ...
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14 votes
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How `UDP Hole Punching` Works?

Details vary but basically it goes something like. The two peers both open a UDP socket bound to a random local port The two peers both contact a server on the internet. This server responds and ...
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14 votes

Could IPv6 make NAT / port numbers redundant?

IPv6 does not have a NAT standard as IPv4 does (NAT breaks the end-to-end premise of IP, and IPv6 was designed to restore that). There is an experimental RFC for IPv6 NAT, but it is a one-to-one NAT ...
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14 votes
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Does NAT violate end to end argument?

It means that IP was designed for each endpoint only to maintain the state of the communications. NAT requires that the NAT device in the middle to maintain a state of the communications. IP was ...
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13 votes

Why does NAT translate a source port?

First, I'm assuming you're focused on TCP. UDP has some differences, and I'm not as up-to-speed on that part. I’m beginning to learn about nat and I was wondering why does NAT translate a source ...
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13 votes
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Why is symmetric NAT called "symmetric"?

tl;dr It comes from STUN and is symmetric because it identifies a 1:1 relationship between NAT mapping and L4 flow. The name symmetric NAT is as far as I know introduced by the original STUN RFC 3489, ...
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12 votes
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NEWBIE: How can two computers communicate if they are behind firewalls?

First: What you describe is NAT, not firewalling. A firewall just filters what can go through, a NAT device changes addresses in packets. You almost answer the first question yourself. Yes, a NAT ...
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How does the router know how to route the packets to my terminal?

NAT If you are using static (one-to-one) NAT, the router will assign the 11.2.10.172 public IP to the first PC ( for example 192.168.1.101 ) trying to reach google.com. In this case, the two PC will ...
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12 votes
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How is NAT a hack?

Before NAT every device connected to the internet had its own IP address. That was how the internet was designed. This gives you great flexibility and visibility. If you have a firewall then it can ...
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12 votes
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IPv6 and online privacy and security

Let's look at a live example. This being from my Linux workstation. (And for simplicity I actually omitted a couple of addresses.) I'll explain each of the addresses in turn: $ ip a s dev br0 3: br0: &...
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How does NAT Stitching work?

You must remember that a flow using NAT will look like two different flows: a flow pre-NAT, and a flow post-NAT. This is because NAT is changing one or more of the addresses in the packets. This can ...
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11 votes
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Ping a private IP address in another network

A PC in a private IP range can't be acccesed from the public internet. Devices in private range connecting to internet use a proxy or router/NAT device that replaces the local source IP for a single ...
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11 votes

Is there anything stopping me from using Class A addresses on my own network?

Any network addresses you use in your own company that are in use or assigned to a different company on the public Internet will be inaccessible to your users trying to reach those addresses on the ...
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11 votes

routing between vlans not working

You don't have NAT enabled (you don't have ip nat outside on Vl 20). Without NAT, the ISP doesn't know how to route back to your 192.9.200.0 network. If you NAT to the VLan 20 address, the ISP ...
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10 votes
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How NAT / PortForwarding / TCP/IP works?

There is a general misconception between NAT (Network address translation) and PAT (Port Address Translation), which is what we mostly use in our home routers. NAT Let's assume we have a network with ...
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What is the purpose of subnetting, if we have NAT?

NAT and subnetting solve two different problems. Problem 1: Previously IP addresses were divided into classes A, B and C. A class C address had a default subnet mask of 255.255.255.0 meaning 24 bits ...
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How are IPv4 Addresses provided uniquely to domains?

Who mainly provides IP addresses to domains? As in, who commands, "www.google.com, 103.233.38.93 is yours; www.stackexchange.com I will assign 104.16.115.182 to you; etc." Normally IP addresses are ...
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10 votes
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At which layer does router operate?

Network address translation (NAT) is a feature of Router which is required for routing traffic. That is completely incorrect. NAT is a kludge (a clumsy, inefficient solution) designed to extend the ...
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9 votes

60 devices on a /29 network

Are you absolutely positive that all 60 devices need to have their own public WAN IP address? The ISP is giving you the globally reachable IP addresses for internet connectivity. You can have well ...
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9 votes
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How does NAT decide which connections are inbound, and which are outbound?

TCP is a connection-oriented protocol, and it can only communicate through connections. Before you start programming using TCP, it would be helpful to first understand how TCP works, and you should ...
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9 votes
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How does UDP NAT Know When To Remove The Rule

A NAT router doesn't know when to remove a UDP mapping - it guesses. The router simply ages (or times) out the entry when it hasn't been used for a period of time (usually between 5 and 60 minutes). ...
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9 votes

Could IPv6 make NAT / port numbers redundant?

One drawback is that the upper layers would need to be aware of IP addresses, which sort of violates the layering principle. What would then happen if you switched to IPv4? Or something else? How ...
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