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1. A device D1 with an IP address of 192.18.1.1 and a MAC address of 2F-1A-04-37

ID: 3826350 • Letter: 1

Question

1. A device D1 with an IP address of 192.18.1.1 and a MAC address of 2F-1A-04-37-12-E2 is located in a LAN (LAN 1)that is connected to the internet through a router with an interface IP address of 192.18.1.12 and a MAC address of 02-13-56-1A-2B-3C. This router supports another LAN (LAN 2)through an interface with an IP address of 10.120.12.18 and a MAC address of 14-24-35-46-61-0C. A device D2 residing in LAN 2 has an IP address of 10.120.12.34 with a MAC address of 3A-85-63-24-B2-11. If device D1 is sending a message to device D2, determine the source and destination addresses at the IP layer and the data link layer of the datagrams from D1 to D2. (20 pts.)

Explanation / Answer

1) The question is related to NATTING concept in networking.

2)All the IP addresses provided in the question are Private IP's.

IP packet of D1 :

Source IP - 192.18.1.1

Dest IP - 10.120.12.34

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IP packet of Router Intf 1 :

Source IP - 192.18.1.12

Dest IP - 10.120.12.34

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3) In natting Routers maintain the private and public ip tables.

4) if request is made by D2 to D1 , during the transfer through router it record its Ip and the destination it wants to send for.

5) when D1 responds back , Router by seeing previous entries in NAT table tranfers the packet to d2