Question about Internet, IPv4, and NAT.

brickwall99

Hello all.

I already have my network+ certification, but I have a question I'm sure someone can answer for me. I'm training for a new position at my job and it gives me almost as many questions as it does answers lol Anyway, here is my question.

What I believe I understand:
So from what I understand the reason (main reason anyway) IPv6 was created was because we are running out of IPv4 addresses for use on the internet, right? I know that a class a network can address up to 16,777,216 addresses. With various different technologies and protocols such as NAT we are able to make a single IP address much more efficient for use within a large network such as what a business, school, etc. would use.

So what I am wondering, with NAT and everything else, why are we running out of IPv4 addresses? Can't we just use more routers and create more networks to provide more addresses?

I'm by no means an "expert" in the networking field, I understand the basics pretty well, but I'm having a hard time wrapping my head around this. I'm sure if it were possible it would have been done and we wouldn't be running in to this limitation. I'm sure we are using IPv4 as efficiently as humanly possible and yet we are still running out of addresses, which is why we needed something like IPv6.

For an oversimplified example, let's say you have Internet Router A, using a class A network, and it hands out IP Addresses to ISPs, government agencies, etc. When it nears the 16million limit, why not just create another network, Internet Router B, with NAT to get ~16 million more addresses, and repeat as necessary? Wouldn't this create a virtual limitless number of IP Addresses for use on the internet? I mean basically that's the reason a huge corporation can get by with just a handful of addresses, yet have thousands and thousands of devices on it's network, right?

I think I explained that right, hope I didn't confuse anyone. lol If not I'm sure someone can enlighten me.

Thanks in advance!

Darril

First, you're correct about IPv6. It was created because the Internet was running out of IPv4 addresses. Additionally, the routing tables were becoming overloaded. This was only a problem on the Internet, not internal networks.

One of the things you might want to separate is public and private addresses. Any address on the Internet is a public address. Addresses for companies are almost always private addresses.

A public IP address must be unique on the Internet. In other words, you can't have any two hosts on the Internet with the same IP address. If public IP addresses aren't unique, you'll have conflicts and routers won't be able to route the traffic to the correct hosts. With 32 bits you could theoretically get 4 billion IP addresses but due to a lot of waste, you don't even have that many.

No matter how you slice it, 32 bits (2 raised to the 32 power) only gives you 4 billion addresses. Early in the design, they thought that would be more than enough. With the explosion of the Internet, it has become apparent that 4 billion addresses isn't enough for the future. IPv6 is 128 bits (2 raised to the 128th power) which should last quite a while.

A private IP address must be unique within a company's network. In other words, you can't use 192.168.1.1 more than twice within a company's private network.

However, since private addresses are private, any company can use the same private addresses as another company. For example, xyz inc can use 192.168.1.1 and abc inc can also use 192.168.1.1.

In short, companies weren't running out of private addresses. There was only a shortage or potential shortage of public IP addresses.

On NAT, it is used to translate public IP addresses to private IP addresses and back. A company could have 1,000 internal clients. They'd have 1,000 private IP addresses but only need one or two public IP addresses. Companies often use a proxy server with NAT installed to translate public and private IPs.

If you have a home network with a wireless router, it probably has NAT installed. Your internal computers have private IPs. The router is issued a public IP on the WAN connection from the ISP. The router than uses NAT to translate private to public IPs and provide access to the Internet.

HTH,

Darril Gibson
Author: CompTIA Security+: Get Certified Get Ahead
ISBN-10: 1439236364
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