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Chapters: All Final Review

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Title: Chapters: All Final Review


1
Chapters AllFinal Review
  • Professor Rick Han
  • University of Colorado at Boulder
  • rhan_at_cs.colorado.edu

2
Announcements
  • HW 5 solutions posted on May 4
  • Final May 7, 430-7 pm
  • Tuesdays lecture now on Web
  • Office Hours Monday 3-5 pm
  • Next, final review

3
Format of Final
  • 2 ½ hours
  • Comprehensive
  • In class
  • Closed book
  • Calculator OK
  • About 5-6 multi-part questions
  • About 20-25 minutes for each multi-part question

4
Format of Final (2)
  • Breakdown
  • 4 questions on topics since last midterm (all
    lectures from Feb. 28 onward)
  • 1 each on security, application layer protocols,
    TCP, and IP (including BGP and multicast)
  • 2 questions on topics before the midterm
  • 2 on MAC/link layer and IP

5
Potential Topics for Final
  • List is not all-inclusive some topics may appear
    on final not listed here
  • How does ___ work? Why is it used?
  • Sections in textbook relevant to final
  • Chapter 1 1.1-1.3
  • Chapter 2 2.1-2.8
  • Chapter 3 3.1-3.2
  • Chapter 4 4.1-4.4
  • Chapter 5 5.1-5.2
  • Chapter 6 6.2-6.4
  • Chapter 7 none
  • Chapter 8 8.1-8.4
  • Chapter 9 9.1-9.2

6
Potential Topics for Final (2)
  • All topics in lecture notes are relevant to final
  • Relevant topics in lecture notes but not in the
    textbook
  • SACK TCP
  • TCP extensions window scale time stamp
  • Wireless TCP snoop
  • Web caching proxies
  • Load balancing via DNS, HTTP Redirect,
  • NATs for address translation, firewalling, load
    balancing
  • SMB/Samba
  • Stream ciphers and WEP

7
Potential Topics for Final (3)
  • All topics listed in the Midterm Review, plus the
    following
  • IP
  • Addressing, Subnets, and CIDR
  • BGP
  • IP multicast
  • Link-state multicast
  • DVMRP
  • PIM
  • UDP
  • Unreliable datagram delivery
  • Header, Checksum
  • Multiplexing/demultiplexing

8
Potential Topics for Final (4)
  • TCP
  • Reliable Stream Delivery
  • Header, Checksum
  • Connection setup
  • How does a 3-way handshake work and why does it
    work?
  • SYN, SYN/ACK
  • How does FIN and FIN/ACK exchange differ from SYN
    and SYN/ACK exchange? (half-closed)
  • State machine
  • What states are traversed during connection
    setup?
  • In a normal termination, how does TIME_WAIT state
    differ from CLOSE_WAIT?

9
Potential Topics for Final (5)
  • TCP
  • Sliding window
  • Sequence s and segments
  • Window-based flow control
  • Cumulative ACKs
  • Receiver window advertisements
  • Sender-side vs. receiver-side sliding window flow
    control
  • What is TCP Persist and why is it useful?
  • TCP Extensions
  • Timestamp address wrap-around with seq. s
  • Window scaling keeps pipe full over LFNs

10
Potential Topics for Final (6)
  • TCP
  • Adaptive Retransmission
  • Under what conditions does TCP retransmit?
  • Timeout
  • 3 duplicate ACKs
  • How is the RTT originally estimated?
  • New RTT estimate a (old RTT estimate) (1 - a)
    (new RTT)
  • How is the timeout originally computed from RTT?
  • RTO b RTT, where b 2
  • What were Karn/Partridges refinements to
    original approach?
  • Recompute RTT only for unambiguous ACKs
  • Backoff the timeout exponentially

11
Potential Topics for Final (7)
  • TCP
  • Adaptive Retransmission
  • What were Jacobsen/Karels refinements to timeout
    algorithm?
  • Make the timeout a function of both the average
    and deviation but why?
  • RTO Smoothed Ave 4 Smoothed Dev

12
Potential Topics for Final (8)
  • TCP
  • Congestion Control
  • W min (CW, FW) why?
  • send no more packets than the network can handle
    without loss
  • Sawtooth behavior of CW whats the basic
    principle?
  • Probe network by expanding CW until loss, then
    reduce CW, then grow CW again, etc.
  • Slow Start is actually exponential increase
  • How does a sender detect that CW is too large?
  • A timeout occurs

