Network Address Translation Questions and Answers

Q: Which are considered the methods of NAT? 1.Static 2.IP NAT pool 3.Dynamic 4.NAT double-translation 5.Overload

Correct answer: 1, 3 and 5The three methods are static, mapping one inside address to one global address permanently; dynamic, drawing from a pool as sessions arise; and overload, sharing one address by port. An IP NAT pool is a component used by the dynamic and overload methods rather than a method in itself, and double translation is not a Cisco NAT mode.

Q: Which command will allow you to see real-time translations on your router?

Correct answer: debug ip natdebug 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.

Q: Which of the following would be good reasons to run NAT? 1.You need to connect to the Internet and your hosts don't have globally unique IP addresses. 2.You change to a new ISP that requires you to renumber your network. 3.You don't want any hosts connecting to the Internet. 4.You require two intranets with duplicate addresses to merge.

Correct answer: 1, 2 and 4All 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.

Q: Which of the following is considered to be the address before translation?

Correct answer: Inside localThe inside local address is what the inside host is actually configured with - typically an RFC 1918 private address - before any translation occurs. Read the terms consistently: inside means the host belongs to your network, and local means the address as it is seen from inside it.

Q: Which of the following are disadvantages of using NAT? 1.Translation introduces switching path delays. 2.Conserves legally registered addresses. 3.Causes loss of end-to-end IP traceability. 4.Increases flexibility when connecting to the Internet. 5.Certain applications will not function with NAT enabled. 6.Reduces address overlap occurrence.

Correct answer: 1, 3 and 5The 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.

Q: Which of the following is considered to be the destination host after translation?

Correct answer: Outside globalAfter translation the destination is referred to by its address on the outside network - the real, registered address of the outside host. Together with the previous items this completes the set: inside local and inside global for your own host before and after, outside local and outside global for the far host before and after.

Q: Which command will create a dynamic pool named Todd that will provide you with 30 global addresses?

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.

Q: Which command will clear all the translations active on your router?

Correct answer: clear ip nat translations *The asterisk clears every dynamic entry in the table, which is the usual way of forcing translations to be rebuilt after a configuration change - a stale entry will otherwise persist until its timeout. A specific entry can be cleared by giving its addresses instead, and static translations are removed by deleting their configuration rather than by this command.

11.

Which are considered the methods of NAT?

1.Static

2.IP NAT pool

3.Dynamic

4.NAT double-translation

5.Overload

A.1 and 6
B.3 only
C.1, 3 and 5
D.All of the above

Answer: C

Correct answer: 1, 3 and 5

The three methods are static, mapping one inside address to one global address permanently; dynamic, drawing from a pool as sessions arise; and overload, sharing one address by port. An IP NAT pool is a component used by the dynamic and overload methods rather than a method in itself, and double translation is not a Cisco NAT mode.

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12.

Which command will allow you to see real-time translations on your router?

A.show ip nat translations
B.show ip nat statistics
C.debug ip nat
D.clear ip nat 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.

Discuss in Forum

13.

Which of the following would be good reasons to run NAT?

1.You need to connect to the Internet and your hosts don't have globally unique IP addresses.

2.You change to a new ISP that requires you to renumber your network.

3.You don't want any hosts connecting to the Internet.

4.You require two intranets with duplicate addresses to merge.

A.1, 2 and 4
B.2 and 4
C.3 only
D.All of the above

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.

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14.

Which of the following are advantages of using NAT?

1.Translation introduces switching path delays.

2.Conserves legally registered addresses.

3.Causes loss of end-to-end IP traceability.

4.Increases flexibility when connecting to the Internet.

5.Certain applications will not function with NAT enabled.

6.Reduces address overlap occurrence.

A.1, 3 and 4
B.3, 5 and 6
C.5 and 6
D.2, 4 and 6

Answer: D

NAT is not perfect, but there are some advantages. It conserves global addresses, which allow us to add millions of hosts to the Internet without "real" IP addresses. This provides flexibility in our corporate networks. NAT can also allow you to use the same subnet more than once in the same network without overlapping networks.

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15.

Which of the following is considered to be the address before translation?

A.Inside local
B.Outside local
C.Inside global
D.Outside global

Answer: A

Correct answer: Inside local

The inside local address is what the inside host is actually configured with - typically an RFC 1918 private address - before any translation occurs. Read the terms consistently: inside means the host belongs to your network, and local means the address as it is seen from inside it.

Discuss in Forum

16.

Which of the following are disadvantages of using NAT?

1.Translation introduces switching path delays.

2.Conserves legally registered addresses.

3.Causes loss of end-to-end IP traceability.

4.Increases flexibility when connecting to the Internet.

5.Certain applications will not function with NAT enabled.

6.Reduces address overlap occurrence.

A.1, 3 and 5
B.3 and 4
C.2, 4 and 5
D.1 and 3

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.

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17.

Which of the following is considered to be the destination host after translation?

A.Inside local
B.Outside local
C.Inside global
D.Outside global

Answer: D

Correct answer: Outside global

After translation the destination is referred to by its address on the outside network - the real, registered address of the outside host. Together with the previous items this completes the set: inside local and inside global for your own host before and after, outside local and outside global for the far host before and after.

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18.

Which command will create a dynamic pool named Todd that will provide you with 30 global addresses?

A.ip nat pool Todd 171.16.10.65 171.16.10.94 net 255.255.255.240
B.ip nat pool Todd 171.16.10.65 171.16.10.94 net 255.255.255.224
C.ip nat pool todd 171.16.10.65 171.16.10.94 net 255.255.255.224
D.ip nat pool Todd 171.16.10.1 171.16.10.254 net 255.255.255.0

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.

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19.

Which command will clear all the translations active on your router?

A.show ip nat translations
B.show ip nat statistics
C.debug ip nat
D.clear ip nat translations *

Answer: D

Correct answer: clear ip nat translations *

The asterisk clears every dynamic entry in the table, which is the usual way of forcing translations to be rebuilt after a configuration change - a stale entry will otherwise persist until its timeout. A specific entry can be cleared by giving its addresses instead, and static translations are removed by deleting their configuration rather than by this command.

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