1. Midterm Review These slides contain 90% recycled content.

2. Problem 1: Network Address Translation Src: 192.168.4.56:2410 Dst: 4.3.2.1:80 Src: 128.32.131.210:80 Dst: 74.125.224.50:2500 Could the packet leaving A have the wrong source address? Wrong destination address? ?

3. Problem 1: Network Address Translation NAT 2 192.168.4.56:2410 4.3.2.1 74.125.224.50 128.32.131.210:80 Src: 192.168.4.56:2410 Dst: 4.3.2.1:80 Src: 128.32.131.210:80 Dst: 74.125.224.50:2500 NAT 1 Packet leaving A Packet leaving B Packet leaving NAT 1? Packet leaving NAT 2? Packet leaving APacket leaving B

4. Problem 3: Learning Switch P1 P2 P3 P4 5 E→A D→A C→A A→B B→E E→B D→A C→B E B AE C D

5. AF E D B C 3 1 3 1 4 7 3 5 1 Problem 4ii: Routing [option 1] AF E D B C 3 1 3 1 4 7 3 5 1

6. Problem 4ii: Routing [option 2] AF E D B C 3 1 3 1 4 7 3 5 1 AF E D B C 3 1 3 1 4 7 3 5 1

7. Problem 5: Packet Transmission FTP: 1 bit per 10 seconds – Apartment is 300 meters away RTP: 256GB flash drive, 5 minutes each way

8. Topics Following slides list some points for discussion, taken from lecture slides. Not deliberately mid- term related Haven’t written new questions – Want your questions!

9. 10. IP Addressing and Forwarding Fragmentation IPv4 and IPv6 Header Comparison Security analysis: sender Addressing: Layer 2 vs. 3 – Scalability (State, Churn): aggregation – Hierarchical addressing (network:host) [S6 P1] – Classful – CIDR [S6 P1]

10. IP Header: Security analysis 4-bit Version 4-bit Header Length 8-bit Type of Service (TOS) 16-bit Total Length (Bytes) 16-bit Identification 3-bit Flags 13-bit Fragment Offset 8-bit Time to Live (TTL) 8-bit Protocol 16-bit Header Checksum 32-bit Source IP Address 32-bit Destination IP Address Options (if any) Payload Slide 49, Lecture 9; Slides 19-31, Lecture 10 Evasion Ambiguity Datagram limit State-holding

11. 11. Forwarding Dealing with address scarcity – Dynamic Host Configuration Protocol [S6 P2] – Network Address Translation [S6 P2, S7 P1] Address aggregation [S6 P1] Longest prefix match [S6 P1]

12. 12. Transport and TCP Role of transport layer Sliding window TCP Header Three-Way Handshake Normal Termination, One Side At A Time Abrupt Termination Retransmission Timeout (RTO)

13. Role of transport layer De-multiplexing Corruption Translating between byte-streams and packets Reliability Not overloading receiver Not overloading network “Connection” set-up & tear-down Slide 20, Lecture 12

14. TCP Header Slide 72, Lecture 12 Source portDestination port Sequence number Acknowledgment Advertised window HdrLen Flags 0 ChecksumUrgent pointer Options (variable) Data Flags: SYN ACK FIN RST PSH URG