13
Potential Topics for Final (9)
  • TCP
  • Congestion Control
  • Additive Increase/Multiplicative Decrease
  • After a timeout, divide CW by 2 and store in
    ssthresh
  • Slow start up to ssthresh, then add a/CW if CW
    packets in a RTT are safely ACKed
  • If 3 duplicate ACKs are received, then infer that
    one segment has been lost
  • Retransmit immediately, rather than wait for a
    timeout called Fast Retransmit
  • Cancel slow start, and drop CW to half its value
    (approximately) rather than to one called Fast
    Recovery

14
Potential Topics for Final (10)
  • TCP
  • Congestion Avoidance
  • Back off before there are packet losses
  • Informed by increasing RTT Source-based
  • Informed by routers of congestion DECbit
    (explicit), RED (implicit by dropped packets)
  • Queueing Disciplines
  • What is a drop-tail policy?
  • How do Fair Queueing and Weighted Fair Queueing
    enforce fairness? How are they work-conserving?

15
Potential Topics for Final (11)
  • SACK-TCP
  • Why is this an improvement over vanilla TCP?
  • How are selective ACKs achieved?
  • Wireless TCP
  • What is the major problem with TCP over wireless?
  • Solutions
  • End-to-End approaches ECN, ELN
  • Split connection
  • Link-Layer
  • Snoop TCP is a hybrid TCP-aware
  • Retransmit locally and suppress duplicate ACKs
    all without having to terminate TCP connection
  • Advantages and disadvantages?

16
Potential Topics for Final (12)
  • Application Layer
  • DNS
  • Hierarchical naming
  • Hierarchical resolution of names local, root
    authoritative name servers with
    iterative/recursive resolution
  • Load distribution DNS round robin
  • HTTP
  • Stateless Request/Response protocol using text
  • Persistent HTTP 1.1
  • HTTP Caching Proxies relevant headers?
  • HTTP Redirect for load balancing
  • SMTP, MIME, and how is email relayed via SMTP
    mail gateways?

17
Potential Topics for Final (13)
  • Network Address Translation (NAT)
  • How does it work?
  • Replace senders IP addr and source TCP port with
    NATs IP addr and source TCP port
  • Dynamic NAT serves as firewall
  • Static NAT allows inbound traffic on designated
    ports
  • Load balancing via NAT
  • IPSec and NATs whats the conflict?
  • TCP ports are encrypted
  • Even if TCP ports were visible, cant modify
    packet without causing tampering to be detected
    via digital signature

18
Potential Topics for Final (14)
  • SMB/Samba
  • Protocol for mapping file systems between UNIX
    and Windows how does it work?
  • What is NETBIOS and how does it relate to SMB?
  • Security
  • What are the six major characteristics of concern
    in security?
  • Confidentiality, Integrity, Authentication,
    Non-Repudiation, Availability, Authorization
  • What are different types of cryptanalysis
    attacks?
  • Brute force, ciphertext-only, known-plaintext,
    chosen-plaintext, adaptive chosen-plaintext

19
Potential Topics for Final (15)
  • Security
  • Symmetric Key Cryptography
  • Same secret key on both endpoints
  • DES uses 16 stages each employs principles of
    confusion and diffusion
  • What is a block cipher, how is it vulnerable, and
    how does Cipher-Block-Chaining (CBC) address
    this?
  • How do stream ciphers work?
  • What are various ways to securely distribute a
    shared secret key to both endpoints?
  • Diffie-Helman Key Exchange
  • Public key encryption of shared symmetric key
  • Key Distribution Center (KDC) Kerberos

20
Potential Topics for Final (16)
  • Security
  • Public Key Cryptography
  • Asymmetric keys a public key and a private key
  • Helps provide Confidentiality, Authentication,
    Integrity
  • Based on the difficulty of inverting one-way
    functions
  • How does RSA work? (see example)

21
Potential Topics for Final (17)
  • Security
  • Authentication via
  • public-key digital signatures
  • 3-way handshakes
  • Trusted 3rd party
  • Public keys (Fig. 8.11)
  • How do one-way hashes provide data integrity?
  • What are some counterexamples?
  • Checksums for IP and WEP

22
Potential Topics for Final (18)
  • Security
  • Secure distribution of public keys
  • Trusted 3rd party Certificate Authorities (CA)
  • What is a digital certificate and how does it
    certify the provider of the certificate?
  • SSL/TLS how is the secure connection
    established?
  • IPSec
  • End-to-end encryption at the network layer
  • Impact on NATs
  • How do the two protocols AH and ESP provide
    confidentiality, integrity, and/or
    authentication?
  • How is a VPN created using IPSec?

23
Potential Topics for Final (19)
  • Security
  • Firewalls
  • Packet filters
  • Proxies
  • What are some sample policies that firewalls
    could implement? How are they flawed?
  • Good luck on the Final!
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