1. Final Exam Review Knowledge questions True or false statement (explain why) Protocol Calculation Cover the contents after midterm coverage

2. Knowledge Question Examples Three classes of switch fabric, speed relationship –What is Head-of-the-line (HOL) blocking? Where can queue occur in router? TCP header size? IP header size? UDP header size? How many bits in IP of IPv6? Address space size? Why it is very slow to be deployed? (enough IP space, hard upgrading and compatible) Routing: what are Link state, distance vector? Internet two-level routing? (inter-AS, intra-AS) RIP, OSPF, BGP? Used where? –OSPF uses link state, BGP/RIP uses distance vector Which is better? pure ALOHA, slotted ALOHA, CSMA/CD? –What are their assumptions? (collision detection, time syn) CSMA/CD? CSMA/CA? Why wireless use CSMA/CA?

3. Knowledge Question Examples Ethernet Broadcast MAC addr.? What the broadcast address for? What is ARP? Why Ethernet is much better than aloha in efficiency? (homework 3) Hub vs. Switch? (homework 3) 802.11a, b, g: speed? Working frequency? 802.15? (personal area network, example: bluetooth) Wireless no collision detection? –listen while sending, fading, hidden terminal Network security three elements: –Confidentiality, authentication, integrity What is public/symmetric key cryptography? Pro vs. con? Why use “nonce” in security? (replay attack) What is man-in-the-middle attack? Usage of firewall? (block outside active traffic to inside) IP spoofing? SYN flood DoS attack? UDP flood? What is a botnet? Different between email virus vs. worm? –Vulnerability, user interaction to propagate, speed IPSec vs. SSL? (different layers, tcp vs. udp)

4. Protocol Problem Examples NAT address translation procedure Digital signature procedure HTTPS connection procedure –CA, public key Secure email (assume known public key) –Confidentiality –Integrity

5. Calculation Examples Homework 3 prob. 7 (subnet addressing) Homework 2, prob. 9-11 (link state, distance vector) Homework 3, prob. 4 (parity checking) Homework 3, prob. 5 (CRC calculation) Homework 3, prob. 11 (wireless MAC protocol) Caesar cipher decrypt, Vigenere cipher, one-time pad decrypt (given the pad)

6. Three types of switching fabrics Property? Speed order?

7. Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward Queue can occur at both input port and output port of a router

8. Intra-AS and Inter-AS routing Host h2 a b b a a C A B d c A.a A.c C.b B.a c b Host h1 Intra-AS routing within AS A Inter-AS routing between A and B Intra-AS routing within AS B We ’ ll examine specific inter-AS and intra- AS Internet routing protocols shortly

9. Routing Algorithm classification Global or decentralized information? Global: all routers have complete topology, link cost info “ link state ” algorithms Decentralized: router knows physically-connected neighbors, link costs to neighbors iterative process of computation, exchange of info with neighbors “ distance vector ” algorithms

10. NAT: Network Address Translation 10.0.0.1 10.0.0.2 10.0.0.3 S: 10.0.0.1, 3345 D: 128.119.40.186, 80 1 10.0.0.4 138.76.29.7 1: host 10.0.0.1 sends datagram to 128.119.40.186, 80 NAT translation table WAN side addr LAN side addr 138.76.29.7, 5001 10.0.0.1, 3345 …… S: 128.119.40.186, 80 D: 10.0.0.1, 3345 4 S: 138.76.29.7, 5001 D: 128.119.40.186, 80 2 2: NAT router changes datagram source addr from 10.0.0.1, 3345 to 138.76.29.7, 5001, updates table S: 128.119.40.186, 80 D: 138.76.29.7, 5001 3 3: Reply arrives dest. address: 138.76.29.7, 5001 4: NAT router changes datagram dest addr from 138.76.29.7, 5001 to 10.0.0.1, 3345

11. Intra-AS and Inter-AS routing Host h2 a b b a a C A B d c A.a A.c C.b B.a c b Host h1 Intra-AS routing within AS A Inter-AS routing between A and B Intra-AS routing within AS B –RIP: Routing Information Protocol –OSPF: Open Shortest Path First –BGP: Border Gateway Protocol (Inter-AS)

