Cisco CCNA NAT for IPv4 Questions and Answers — Questions and Answers
Question 1: A network administrator configures a Cisco router to translate multiple private IP addresses from the 192.168.10.0/24 network to a single public IP address on its GigabitEthernet0/0 interface. Which command correctly configures this Port Address Translation (PAT)?
- ip nat inside source list 1 interface GigabitEthernet0/0 overload (Correct answer)
- ip nat inside source static 192.168.10.10 203.0.113.5
- ip nat inside source list 1 pool MY_POOL
- ip nat pool MY_POOL 203.0.113.5 203.0.113.5 netmask 255.255.255.0
Correct answer: ip nat inside source list 1 interface GigabitEthernet0/0 overload
To configure PAT, also known as NAT Overload, the 'overload' keyword is essential. This keyword allows many internal (inside local) addresses to be translated to a single public (inside global) address by tracking unique port numbers for each session. The command `ip nat inside source list 1 interface GigabitEthernet0/0 overload` correctly ties an access list (list 1) to the public interface's IP address and enables the overload functionality.
Question 2: In the context of NAT terminology, what does the 'inside global' address represent?
- The IP address of an internal host as it appears to the public network. (Correct answer)
- The private IP address assigned to a host on the internal network.
- The public IP address of a destination host on the internet.
- The IP address of an external host as it appears to the internal network.
Correct answer: The IP address of an internal host as it appears to the public network.
The 'inside global' address is the public, routable IP address that represents one or more 'inside local' addresses to the outside world. When a packet from an internal host traverses a NAT router, its source address (the inside local) is translated to the inside global address.
Question 3: A company has a web server with the private IP address 10.1.1.100. The network administrator needs to make this server permanently accessible from the internet via the public IP address 209.165.200.225. Which type of NAT should be configured to achieve this one-to-one mapping?
- Dynamic NAT
- PAT (NAT Overload)
- Static NAT (Correct answer)
- Policy-Based NAT
Correct answer: Static NAT
Static NAT creates a persistent, one-to-one mapping between a private (local) IP address and a public (global) IP address. This is ideal for making internal resources like web servers consistently reachable from the outside network.
Question 4: A network technician is troubleshooting an issue where internal users cannot access the internet. On the edge router, the command `show ip nat statistics` reveals a large number of 'misses' but zero 'hits'. The configuration is intended to use a pool of public IP addresses for translation. What is the most likely cause of this issue?
- The NAT pool is completely exhausted of available addresses.
- The access list defining traffic to be translated is not matching any packets. (Correct answer)
- The `ip nat outside` command is configured on the wrong interface.
- The `ip nat inside` and `ip nat outside` interface commands are missing.
Correct answer: The access list defining traffic to be translated is not matching any packets.
In NAT statistics, 'hits' represent successful translations, while 'misses' indicate that a packet required translation but no suitable rule or entry was found. If there are many misses and no hits, it strongly suggests that the traffic from internal users is not being matched by the ACL that defines which traffic should be translated. Therefore, the router never attempts to use the NAT pool for these packets.
Question 5: Which of the following is a primary advantage of using dynamic NAT without overload (PAT) instead of static NAT?
- It allows a specific internal server to be reached from the internet on a fixed public IP.
- It allows multiple internal hosts to share a single public IP address simultaneously.
- It conserves public IP addresses by creating translations only when they are needed for outbound connections. (Correct answer)
- It provides a permanent one-to-one mapping for every host on the internal network.
Correct answer: It conserves public IP addresses by creating translations only when they are needed for outbound connections.
Dynamic NAT allocates a public IP address from a pool to an internal host, but only when that host initiates an outbound connection. The mapping is temporary and is returned to the pool after a period of inactivity. This is more efficient than static NAT, which permanently reserves a public IP for each internal host, whether it's active or not.
Question 6: A PC with the IP address 192.168.50.5 sends a packet to a public web server at 203.0.113.10. The packet traverses a router performing PAT. The router translates the source IP to 209.165.201.30. In this scenario, what does the address 203.0.113.10 represent?
- Inside Local
- Inside Global
- Outside Local
- Outside Global (Correct answer)
Correct answer: Outside Global
The address 203.0.113.10 is the IP address of the destination device located on the external, public network. In NAT terminology, this is known as the 'outside global' address. It is the real, globally routable address of the external host.
Cisco CCNA NAT for IPv4 Questions and Answers
A network administrator configures a Cisco router to translate multiple private IP addresses from the 192.168.10.0/24 network to a single public IP address on its GigabitEthernet0/0 interface.
Which command correctly configures this Port Address Translation (PAT)?