Network Address Translation

Question 1

What does the Network Address Translation (NAT) do?

Answer 1

Modifying layer 3 and 4 addressing in a packer while it is being forwarded

Question 2

?What is a major use-case for NAT?

Answer 2

Private IPv4 addressing translated to public addressing

Question 3

What device makes the change to the packet?

Answer 3

the forwarding device (like router) in the path makes the change

Question 4

What is Static NAT?

Answer 4

one to one mapping of internal IP address to external IP address

Question 5

True or False: External devices can reach internal devices in a static NAT

Answer 5

true

Question 6

What is a Dynamic NAT?

Answer 6

One to one to many mapping of internal IP address to a pool of external IP addresses

Question 7

True or False: In a Dynamic NAT external devices cannot reach internal devices

Answer 7

True

Question 8

What is Port Address Translation (PAT) / NAT overload?

Answer 8

Many to one mapping of internal IP addresses to a single external IP address

Question 9

Static NAT:

Answer 9

One-to-one: one internal IP to one specific external IP

Question 10

Dynamic NAT:

Answer 10

one-to-one-of-many: one internal IP to an external IP in a range

Question 11

PAT/NAT Overloading

Answer 11

Many-to-one: many internal IP addresses to one external IP

Question 12

True or False: PAT/NAT overloading does not require an IP address and a port

Answer 12

False

Question 13

What are the four main concerns about NAT?

Answer 13

Performance, Fragmentation, End-to-end connectivity/principle, and IP address in application data

Question 14

Why is performance a concern for NAT? (2 reasons)

Answer 14

1) Modifying the IP header by changing the IP address requires NAT device to recalculate the IP header checksum
2) Modifying the port number requires NAT device to recalculate the TCP checksum

Question 15

Why is fragmentation a concern for NAT? (one reason)

Answer 15

care has to be taken so that a datagram that is fragmented before reaching the NAT device is not assigned different IP address or port numbers for each fragmentation

Question 16

Why is end-to-end connectivity/principle a concern for NAT? (three reasons)

Answer 16

1) NAT destroys universal end-to-end reachability of hosts on the internet
2) a host in public internet often cannot initiate communication to host in private network
3) serious problem when two hosts that are in different private networks need to communicate with each other