12. ARP protocol: Same LAN (network) A wants to send datagram to B, and B ’ s MAC address not in A ’ s ARP table. A broadcasts ARP query packet, containing B's IP address –Dest MAC address = FF-FF-FF-FF-FF-FF –all machines on LAN receive ARP query B receives ARP packet, replies to A with its (B's) MAC address –frame sent to A ’ s MAC address (unicast) A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) –soft state: information that times out (goes away) unless refreshed ARP is “ plug-and-play ” : –nodes create their ARP tables without intervention from net administrator

13. What is network security? Confidentiality: only sender, intended receiver should “ understand ” message contents –sender encrypts message –receiver decrypts message Authentication: sender, receiver want to confirm identity of each other –Virus email really from your friends? –The website really belongs to the bank? Message Integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection –Digital signature

14. Collision Avoidance: RTS-CTS exchange AP A B time RTS(A) RTS(B) RTS(A) CTS(A) DATA (A) ACK(A) reservation collision defer Textbook Page 522 figure DIFS CIFS

15. Firewall Block outside-initiated traffic to inside of a local network Usually do not block any traffic initiated from inside to outside firewall

16. large message m H: Hash function H(m) digital signature (encrypt) Bob’s private key K B - + Bob sends digitally signed message: Alice verifies signature and integrity of digitally signed message: K B (H(m)) - encrypted msg digest K B (H(m)) - encrypted msg digest large message m H: Hash function H(m) digital signature (decrypt) H(m) Bob’s public key K B + equal ? Digital signature = signed message digest No confidentiality !

17. Secure e-mail Alice:  generates random symmetric private key, K S.  encrypts message with K S (for efficiency)  also encrypts K S with Bob’s public key.  sends both K S (m) and K B (K S ) to Bob.  Alice wants to send confidential e-mail, m, to Bob. K S ( ). K B ( ). + + K S (m ) K B (K S ) + m KSKS KBKB + Internet KSKS

18. Secure e-mail Bob:  uses his private key to decrypt and recover K S  uses K S to decrypt K S (m) to recover m  Alice wants to send confidential e-mail, m, to Bob. K S ( ). K B ( ). + + - K S (m ) K B (K S ) + m KSKS KSKS KBKB + Internet K S ( ). K B ( ). - KBKB - KSKS m K S (m ) K B (K S ) +

19. Secure e-mail (continued) Alice wants to provide message integrity (unchanged, really written by Alice). Alice digitally signs message. sends both message (in the clear) and digital signature. H( ). K A ( ). - + - H(m ) K A (H(m)) - m KAKA - Internet m K A ( ). + KAKA + K A (H(m)) - m H( ). H(m ) compare

20. How SSL (https) works? K B + Client Server B time Three-way handshake Request server certificate K - CA (K + B ) K + B (K A-B ) K A-B (m) Symmetric session key Certificate from CA

21. Distance table gives routing table D () A B C D A3564A3564 B 5 4 9 11 D8945D8945 E cost to destination via destination ABCD ABCD A,3 B,4 D,4 A,4 Outgoing link to use, cost destination Distance table Routing table

22. Distance Vector Algorithm: example X Z 1 2 7 Y D (Y,Z) X c(X,Z) + min {D (Y,w)} w = = 7+1 = 8 Z D (Z,Y) X c(X,Y) + min {D (Z,w)} w = = 2+1 = 3 Y

23. CRC Example Want: D. 2 r XOR R = nG equivalently: D. 2 r = nG XOR R equivalently: if we divide D. 2 r by G, want remainder R R = remainder[ ] D.2rGD.2rG

24. Dijkstra ’ s algorithm: example Step 0 1 2 3 4 5 N D(B),p(B) D(C),p(C) D(D),p(D) D(E),p(E) D(F),p(F) 2 2 1 3 1 1 2 5 3 5 A 2,A 5,A 1,A infinity,- infinity,- AD 2,A 4,D 1,A 2,D infinity,- ADE 2,A 3,E 1,A 2,D 4,E ADEB 2,A 3,E 1,A 2,D 4,E ADEBC 2,A 3,E 1,A 2,D 4,E ADEBCF 2,A 3,E 1,A 2,D 4,E E D CB F A

25. Caesar cipher decrypt: –“welcome”, key= +2  Vigenere cipher –“final exam” key=3,4,-1 (blank space does not change)