CCNA 2 Routing and Switching Essentials v5 Chapter 11: Network Address Translation for IPv4 – Check Your Understanding Questions Answers
1. Refer to the following output. Based on the output, which statement is true about the NAT configuration?
- Static NAT is configured.
- Dynamic NAT is configured.
- NAT Overload (PAT) is configured.
- NAT is configured incorrectly.
Explanation: Because port numbers are shown beside the IP addresses in the NAT translations, PAT is being used.
2. What is the default timeout value for NAT translations?
- One hour
- One day
- One week
- Indefinite
Explanation: NAT translations time out after 24 hours. This value can be modified. NAT timeout values are configured in seconds. 86,400 seconds equals 24 hours.
3. Match the characteristic to the NAT technique. Note that a technique can have more than one characteristic.
- Provides one-to-one fixed mappings of local and global addresses
- Assigns the translated address of IP hosts from a pool of public addresses
- Can map multiple addresses to a single address of an external interface
- Assigns unique source port numbers of an inside global address on a session- by-session basis
- Allows an external host to establish sessions with an internal host
_______ Dynamic NAT
_______ PAT
_______ Static NAT
| Assigns the translated address of IP hosts from a pool of public addresses. | Dynamic NAT |
| Can map multiple addresses to a single address of an external interface. Assigns unique source port numbers of an inside global address on a session- by-session basis. |
PAT |
| Provides one-to-one fixed mappings of local and global addresses. Allows an external host to establish sessions with an internal host. |
Static NAT |
4. Consider the following configuration:
R2(config)# ip nat inside source static 192.168.0.100 209.165.200.2 R2(config)# interface serial0/0/0 R2(config-if)# ip address 10.1.1.2 255.255.255.252 R2(config-if)# ip nat inside R2(config-if)# exit R2(config)# interface serial0/1/0 R2(config-if)# ip address 209.165.200.225 255.255.255.224 R2(config-if)# ip nat outside R2(config-if)# exit
Which host(s) will be translated by NAT?
- 10.1.1.2
- 192.168.0.100
- 209.165.200.2
- All hosts on the 10.1.1.0 network
- All hosts on the 192.168.0.0 network
Explanation: The host with the address 192.168.0.100 will be translated into 209.165.200.2.
5. Consider the following configuration:
R2(config)# ip nat pool nat-pool1 209.165.200.225 209.165.200.240 netmask 255.255.255.0 R2(config)# ip nat inside source list 1 pool nat-pool1 R2(config)# interface serial0/0/0 R2(config-if)# ip address 10.1.1.2 255.255.255.252 R2(config-if)# ip nat inside R2(config-if)# exit R2(config)# interface serial0/1/0 R2(config-if)# ip address 209.165.200.1 255.255.255.224 R2(config-if)# ip nat outside R2(config-if)# exit R2(config)# access-list 1 permit 192.168.0.0 0.0.0.31
Which addresses will be translated by NAT?
- 10.1.1.2 to 10.1.1.255
- 192.168.0.0 to 192.168.0.255
- 192.168.0.0 to 192.168.0.31
- 209.165.200.240 to 209.165.200.255
- Only host 10.1.1.2
- Only host 209.165.200.255
Explanation: The access-list determines what IP addresses can be translated. With a wildcard of 0.0.0.31, the first 27 bits have to match. Write 192.168.0.0 in binary and draw a line after the first 27 bits. If you place all 0s after the line, you get the first number translated (192.168.0.0). Then place all 1s to the right of the line and determine that IP address to determine the last number translated (192.168.0.31).
6. Consider the following topology.
On which interface(s) would NAT be applied?
- Only S0/1/0
- Only Gi0/0
- Only on S0/1/0 and Gi0/0
- Only on Gi0/0 and Gi0/1
- Only on S0/1/0, Gi0/0, and Gi0/1
- On all interfaces
Explanation: R1 is the connection to the Internet, so R1 should have NAT configured. The external interface is S0/1/0. The internal interface is Gi0/0.
7. Which NAT solution allows external users to access an internal SFTP server on a network that uses private IP addresses?
- Dynamic NAT
- PAT
- Static NAT
- NAT overload
Explanation: Servers need addresses that do not change; therefore, a static NAT is needed.
8. What are two disadvantages of NAT? (Choose two.)
- Uses too many legally registered addresses.
- Decreases the number of connections that can be used to the public network.
- Network device performance.
- End-to-end traceability is lost.
- Increased network costs.
- Increased provider costs.
Explanation: The device doing the NAT must track network conversations. If there are quite a few network conversations occurring, the device doing the translations might have performance issues. Disadvantages of NAT include the following.
- Hosts on the Internet appear to communicate directly with the NATenabled device instead of the actual host.
- NAT affects time-sensitive packets such as VoIP.
- End-to-end addressing is lost.
- End-to-end traceability is lost.
- Tunneling protocols such as IPsec are negatively affected.
9. What is the last step in configuring PAT with an address pool?
- Creating the access list
- Defining the address pool
- Binding the access list to the address pool
- Applying NAT to at least two interfaces
Explanation: Applying NAT to an interface before the other configuration parameters have been created will cause a loss of connectivity.
10. What parameter defines what internal addresses are translated by NAT?
- The access list
- The address pool
- The interface(s) that have the command ip nat inside applied
- The interface(s) that have the command ip nat outside applied
Explanation: The access list determines that addresses must be “matched” in order to be translated using NAT.
11. What is the effect of adding the keyword overload to a NAT configuration?
- More interfaces can participate in NAT.
- More internal address can be translated into one or more public addresses.
- The router is placed into stealth mode verifying that the address translation is not overtaxing the router hardware.
- Public IP addresses can be added to the NAT pool dynamically.
Explanation: The overload keyword is used in PAT configurations. PAT can use the IP address of the external interface for all translations or can use an address pool of addresses that is fewer in number than the actual number of private, internal addresses that need translation.
12. What is the most commonly deployed IPv6 NAT method recommended for all IPv6-based companies?
- NAT for IPv6
- IPv6 tunneling
- PAT for IPv6
- None of these
Explanation: IPv6 should be run natively whenever possible. At times during IPv4 to IPv6 conversion, a company must either run both protocols, use tunneling for IPv6, or use NAT64.