Exam Review Networking CS 3470 Section 1 Sarah

Exam Review Networking CS 3470, Section 1 Sarah Diesburg

Coverage n Total: 100 points; 1 min / point ¡ ¡ n Based on lectures, assignments, and projects Based on your ability to apply various principles learned in the class Multiple choice, short answer, and problem solving questions

Coverage n Two parts ¡ Chapters 5 -6 (last third of class) n ¡ Roughly 50 pts Cumulative (over first 2/3 of class, exams 1 -2) n Roughly 50 pts

Chapters 5 -6 Review

Transport Layer n Definitions ¡ Transport layer n n ¡ Packet Encapsulation n ¡ What is the primary function? Why is it necessary (say on top of IP)? Layer headers are added or taken away Multiplexing/demultiplexing

Transport Layer n Definitions ¡ TCP socket n ¡ UDP socket n ¡ ¡ ¡ Identified by 4 -tuple (IP src, IP dest, port src, port dest) Identified by 2 -tuple (IP dst, IP port) Pseudoheader Flow control Congestion control

Transport Layer ¡ Segments n ¡ Packets exchanged between TCP peers TCP flags n SYN, ACK, FIN, RST

Transport Layer n Short answer / problem solving ¡ ¡ UDP advantages over TCP advantages over UDP Checksum with 1’s compliment Two-Army problem

DNS n Definitions ¡ ¡ What is DNS? Host aliasing n ¡ ¡ MX records Load balancing n ¡ Multiple names for one server Many IP addresses associated with a hostname Canonical name

DNS n Short answers / problem solving ¡ ¡ Role of a root DNS server Role of a top-level domain (TLD) server Be able to create and identify iterative and recursive DNS queries Role of DHCP and DNS

TCP Control Flow n Definitions ¡ ¡ Sequence number field (often called Sequence. Num) Passive open Active open Maximum Segment Lifetime (TCP)

TCP Control Flow n Short answers / problem solving ¡ ¡ ¡ TCP 3 -way handshake Goals of TCP sliding window Advertised. Window/Effective. Window (see next slide)

Sliding Window Revisited Sender n Receiver Be able to look at a sliding window diagram and show me the Advertised. Window (on receiver) and Effective. Window (on sender)

TCP Transmission Control n Definitions ¡ ¡ ¡ Silly window syndrome Fast retransmit (3 duplicate ACKs) Nagle’s Algorithm n ¡ Generally, what does it do? (No need to memorize algorithm. ) Adaptive Retransmission n Generally, what does it do? (No need to memorize algorithm. )

TCP Transmission Control n Short answer / problem solving ¡ ¡ TCP’s three mechanisms to trigger the transmission of a segment General TCP behavior -- ACK generation (see next slide)

TCP ACK generation [RFC 1122, RFC 2581] Event at Receiver TCP Receiver action Arrival of in-order segment with expected seq #. All data up to expected seq # already ACKed Delayed ACK. Wait up to 500 ms for next segment. If no next segment, send ACK Arrival of in-order segment with expected seq #. One other segment has ACK pending Immediately send single cumulative ACK, ACKing both in-order segments Arrival of out-of-order segment higher-than-expect seq. #. Gap detected Immediately send duplicate ACK, indicating seq. # of next expected byte Arrival of segment that partially or completely fills gap Immediately send ACK, provided that segment starts at lower end of gap

Queuing Disciplines n Definitions ¡ ¡ ¡ Flow FIFO queuing FIFO priority queuing Tail drop Fair queuing

Queuing Disciplines n Short answers / problem solving ¡ ¡ ¡ How do queuing disciplines relate to congestion control? What is Fi in fair queuing? Be prepared to answer queuing problems as seen in homework 9, question 3

TCP Congestion Control n Definitions ¡ ¡ Congestion window (or Cong. Win) TCP loss event n n ¡ ¡ ¡ Why do we care about losses? Timeout or 3 duplicate ACKs Additive Increase/Multiplicative Decrease (AIMD) Slow Start Fast Recovery

TCP Congestion Control n Short answers / problem solving ¡ ¡ ¡ Explain how AIMD and slow start work Explain how fast recovery works Explain how TCP is fair n ¡ Is all traffic fair? Homework 9, questions 1 -2

Summary: TCP Congestion Control � When Cong. Win is below Threshold, sender in slow-start phase, window grows exponentially. � When Cong. Win is above Threshold, sender is in congestion-avoidance phase, window grows linearly. � When a triple duplicate ACK occurs, Threshold set to Cong. Win/2 and Cong. Win set to Threshold. � When timeout occurs, Threshold set to Cong. Win/2 and Cong. Win is set to 1 MSS.

TCP sender congestion control Event State TCP Sender Action Commentary ACK receipt Slow Start for previously (SS) unacked data Cong. Win = Cong. Win + MSS, If (Cong. Win > Threshold) set state to “Congestion Avoidance” Resulting in a doubling of Cong. Win every RTT ACK receipt Congestion for previously Avoidance unacked data (CA) Cong. Win = Cong. Win+MSS * (MSS/Cong. Win) Additive increase, resulting in increase of Cong. Win by 1 MSS every RTT Loss event detected by triple duplicate ACK SS or CA Threshold = Cong. Win/2, Cong. Win = Threshold, Set state to “Congestion Avoidance” Fast recovery, implementing multiplicative decrease. Cong. Win will not drop below 1 MSS. Timeout SS or CA Threshold = Cong. Win/2, Cong. Win = 1 MSS, Set state to “Slow Start” Enter slow start Duplicate ACK SS or CA Increment duplicate ACK count for segment being acked Cong. Win and Threshold not changed

Congestion Avoidance n Definitions ¡ ¡ DECbit RED gateways

Network Programming n n Look over your projects and be able to tell me the differences between setting up a TCP connection and a UDP connection What does a pipe (“|”) and redirection (“>” or “<“) do?

Putting it all together Review

Putting it all together n Wireshark ¡ ¡ I may paste a screenshot of a Wireshark trace and ask you a few questions about it Review project 4 to prepare

Putting it all together n Definitions ¡ Review definitions and general concepts from previous reviews and old tests

Putting it all together n The following problem-solving questions may show up on the final: ¡ ¡ ¡ Calculate the total time required to transfer a file (recall the definition of latency) SMTP protocol Drawing windows in the sliding window protocol

Putting it all together ¡ ¡ ¡ ISO/OSI vs Internet Model Determining next hop for a CIDR network Dijkstra's algorithm TCP simple talk control flow Host vs network order