final exam review knowledge questions true or false statement (explain why) protocol calculation...
TRANSCRIPT
Final Exam Review• Knowledge questions
• True or false statement (explain why)
• Protocol
• Calculation
• Cover the contents after midterm coverage
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?
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)
Protocol Problem Examples
• NAT address translation procedure
• Digital signature procedure
• HTTPS connection procedure– CA, public key
• Secure email (assume known public key)– Confidentiality– Integrity
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)
• 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
Intra-AS and Inter-AS routing
Host h2
a
b
b
aaC
A
Bd c
A.a
A.c
C.bB.a
cb
Hosth1
Intra-AS routingwithin AS A
Inter-AS routingbetween A and B
Intra-AS routingwithin AS B
• We’ll examine specific inter-AS and intra-AS Internet routing protocols shortly
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
NAT: Network Address Translation
10.0.0.1
10.0.0.2
10.0.0.3
S: 10.0.0.1, 3345D: 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 tableWAN 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, 5001D: 128.119.40.186, 80
2
2: NAT routerchanges datagramsource addr from10.0.0.1, 3345 to138.76.29.7, 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 routerchanges datagramdest addr from138.76.29.7, 5001 to 10.0.0.1, 3345
Intra-AS and Inter-AS routing
Host h2
a
b
b
aaC
A
Bd c
A.a
A.c
C.bB.a
cb
Hosth1
Intra-AS routingwithin AS A
Inter-AS routingbetween A and B
Intra-AS routingwithin AS B
– RIP: Routing Information Protocol
– OSPF: Open Shortest Path First– BGP: Border Gateway Protocol (Inter-AS)
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
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
Collision Avoidance: RTS-CTS exchange
APA B
time
RTS(A)RTS(B)
RTS(A)
CTS(A) CTS(A)
DATA (A)
ACK(A) ACK(A)
reservation collision
defer
Textbook Page 522 figure
DIFS
CIFS
CIFS
CIFS
Firewall
• Block outside-initiated traffic to inside of a local network
• Usually do not block any traffic initiated from inside to outside
administerednetwork
publicInternet
firewall
large message
mH: Hashfunction H(m)
digitalsignature(encrypt)
Bob’s private
key K B-
+
Bob sends digitally signed message:
Alice verifies signature and integrity of digitally signed message:
KB(H(m))-
encrypted msg digest
KB(H(m))-
encrypted msg digest
large message
m
H: Hashfunction
H(m)
digitalsignature(decrypt)
H(m)
Bob’s public
key K B+
equal ?
Digital signature = signed message digest
No confidentiality !No confidentiality !
Secure e-mail
Alice: generates random symmetric private key, KS. encrypts message with KS (for efficiency) also encrypts KS with Bob’s public key. sends both KS(m) and KB(KS) to Bob.
Alice wants to send confidential e-mail, m, to Bob.
KS( ).
KB( ).+
+
KS(m
)
KB(KS )+
m
KS
KB+
Internet
KS
Secure e-mail
Bob: uses his private key to decrypt and recover KS
uses KS to decrypt KS(m) to recover m
Alice wants to send confidential e-mail, m, to Bob.
KS( ).
KB( ).+
+ -
KS(m
)
KB(KS )+
m
KS
KS
KB+
Internet
KS( ).
KB( ).-
KB-
KS
mKS(m
)
KB(KS )+
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( ). KA( ).-
+ -
H(m )KA(H(m))-
m
KA-
Internet
m
KA( ).+
KA+
KA(H(m))-
mH( ). H(m )
compare
How SSL (https) works?
K B+
ClientServer B
time
Three-way handshake
Request server certificate
K-CA(K+
B)
K+B(KA-B)
KA-B(m)
Symmetric session key
Certificate from CA
Distance table gives routing table
D ()
A
B
C
D
A
3
5
6
4
B
5
4
9
11
D
8
9
4
5
Ecost to destination via
dest
inat
ion
A
B
C
D
A,3
B,4
D,4
A,4
Outgoing link to use, cost
dest
inat
ion
Distance table Routing table
Distance Vector Algorithm: example
X Z12
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
CRC ExampleWant:
D.2r XOR R = nG
equivalently:
D.2r = nG XOR R
equivalently:
if we divide D.2r by G, want remainder R
R = remainder[ ]D.2r
G
Dijkstra’s algorithm: example
Step012345
N D(B),p(B) D(C),p(C) D(D),p(D) D(E),p(E) D(F),p(F)
2
2
13
1
1
2
53
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,EADEB 2,A 3,E 1,A 2,D 4,E
ADEBC 2,A 3,E 1,A 2,D 4,EADEBCF 2,A 3,E 1,A 2,D 4,E
ED
CB
FA