Johns Hopkins · EN.601.414 · Fall 2023

General

Course Overview

• What is a computer network? What is the internet?

Application Layer

• What is the four layer internet model?
• What is the client-server paradigm?
• What is peer-to-peer architecture?
• What is the hypertext transport protocol (HTTP)?
• What's in a HTTP request or response message?
• How do you maintain state with HTTP (i.e., what are cookies)?
• What are the performance goals of HTTP, what are the Three "P"s to achieve them, and how is performance measured?

Content Distribution Network

• What is caching?
• What are reverse and forward proxies?
• What are content distribution networks?
• What are the server selection methods?

Domain Name System

• What is machine address, machine name, and DNS?
• What are the other directory design choices? What is "flood the query"?
• What are the goals of the DNS?
• What is hierarchical namespace?
• What is hierarchical administration?
• What is the server hierarchy? Who manages the top-level directory server or the authoritative DNS servers?
• What is anycast?
• What are DNS resource records, and what are the types? How do you insert resource records into DNS?
• What is the relationship between local DNS servers and client applications?
• What is the difference between recursive and iterative name resolution?
• What are the components of a DNS query and reply message?
• How is replication done with DNS servers?
• What is and how is caching and negative caching done in DNS?
• What is the mapping between names and addresses? What is "indirection"?

Transport Layer

Intro to the Transport Layer

• What is the need for the transport layer? What is its role?
• What is multiplexing and demultiplexing?
• What are sockets and ports?
• What is the user diagram protocol (UDP)?
• What does it mean to have reliable transport? What do the following mechanisms do: checksum, ACKs, NACKs, sequence numbers, retransmission, timeouts?
• What is the "Stop and Wait" reliable transport solution?
• What is a sliding window? What is cumulative vs selective ACKs? What is Go-Back-N vs Selective Repeat?

TCP

• What are the contents in a TCP header?
• What is a TCP Segment?
• How are sequence numbers specified when sending and acknowledging data? What is fast retransmit and how are they related?
• What is a retransmission timeout?
• How do you estimate RTT? What is Karn/Partidge Algorithm and Kacobson/Karels Algorithm?
• How to establish connection with TCP? What is the 3-way handshake? What happens when the initial SYN packet is lost?
• How are connections torn down? What is the difference between normal and abrupt termination?

Flow Control

• What is the idea of flow control? Why is it needed?
• What is an advertised window (RWND)? What is the difference between the sliding window and advertised window?

Congestion Control

• What is congestion? What was the congestion collapse?
• What was Jacobson's fix to TCP congestion? What is the difference between CWND, RWND, and Sender-side Window?
• How do we detect congestion in the network?
• How do we adjust rate?
• What is slow start? How does the slow start phase begin, when does it stop, and how does it adjust to varying bandwidth?
• What is the congestion avoidance phase?
• How do you implement congestion control?
• What is fast recovery?
• What are other TCP flavors?

Network Layer

Intro to the Network Layer

• What is the network layer?
• What are autonomous systems, border routers, interior routers, routes, and end hosts?
• What is forwarding and routing?

IP

• What is an IP packet?
• What is in a IP header and what are its goals?
• What is fragmentation?
• How is fragmentation implemented in the IP header?

Switched Networks

• What is circuit switching?
• What are the circuit types and how do they differ?
• What is packet switching?

Network Addresses

• What is an IP address?
• What is a LAN or WAN?
• What is hierarchical addressing and what does it provide?
• What is classless inter-domain routing (CIDR)?
• What is IPv6?

Routers

• What is a router and how do you calculate its capacity?
• What is inside a router?
• How do input linecards look up the output port from a destination address?
• What does switching fabric do and how does it switch?
• What does an output linecard do? What are the buffer management techniques?
• What is packet scheduling and what are the four scheduling policies?
• What is router-assisted congestion control?
• What is explicit congestion notification (ECN)?
• What is random early detection (RED)?

Routing

• What is routing and its goal?
• What is the difference between local and global routing state?
• How do you know a routing state is valid?
• What is least-cost path routing and what is a protocol that implements it?
• What is Dijkstra's Algorithm?
• What is link-state routing protocol, flooding, and convergence?
• What is the distance-vector routing and what is a protocol that implements it?
• What is the count-to-infinity scenario and what is the poisoned reverse heuristic?
• What are the differences and similarities between link-state and distance-vector routing?

BGP

• What are relationships between autonomous systems?
• What is BGP?
• What is a BGP Policy?
• What are the Gao-Rexford rules?
• What does it mean to "speak BGP"?
• What is eBGP, iBGP, IGP?
• What are the four basic messages in BGP?
• What are route attributes and what are the four standard attributes?
• What are the issues with BGP?

Software Defined Networks

• What is the data and control plane of a traditional computer network?
• What are main frames and routers/switches?
• What is a software defined network and what problem does it address?
• What are the benefits of programmable switches?
• What is P4 language?

Link Layer

Intro to the Link Layer

• What is the data link layer and what are its four primary services?
• What are frames and mediums that data can go through?
• How do you support multiple access in a shared broadcast channel? What are the three classes of technique? What is the random access
• What is carrier sense multiple access (CSMA) and what does it mean to have collision detection?
• What is the difference between broadcast ethernet and switched ethernet? What are the advantages of a switched ethernet?
• What are ethernet frames? What is the framing problem? What does it mean to frame with sentinel bits?
• What is a medium access control (MAC) address?
• What is an ethernet switch? What is a switch table? What does it mean for it to be self learning?
• What are the discovery protocols in the link layer?
• What is Dynamic Host Configuration Protocol (DHCP)?
• What is Address Resolution Protocol (ARP)? How does it differ from DHCP?
• What are virtual LANs? What is a trunk port?

Wireless Networks

• What are the elements of a wireless network?
• What are the characteristics of wireless links
• How do you deal with bit errors in a wireless network?
• What is CSMA/CA?
• What is 802.11 wireless LAN?
• What is the hidden terminal problem?

Review

Midterm Review

Others

Security

• What are security risks with TCP What is the risk with a TCP abrupt termination? What is a TCP RST injection? What is connection Hijacking?
• What is SSL and what does it provide?
• What are security concerns with IP? What is a denial of service attack? What is spoofing? How can IP options be misused? How can ToS be used to attack traffic? What are the security implications of fragmentation? What is a state-holding attack? What are the security implications of TTL?
• What are network layer threats? What is IPsec? What is a VPN?
• What are physical and link layer Issues? What is eavesdropping or sniffing? What are some DHCP vulnerabilities?

Datacenters

• What is cloud computing?
• What is in a datacenter?
• What does a datacenter network look like?
• What are the challenges of datacenter networks?
• What is partition-aggregation traffic?
• What are data center workload types?
• What is incast?
• What are datacenter transport requirements?
• What is datacenter TCP and how is it different from TCP?