9 Network Address Translation
This chapter covers
- Private IPv4 addresses
- Using NAT to translate between private and public IPv4 addresses
- The different types of NAT
- Configuring NAT on Cisco routers
IPv4 address exhaustion is a major problem and has been for a long time. In chapters 20 and 21 of volume 1, we covered the long-term solution: IPv6. However, IPv4 is still dominant to this day thanks to a few solutions that have been very effective in extending IPv4’s lifespan. We covered one of these solutions in chapter 11 of volume 1 on subnetting with Classless Inter-Domain Routing (CIDR), which allows more flexibility than the rigid classful addressing system that came before it.
In this chapter, we will cover two more important solutions that, combined, have proven essential in preserving the IPv4 address space: private IPv4 addressing and Network Address Translation (NAT). Three ranges of IPv4 addresses have been reserved for free use in private networks without the need to be globally unique, and NAT provides a way to translate those private addresses into public addresses for communication over the internet. We will cover the following two CCNA exam topics:
- 1.7 Describe the need for private IPv4 addressing
- 4.1 Configure and verify inside source NAT using static and pools