NAT/PAT Questions

Question 1

A technician is configuring a static NAT. Which of the following statements are correct?

A. a static NAT always exists in the NAT table
B. hosts from outside cannot initiate the connection
C. hosts from outside can initiate the connection
D. static NAT does not need to configure inside and outside NAT interfaces

Answer: A B

Explanation

With static NAT, translations exist in the NAT translation table as soon as you configure static NAT command(s), and they remain in the translation table until you delete the static NAT command(s) -> A is correct.

With dynamic NAT, translations do not exist in the NAT table until the router receives traffic that requires translation. Dynamic translations have a timeout period after which they are purged from the translation table.

Because static NAT translations are always present in the NAT table so outside hosts can initiate the connection without being dropped -> B is correct, C is not correct.

Static translations can not be configured with access lists. To configure static NAT, we only need to specify source IP, NAT IP, inside interface & outside interface.

We have to specify which is the inside and outside interface -> D is not correct.

For your information, below is an example of configuring static NAT:

R0(config)#int f0/0
R0(config-if)#ip nat inside

R0(config-if)#int f0/1
R0(config-if)#ip nat outside

R0(config)#ip nat inside source static 10.0.0.1 200.0.0.2

(Reference: http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f31.shtml)

Question 2

A colleague is asking why he should implement NAT to his network. What will you tell him about NAT? (Choose two)

A. NAT increases network security as inside networks are not advertised to outside
B. NAT does not alter the packets before sending them to the outside
C. With NAT configured, hosts do not need to reassign IP address for access from outside
D. NAT replaces the original MAC addresses with a predefined MAC address
E. NAT increases the routing speed

Answer: A C

Explanation

By not reveal the internal IP addresses, NAT adds some security to the inside network -> A is correct.

NAT has to modify the source IP addresses in the packets -> B is not correct.

By allocating specific public IP addresses to inside hosts, NAT eliminates the need to re-address the inside hosts -> C is correct.

NAT only alters the source IP address, not the MAC addresses -> D is not correct.

NAT does not increase the routing speed. In fact NAT reduces the routing speed as it needs to proceed the IP addresses in the packets.

Question 3

Which of the following statements is correct about the command “ip nat inside source list 50 interface serial0/1 overload”?

A. The configuration is missing a pool for NAT
B. There is not enough public IP addresses to allocate for inside hosts
C. Number 50 is the access-list number
D. The keyword “overload” in the ip nat inside source command allow 1:1 IP translation

Answer: C

Explanation

The “list 50″ refers to the access-list number 50.