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In this organization, all servers and personal computers that I have worked on have a static IP belonging to the Public address space assigned to it. There must be NAT-based firewall/s as my external IP address differs from the local one.

As this is a big organization with many nodes I can see why they choose a public IP over a private IP for nodes on the private network.. These addresses would technically never be Illegal addresses as they are assigned by InterNIC to just this organization.

So, why go through the expense of registering all those IP addresses when there is a NAT in use (probably for most of the private addresses)..?

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closed as not constructive by Brad Patton, Tog, 8088, Hennes, davidgo May 10 '13 at 8:43

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I guess the solution followed by this organization is not a 'best practice' and so was too specific to be helpful to the general audience. I guess that's why this question has been closed, but the below discuss has partially answered by question so its cool. Thanks! –  Kent Pawar May 10 '13 at 9:21

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You don't have to register them all. You can lease a block of address. Before natting companies would purchase entire blocks of IP addresses. Then one day we realized we were running out and we started using NAT. Now it's hard to purchase an entire block of addresses. The military and some big corporations use class A address blocks. You can get over 16 million hosts out of a Class A.

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Thanks @Jason - but since this organization has already leased a large set of Public IPs, I am trying to figure out why it is more convenient to do so even though there is a burden of cost..? –  Kent Pawar May 9 '13 at 14:22
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Balance the cost with the risk of changing things as well the chance to successfully acquire 'real' IP later on and you might have part of the answer. A potential second reason is that someone ordered them to use NAT 'for security' (even though NAT really is not designed for that and proper firewall rules would work just as well and with less headaches). –  Hennes May 9 '13 at 18:08
    
Thanks @Hennes - so basically they won't have to worry about making a host a edge as it already has a Public IP and NAT along with the firewall hides the rest of the host and possibly prevents all inbound connections initiated by host outside the network. –  Kent Pawar May 10 '13 at 9:19
    
Kind of. You still wouldn't want to put a host on the edge of the net even if it has its own firewall. IF I'm reading your statement right. You would still want an enterprise level firewall and one place for all your inbound and outbound traffic to flow. That way you still have some place to monitor everything. Just like Hennes said, NAT isn't for security, it was to fix our limited IPv4 space issue. –  Jason H May 10 '13 at 10:18

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