1. You have a host behind a NAT that is exchanging UDP traffic with another host
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Question
1. You have a host behind a NAT that is exchanging UDP traffic with another host outside the NAT. This other host has a publicly routable IP address and is not behind a NAT. The other host has IP address 171.2.1.6 and is using port 9999. Your local UDP port number is 5555, which the NAT has mapped to 7777. There are no other NAT mappings. Your NAT receives a UDP datagram on its external interface. The datagram is from 182.11.5.9, port 7878 to the NAT's IP address, port 5555. Which of the following NAT types will properly forward the datagram to your host? A. Symmetric; B. Full cone; C.Restricted cone; D. Port restricted; E. None of the above 2. (same setup as before) You have a host behind a NAT that is exchanging UDP traffic with another host outside the NAT. This other host has a publicly routable IP address and is not behind a NAT. The other host has IP address 171.2.1.6 and is using port 9999. Your local UDP port number is 5555, which the NAT has mapped to 7777. There are no other NAT mappings. Your NAT receives a UDP datagram on its external interface. The datagram is from 182.11.5.9, port 9999 to the NAT's IP address, port 7777. Which of the following NAT types will properly forward the datagram to your host? A. Symmetric; B. Full cone; C. Restricted cone; D. Port restricted; E. None of the above. 3. (same setup as before) You have a host behind a NAT that is exchanging UDP traffic with another host outside the NAT. This other host has a publicly routable IP address and is not behind a NAT. The other host has IP address 171.2.1.6 and is using port 9999. Your local UDP port number is 5555, which the NAT has mapped to 7777. There are no other NAT mappings. Your NAT receives a UDP datagram on its external interface. The datagram is from 171.2.1.6, port 3535 to the NAT's IP address, port 7777. Which of the following NAT types will properly forward the datagram to your host? A. Symmetric; B. Full cone; C. Restricted cone; D. Port restricted; E. None of the above. (same setup as before) You have a host behind a NAT that is exchanging UDP traffic with another host outside the NAT. This other host has a publicly routable IP address and is not behind a NAT. The other host has IP address 171.2.1.6 and is using port 9999. Your local UDP port number is 5555, which the NAT has mapped to 7777. There are no other NAT mappings. Your host sends a datagram from local port 5555 to 171.55.1.2 port 9999. What NAT types will allocate a new external port for these datagrams? A. Symmetric; B. Full cone; C. Restricted cone; D. Port restricted; E. None of the above.
Explanation / Answer
Correct option is (e) None of the above. The source IP and port(182.11.5.9:7878 ) is not mapped by NAT . The correct destination(NAT) port is 7777 whereas the source is trying to send datagram to port 5555. So, none of the NATs can help. Correct option is (b) Full Cone. The only requirement for a full cone NAT is that datagram comes in on the correct port and even though the source IP and port (182.11.5.9:9999 ) is not mapped by NAT ,the destination(NAT) port is correct(7777). So, full cone NAT can come in handy in this situation. Correct option is (c) Restricted Cone. The source IP(171.2.1.6) is also the local host ip, thus it is pre-mapped.The requirement for a restricted cone NAT is that datagram comes in on the correct port as well as the source IP (171.2.1.6) is already mapped. Correct option is (a) Symmetric Cone. This is because only symmetric NAT is capable of allocating new ports for datagrams.
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