L29. Describe the role and functioning of NAT

Question 1

What is NAT?

Answer 1

Network address translation (NAT) is a method of mapping an IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device.

Question 2

Why is NAT needed?

Answer 2

For conserving global address space in the face of IPv4 address exhaustion.

Question 3

What does NAT do?

Answer 3

It allows multiple devices on a local network to access external networks, particularly the Internet, using one or a few public IP addresses. Without NAT, every device on the internet would need a unique public IP address. By translating private IP addresses to a public IP address, NAT conserves the number of public IP addresses required, mitigating the issue of IPv4 address exhaustion.

Question 4

How does NAT improve security?

Answer 4

NAT acts as a barrier between the internal network and the external network. It hides the internal IP addresses from the outside world, making it harder for attackers to directly target individual devices within the private network.

Question 5

How does NAT simplify network management?

Answer 5

By enabling internal IP address changes without affecting the external communication

Question 6

How does NAT work?

Answer 6

NAT operates by modifying network address information in the IP header of packets as they pass through a router or firewall.

When a device inside the private network initiates a connection to an external network, the NAT device modifies the source IP address in the packet header to the public IP address assigned by the ISP. It also assigns a unique port number to the connection. The modified packet is then sent to the external network.

When a response packet is received from the external network, the NAT device looks up the translation table to find the corresponding private IP address and port number. It then modifies the destination IP address and port number in the packet header to match the original private IP address and port number. The packet is then forwarded to the appropriate device within the private network.

Question 7

What are the three most common types of NAT?

Answer 7

1. Static NAT, which maps a single private IP address to a single public IP address.
2. Dynamic NAT, which maps a private IP address to a public IP address from a pool of public IP addresses.
3. Port Address Translation (PAT), also known as Overloading or NAT overload, which allows multiple devices on a local network to be mapped to a single public IP address but with a different port number for each session.

Question 8

What is static NAT and what is it used for?

Answer 8

A type of NAT that maps a single private IP address to a single public IP address. This one-to-one translation is often used for hosting services that need to be accessible from the internet, such as web servers.

Question 9

What is dynamic NAT and what is it used for?

Answer 9

A type of NAT that maps a private IP address to a public IP address from a pool of public IP addresses. The mapping can change dynamically, providing flexibility in address allocation.

The main purpose of dynamic NAT is to allow multiple devices within a private network to access resources on the internet simultaneously using a single or a pool of public IP addresses.

Question 10

What is PAT and what is it used for?

Answer 10

Port Address Translation (PAT), also known as Overloading or NAT overload, is a type of NAT that allows multiple devices on a local network to be mapped to a single public IP address but with a different port number for each session. This is the most common type of NAT used in home routers.

Question 11

How does NAT translate addresses?

Answer 11

The NAT device keeps a translation table that records the mapping between the private IP address and port number to the public IP address and port number.

When a response packet is received from the external network, the NAT device looks up the translation table to find the corresponding private IP address and port number.

Question 12

What are the three main benefits of NAT?

Answer 12

1. Efficient use of IP addresses, supporting many devices with a limited number of public IP addresses.
2. Adds a layer of security against external threats by hiding internal IP addresses
3. Allows internal network changes without affecting external connectivity

Question 13

What are three downsides of NAT?

Answer 13

1. Can complicate network troubleshooting because it changes the original IP addresses and port numbers.
2. May cause issues with some protocols that embed IP address information in the payload (like FTP)
3. Adds processing overhead on the router or firewall, which can impact performance, especially in large-scale networks.

Question 14

Why is NAT not needed in IPv6?

Answer 14

IPv6 provides an address space of 128 bits, compared to the 32-bit address space of IPv4. This results in massive numbers of unique IP addresses, eliminating the primary reason for NAT in IPv4, which is address conservation. With IPv6, every device can have its own unique public IP address.

Question 15

How can NAT be used in IPv6?

Answer 15

NAT in IPv6 will evolve to address different needs than address conservation, such as network prefix translation for ISP independence and security measures for topology hiding.

Question 16

What is NPTv6?

Answer 16

Network Prefix Translation (NPTv6), also known as NAT66, translates one IPv6 prefix to another.

Question 17

When is NPTv6 useful?

Answer 17

If an organization changes its Internet Service Provider (ISP) and the global prefix changes, NPTv6 can map the old prefix to the new one, avoiding the need to reconfigure all internal devices.

Although IPv6 includes features like IPsec for security, some organizations may still use NAT for topology hiding. By translating internal addresses to different external addresses, NAT can obscure the internal network structure, providing a layer of security through obscurity.