Friday, February 5, 2016

Consider a firewall that protects the network

10:26 PM

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Consider a firewall that protects the network shown in the figure below. 2.1 Explain the meaning of each field of the following packet filtering rule. (13 points) Firewall rule Packet direction Source address Dest address Packet type Source port Dest port ACK action C Incoming ext 132.28.6.4 TCP 23 * * deny 2.2 If a packet is permitted by the following packet filtering rule, that is, the packet matches the rule: Firewall rule Packet direction Source address Dest address Packet type Source port Dest port ACK action D Outgoing int ext TCP * 23 * permit 4. 2.2.1: Who is the sender program (of the packet) and where is the sender (inside the firewall or outside the firewall)? (7 points) 5. 2.2.2: Who is the receiver program (of the packet) and where is the receiver (inside the firewall or outside the firewall)? (7 points) 6. 2.2.3: What are the IP address and port number of the receiver program? (7 points) 7. 2.2.4: Could computer 168.3.144.1 be the machine on which the receiver program is running? Why? (8 points 2.2.5: Could this packet be the second sub-step packet (or signal) of the 3-way handshake process of the TCP session (or connection)? Why? (8 points) 9. 2.2.6: Could this packet be the third sub-step packet (or signal) of the 3-way handshake process of the TCP session (or connection)? Why? (8 points) 2.2.7: After the receiver program receives this packet, if the receiver wants to send a packet back to the sender, the above rule (rule D) does not authorize this packet to go through the firewall. 10. 2.2.7.1: Why rule D does not authorize this packet to go through the firewall? (8 points) 11. 2.2.7.2: A TCP connection has 3 steps (or phases): establish the connection, messages back and forth, terminate the connection. Is this packet part of Step 1, Step 2, or Step 3? (8 points) 12. 2.2.7.3: Give a rule which authorizes this new packet to go through the firewall. (8 points) 13.

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