Network Address Translation Questions and Answers

Answer: B

Correct answer: prefix-length

The pool can be defined either as netmask 255.255.255.0 or as prefix-length 24 - the two are equivalent and one or the other must appear. Slash notation is not accepted in this command, and block-size belongs to wireless configuration rather than to NAT.

Answer: B

The show ip nat statistics command displays a summary of the NAT configuration as well as counts of active translation types, hits to an existing mapping, misses (causing an attempt to create a mapping), and expired translations.

Answer: C

Correct answer: debug ip nat

debug ip nat prints each translation as it is created and used, so it shows the process happening rather than the table that resulted. That makes it the tool when the question is why a particular flow is not being translated - and, as always with debug on a busy router, it should be enabled briefly and with the output directed somewhere it can be read.

Answer: A

As in access-lists, you must configure your interfaces before NAT will provide any translations. On the inside networks you would use the command ip nat inside. On the outside interface, you will use the command ip nat outside.

Answer: B

The command ip nat pool  creates the pool that hosts can use to get onto the global Internet. What makes option B correct is that the range 171.16.10.65 through 171.16.10.94 includes 30 hosts, but the mask has to match 30 hosts as well, and that mask is 255.255.255.224. Option C is wrong because the pool name has a lower case "T" in the pool name. Pool name's are case sensitive.

Answer: C

Correct answer: NAT Overload

Port Address Translation and NAT Overload are the same thing under two names: many inside hosts share one global address, distinguished by the source port the router assigns to each session. It is what allows an entire site to sit behind a single public address, and it is by far the most common form of NAT in use.

Answer: A

Correct answer: 1, 2 and 4

All three are standard reasons: private addressing behind a public one, renumbering avoided when changing ISP by translating at the boundary, and merging two intranets whose address ranges overlap. Statement 3 is not a NAT use - if no host is to reach the internet, the answer is not to route or to filter, not to translate.

Answer: A

Correct answer: 1, 3 and 5

The genuine disadvantages are the switching delay translation adds, the loss of end-to-end traceability since the original source is hidden, and the applications that break because they carry addresses inside the payload - older FTP, SIP and IPSec among them. Statements 2, 4 and 6 are advantages of NAT rather than drawbacks, and are there to be sorted out.