This document summarizes topics that may be covered on a CS144 review session exam, including testing simultaneous open connections in TCP, logistics of the exam, sample exam questions and explanations, an overview of protocols like TCP, IP, and DNS, and concepts related to routing, physical layer transmission, and more. Sample exam questions are provided to illustrate the level of detail and reasoning expected in answers.

1. CS144 Review Session 1
Alex Quach

2. Lab 5
● How to test simultaneous open?
○ Use filter functionality (on website) to pretend that myth1 is
outside NAT (set myth1's IP to go to eth1/2).
○ Add test code to your router that changes packets whose
source is myth2 to go to myth1.
○ Then using telnet, nc, or Python TCP sockets (http:
//stackoverflow.com/questions/2231283/tcp-two-sides-trying-to-
connect-simultaneously/8341693#8341693) connect from
myth1:portB to router:portA (unsolicited SYN).
○ Follow it with a connection from myth2:portC to router:portB
(inside SYN).
○ Alternatively, don't send the inside SYN and test port
unreachable timeout.
○ For more detailed instructions, see http://piazza.
com/class#fall2011/cs144/564

3. Logistics
● Open note
● Identical format to midterm, but longer.
● Questions drawn from both halves of the
quarter.
● Explain your reasoning!

4. Sample Question
● Why do we have a TIME_WAIT state in
TCP?

5. Sample Question
● Why do we have a TIME_WAIT state in
TCP?
● "Because TCP connections wouldn't shut
down correctly otherwise."
● Better: "Because the active closer needs
to handle the case where its final ACK
gets lost. Without TIME_WAIT, it would
close and the other side would be stuck
waiting for the ACK forever."

6. Protocols
● Built as layers on top of each other
● What's encapsulation?
● What is the hourglass model?

7. Protocols
● Built as layers on top of each other
● What's encapsulation?
○ Protocols are nested within each other
with minimal cross-protocol
communication. Provides numerous
benefits (lack of tight coupling, clean
structure).
● What is the hourglass model?
○ Many physical protocols below IP, many
application protocols above IP. IP is the
narrow waist.

8. TCP
● What's end-to-end?
● Why do we need to be reliable?
● What is "reliable?"
● What is the 3-way handshake and why do
we need it?

9. TCP
● What's end-to-end?
○ Push all intelligence to ends of network.
● Why do we need to be reliable?
○ Network can drop, reorder, duplicate, corrupt
packets.
● What is "reliable?"
○ We can recover from some network problems and
let the user know if this isn't the case.
● What is the 3-way handshake and why do we need
it?
○ The beginning of every TCP connection. Used to
synchronize information and ensure connection is
open.

10. TCP
● What's the difference between flow
control and congestion control?
● What is additive increase, multiplicative
decrease?
● Make sure you understand the state
diagram!

11. TCP
● What's the difference between flow
control and congestion control?
○ Flow control: managing sender vs.
receiver speeds
○ Congestion control: managing network
congestion
● What is additive increase, multiplicative
decrease?
○ TCP policy for window size.

12. IP
● What's fragmentation?
● Does fragmentation increase probability
that packet makes it to destination?
● What's LPM?
● What's DHCP?

13. IP
● What's fragmentation?
○ Packet broken up into smaller payloads to
support smaller MTU.
● Does fragmentation increase probability that
packet makes it to destination?
○ No! Any one fragment dropped means
whole payload must be resent.
● What's LPM?
○ Longest Prefix Match for subnets.
● What's DHCP?
○ Automatic IP assignment on networks.

14. IP
● What's CIDR?
● How does DHCP change in IPv6?
● How is IPv6 different from IPv4?

15. IP
● What's CIDR?
○ Fine-grained IP block allocation
● How does DHCP change in IPv6?
○ IPv6 can autoconfigure IPs from MACs.
● How is IPv6 different from IPv4?
○ Bigger address space!
○ Extension headers!

16. Intra-domain Routing
● What's an AS?
● How does it manage its routing?

17. Intra-domain Routing
● What's an AS?
○ Autonomous system that manages its
own routing independently.
● How does it manage its routing?
○ OSPF: Link-state.
○ RIP: Distance-vector.
■ Problems?

18. BGP
● How does BGP operate?
● Does BGP emphasize optimality?

19. BGP
● How does BGP operate?
○ Advertisements about routes through
ASes.
● Does BGP emphasize optimality?
○ No! Emphasizes policy, often
influenced by money, companies,
contracts, etc.

20. Physical Layer
● What's a signal?
● What's a bit?
● What's a chip?
● Why chips?

21. Physical Layer
● What's a signal?
○ Actual voltages sent along wire or
through air.
● What's a bit?
○ Quanta of information above physical
layer.
● What's a chip?
○ Physical layer "bit."
● Why chips?
○ Multiple chips per bit for error checking.

22. DNS
● Purpose?
● Are DNS servers optimized for reading or
writing?
● Are DNS servers quick to update?
● What's a glue record and where are they?
● How can DNS be compromised?

23. DNS
● Purpose?
○ Map names to IPs.
● Are DNS servers optimized for reading or writing?
○ Reading - domain names requested far, far more
than changed.
● Are DNS servers quick to update?
○ Slow - data aggressively cached.
● What's a glue record and where are they?
○ Informs of name servers one level lower, in
ADDITIONAL + AUTHORITY section of DNS
reply.
● How can DNS be compromised?
○ Timing attack, exploitation of glue/A record trust.