Explain the basic operation of NAT. CCIE Course Training in Gurgaon

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network.
You need to merge two intranets with duplicate addresses.
You typically use NAT on a border router. For an illustration of this, see Figure 7.4.
Now you may be thinking, “NAT’s totally cool. It’s the grooviest greatest network gadget,
and I just gotta have it.” Well, hang on a minute. There are truly some serious snags related
to NAT use. Oh—don’t get me wrong: It really can save you sometimes, but there’s a dark side
you need to know about, too. For a visual of the pros and cons linked to using NAT, check
out Table 7.2.
7.6 Explain the basic operation of NAT 341
FIGURE 7 . 4 Where to configure NAT
The most obvious advantage associated with NAT is that it allows you to conserve
your legally registered address scheme. This is why we haven’t run out
of IPv4 addresses—think about it.
Types of Network Address Translation
In this section, I’m going to go over the three types of NAT:
Static NAT This type of NAT is designed to allow one-to-one mapping between local and
global addresses. Keep in mind that the static version requires you to have one real Internet
IP address for every host on your network.
TABLE 7 . 2 Advantages and Disadvantages of Implementing NAT
Advantages Disadvantages
Conserves legally registered addresses. Translation introduces switching path delays.
Reduces address overlap occurrence. Loss of end-to-end IP traceability.
Increases flexibility when connecting to
Internet.
Certain applications will not function with
NAT enabled.
Eliminates address renumbering as
network changes.
342 Chapter 7 Implement, verify, and troubleshoot NAT and ACLs
Dynamic NAT This version gives you the ability to map an unregistered IP address to a registered
IP address from out of a pool of registered IP addresses. You don’t have to statically
configure your router to map an inside to an outside address as you would using static NAT,
but you do have to have enough real, bona fide IP addresses for everyone who’s going to be
sending packets to and receiving them from the Internet.
Overloading This is the most popular type of NAT configuration. Understand that overloading
really is a form of dynamic NAT that maps multiple unregistered IP addresses to a single
registered IP address—many-to-one—by using different ports. Now, why is this so special?
Well, because it’s also known as Port Address Translation (PAT). And by using PAT (NAT
Overload), you get to have thousands of users connect to the Internet using only one real
global IP address—pretty slick, yeah? Seriously, NAT Overload is the real reason we haven’t
run out of valid IP address on the Internet. Really—I’m not joking.
Exam Objectives
Remember the best advantage to using Network Address Translation The largest advantage
to using NAT on your network is that it conserves legally registered addresses.
Remember the three types of NAT. The three types of NAT are static, dynamic, and
NAT overload.