Understanding Network,Address Translation

Understanding Network
Address Translation
Let’s talk about the history behind NAT. It was first implemented in Cisco IOS release 11.2 and
is defined in RFC 1631 and RFC 3022 as a way to alleviate the depletion of the IPv4 address space.
It is a temporary workaround to the immediate problem of too many hosts and not enough IP
addresses. It is a kludge that breaks the rules of IP, which creates other problems. For example,
when you used IPSec to protect your traffic, it was incompatible with NAT until Cisco found a
workaround, but even this has its problems. This is what I call a kludge to fix another kludge.
RFC 1918 was created to set aside a number of IP addresses for people to use inside their networks.
It set aside the following ranges of IP addresses:

10.0.0.0 to 10.255.255.255 or 10.0.0.0/8

172.16.0.0 to 172.31.255.255 or 172.16.0.0/12

192.168.0.0 to 192.168.255.255 or 192.168.0.0/16
These IP addresses will never appear in the global routing table, and so they can be used by
organizations for their private internal intranets. Multiple companies can use the 10.0.0.0/8
address space within their own networks, so theoretically, there’s an unlimited supply of IP
addresses. If these IP addresses are not going to be globally unique, how can hosts from these
networks communicate across the Internet? They must be translated, and this is where NAT
comes into play. NAT also can be used when two networks are merged and they both use the
same address space.