44. NAT (Static)

Private IPv4 Addresses (RFC 1918)

The IPv4 addressing scheme does not provide enough addresses for all devices requiring an IP address in today’s digital landscape.
The long-term solution is transitioning to IPv6. However, there are three primary short-term solutions:
- CIDR (Classless Inter-Domain Routing)
- Private IPv4 Addresses
- NAT (Network Address Translation)

RFC 1918 Private Address Ranges

RFC 1918 specifies the following IPv4 address ranges as private:

10.0.0.0 /8       (10.0.0.0 to 10.255.255.255)             CLASS A 
172.16.0.0 /12    (172.16.0.0 to 172.31.255.255)           CLASS B
192.168.0.0 /16   (192.168.0.0 to 192.168.255.255)         CLASS C

These addresses can be freely used within your networks and do not need to be globally unique.

Introduction to NAT

Network Address Translation (NAT) is a method used to modify the source and/or destination IP addresses of packets as they pass through a router or firewall.

Common Uses of NAT

The most common application of NAT is to allow hosts with private IP addresses to communicate with other hosts over the Internet.
For the CCNA certification, it’s essential to understand Source NAT and how to configure it on Cisco routers.

Static NAT

Static NAT involves configuring one-to-one mappings between private IP addresses and public addresses. This means that each private IP address has a fixed corresponding public IP address.