Midterm Review

These slides contain 90% recycled content.

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?

?

Problem 1: Network Address Translation

NAT 2

192.168.4.56:2410

4.3.2.174.125.224.50

128.32.131.210:80

Src: 192.168.4.56:2410

Dst: 4.3.2.1:80Src: 128.32.131.210:80

Dst: 74.125.224.50:2500

NAT 1Packet

leaving A

Packet leaving B

Packet leaving NAT 1?

Packet leaving NAT 2?

Packet leaving A Packet leaving B

Problem 3: Learning Switch

P1

P2

P3

P4

5

E→A

D→A

C→A

A→B

B→E

E→B

D→A

C→BEB

AE

C

D

A F

E

D

B

C

3

1 3

1

4

7

35

1

Problem 4ii: Routing [option 1]

A F

E

D

B

C

3

1 3

1

4

7

35

1

Problem 4ii: Routing [option 2]

A F

E

D

B

C

3

1 3

1

4

7

35

1

A F

E

D

B

C

3

1 3

1

4

7

35

1

Problem 5: Packet Transmission

• FTP: 1 bit per 10 seconds– Apartment is 300 meters away

• RTP: 256GB flash drive, 5 minutes each way

THIS QUESTION IS GOING TO BE

– WAIT FOR IT –

END-TO-END DELAYS

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!

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]

IP Header: Security analysis4-bit

Version

4-bitHeaderLength

8-bitType of Service

(TOS)16-bit Total Length (Bytes)

16-bit Identification3-bitFlags 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

EvasionAmbiguityDatagram limitState-holding

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. 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)

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

TCP Header

Slide 72, Lecture 12

Source port Destination port

Sequence number

Acknowledgment

Advertised windowHdrLen Flags0

Checksum Urgent pointer

Options (variable)

Data

Flags: SYNACKFINRSTPSHURG