44. NAT (STATIC): PART 1

PRIVATE IPv4 ADDRESSES (RFC 1918)

IPv4 doesn’t provide enough ADDRESSES for all DEVICES that need an IP ADDRESS in the modern world
The long-term solution is to switch to IPv6
There are THREE MAIN short-term solutions:
- CIDR
- PRIVATE IPv4 ADDRESS
- NAT

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

You are free to use these ADDRESSES in your NETWORKS. They don’t have to be GLOBALLY UNIQUE

INTRO TO NAT

NETWORK ADDRESS TRANSLATION (NAT) is used to modify the SOURCE and / or DESTINATION IP ADDRESSES of packets
There are various reasons to use NAT, but the MOST common reason is to ALLOW HOSTS with PRIVATE IP ADDRESSES to communicate with other HOSTS over the INTERNET
For the CCNA you have to understand SOURCE NAT and how to configure it on CISCO ROUTERS

STATIC NAT

STATIC NAT involves statically configuring ONE-TO-ONE MAPPINGS of PRIVATE IP ADDRESSES to PUBLIC ADDRESSES

PRIVATE IP CANNOT BE MAPPED TO THE SAME GLOBAL IP

THE SECOND MAPPING WILL BE REJECTED

STATIC NAT CONFIGURATIONS

Command clear ip nat translation

Command show ip nat statistics

COMMAND REVIEW