NAT test

4. What are three advantages of using private IP addresses and NAT? (Choose three.)

• hides private LAN addressing from outside devices that are connected to the Internet

• permits LAN expansion without additional public IP addresses

• reduces CPU usage on customer routers

• creates multiple public IP addresses

• conserves registered public IP addresses

Answer explanation

Explanation: Private IP addresses are designed to be exclusively used for internal networks and they cannot be used on the Internet. Thus they are not visible directly from the Internet and they can be used freely by network administrators for internal networks. In order for the internal hosts to access the Internet, NAT is used to translate between private and public IP addresses. NAT takes an internal private IP address and translates it to a global public IP address before the packet is forwarded.

16. What command would be used as part of configuring NAT or PAT to clear dynamic entries before the timeout has expired?

• clear ip dhcp
• clear ip nat translation
• clear access-list counters
• clear ip pat statistics

18. Refer to the exhibit. A technician is configuring R2 for static NAT to allow the client to access the web server. What is a possible reason that the client PC cannot access the web server?

• The IP NAT statement is incorrect.

• Interface Fa0/1 should be identified as the outside NAT interface.

• Interface S0/0/0 should be identified as the outside NAT interface.

• The configuration is missing a valid access control list.

Answer explanation

Explanation: Interface S0/0/0 should be identified as the outside NAT interface. The command to do this would be R2(config-if)# ip nat outside.

19. In setting up a small office network, the network administrator decides to assign private IP addresses dynamically to workstations and mobile devices. Which feature must be enabled on the company router in order for office devices to access the internet?

• UPnP

• MAC filtering

• NAT

• QoS

Answer explanation

Explanation: Network Address Translation (NAT) is the process used to convert private addresses to internet-routable addresses that allow office devices to access the internet.

35. What command would be used as part of configuring NAT or PAT to display information about NAT configuration parameters and the number of addresses in the pool?

• show running-config
• show ip nat statistics
• show ip cache
• show version

39. Refer to the exhibit. R1 is configured for NAT as displayed. What is wrong with the configuration?

• NAT-POOL2 is not bound to ACL 1.

• Interface Fa0/0 should be identified as an outside NAT interface.

• The NAT pool is incorrect.

• Access-list 1 is misconfigured.

Answer explanation

Explanation: R1 has to have NAT-POOL2 bound to ACL 1. This is accomplished with the command R1(config)#ip nat inside source list 1 pool NAT-POOL2. This would enable the router to check for all interesting traffic and if it matches ACL 1 it would be translated by use of the addresses in NAT-POOL2.

65. Refer to the exhibit. A PC at address 10.1.1.45 is unable to access the Internet. What is the most likely cause of the problem?

• The NAT pool has been exhausted.

• The wrong netmask was used on the NAT pool.

• Access-list 1 has not been configured properly.

• The inside and outside interfaces have been configured backwards.

Answer explanation

Explanation: The output of show ip nat statistics shows that there are 2 total addresses and that 2 addresses have been allocated (100%). This indicates that the NAT pool is out of global addresses to give new clients. Based on the show ip nat translations, PCs at 10.1.1.33 and 10.1.1.123 have used the two available addresses to send ICMP messages to a host on the outside network.

82. Refer to the exhibit. What is the purpose of the command marked with an arrow shown in the partial configuration output of a Cisco broadband router?

• defines which addresses are allowed into the router

• defines which addresses can be translated

• defines which addresses are assigned to a NAT pool

• defines which addresses are allowed out of the router

87. Refer to the exhibit. An administrator is trying to configure PAT on R1, but PC-A is unable to access the Internet. The administrator tries to ping a server on the Internet from PC-A and collects the debugs that are shown in the exhibit. Based on this output, what is most likely the cause of the problem?

• The inside and outside NAT interlaces have been configured backwards

• The inside global address is not on the same subnet as the ISP

• The address on Fa0/0 should be 64.100.0.1.

• The NAT source access list matches the wrong address range.

Answer explanation

Explanation: The output of debug ip nat shows each packet that is translated by the router. The “s” is the source IP address of the packet and the “d” is the destination. The address after the arrow (“->”) shows the translated address. In this case, the translated address is on the 209.165.201.0 subnet but the ISP facing interface is in the 209.165.200.224/27 subnet. The ISP may drop the incoming packets, or might be unable to route the return packets back to the host because the address is in an unknown subnet.