Network Address Translation (10.2)–Cisco IPv4 and IPv6 Address Management
The number of public IPv4 addresses is severely limited, which was one of the primary reasons for RFC 1918 private IPv4 addresses. NAT for IPv4 provides for the translation between private and public IPv4 addresses.
Video—Introduction to NAT (10.2.1)
Refer to the online course to view this video.
NAT Operation (10.2.2)
The wireless router receives a public address from the ISP, which allows it to send and receive packets on the Internet. It, in turn, provides private addresses to local network clients. Because private addresses are not allowed on the Internet, a process is needed for translating private addresses into unique public addresses to allow local clients to communicate on the Internet.
The process used to convert private addresses to Internet-routable addresses is called Network Address Translation (NAT). With NAT, a private (local) source IPv4 address is translated to a public (global) address. The process is reversed for incoming packets. The wireless router is able to translate many internal IPv4 addresses to the same public address by using NAT.
Only packets destined for other networks need to be translated. These packets must pass through the gateway, where the wireless router replaces the private IPv4 address of the source host with its own public IPv4 address.
Although each host on the internal network has a unique private IPv4 address assigned to it, the hosts must share the single Internet-routable address assigned to the wireless router.
In Figures 10-3 and 10-4, a home router translates packets using NAT.
Figure 10-3 Wireless Router Using NAT to Translate Outbound Traffic
Figure 10-4 Wireless Router Using NAT to Translate Inbound Traffic
Packet Tracer—Examine NAT on a Wireless Router (10.2.3)
In this activity, you will complete the following objectives:
- Examine NAT configuration on a wireless router.
- Set up four PCs to connect to a wireless router using DHCP.
- Examine traffic that crosses the network using NAT.
IPv4 Issues (10.3)
IPv4 was designed in the 1970s and implemented in 1980. Since then, the number of devices that access the Internet has increased substantially, beyond the 4.3 billion IPv4 addresses.
Need for IPv6 (10.3.1)
You already know that IPv4 is running out of addresses. That is why you need to learn about IPv6.
IPv6 is designed to be the successor to IPv4. IPv6 has a larger, 128-bit address space, providing 340 undecillion (that is, 340 followed by 36 zeros) possible addresses. However, IPv6 is more than just a larger address space.
When the IETF began its development of a successor to IPv4, it used this opportunity to fix the limitations of IPv4 and include enhancements. One example is Internet Control Message Protocol version 6 (ICMPv6), which includes address resolution and address autoconfiguration not found in ICMP for IPv4 (ICMPv4) and IPv6 addresses (ICMPv6).
The depletion of IPv4 address space has been the motivating factor for moving to IPv6. As Africa, Asia, and other areas of the world become more connected to the Internet, there are not enough IPv4 addresses to accommodate this growth. As shown in Figure 10-5, all five Regional Internet Registries (RIRs) have run out of IPv4 addresses.
Figure 10-5 RIR IPv4 Exhaustion Dates
As noted previously, IPv4 has a theoretical maximum of 4.3 billion addresses. Private addresses, in combination with Network Address Translation (NAT), have been instrumental in slowing the depletion of IPv4 address space. However, NAT is problematic for many applications, creates latency, and has limitations that severely impede peer-to-peer communications.
With the ever-increasing number of mobile devices, mobile providers have been leading the way with the transition to IPv6. The top two mobile providers in the United States report that over 90 percent of their traffic is over IPv6.
Most top ISPs and content providers such as YouTube, Facebook, and Netflix have also made the transition. Many companies like Microsoft, Facebook, and LinkedIn are transitioning to IPv6-only internally. In 2020, US broadband ISP Comcast reported an IPv6 deployment of over 74 percent, and the country of India is now over 62 percent.
Internet of Things
The Internet of today is significantly different than the Internet of past decades. The Internet of today is more than email, web pages, and file transfers between computers. The evolving Internet includes an Internet of Things (IoT). No longer will the only devices accessing the Internet be computers, tablets, and smartphones. The sensor-equipped, Internet-ready devices will include everything from automobiles and biomedical devices to household appliances and lighting systems.
With an increasing Internet population, a limited IPv4 address space, issues with NAT, and the IoT, now is the time to transition to IPv6.