CSEE W4140 Networking Laboratory Opening Lecture Jong Yul Kim

Computer Science in one word Abstraction “a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a time” - wikipedia

Figure from Computer Networking: a top down approach

INTERNET

Details Figure from “Google: A Behind-the-Scenes Tour” by Jeff Dean

Reality Figure from “Google: A Behind-the-Scenes Tour” by Jeff Dean

Real Network Protocols “RIP is a distance-vector protocol that operates in a manner very close to the idealized DV protocol we examined” -Computer Networking: A Top-Down Approach 4/e

Course Objectives  The main idea: learning by doing Build a network using PCs, routers, cables Configure them properly Run the experiment Observe real network protocol behavior Gather data Analyze and evaluate  Explore how abstract concepts are designed to work in real life and to observe how they really behave

Course Objectives  Reinforce your knowledge of networks  Gain first-hand experience and skills  Learn how to use Linux for networks  Pre-requisite Computer Networks or equivalent

Required Textbook Mastering Networks: An Internet Lab Manual (= The Manual) You must have The Manual! One reserved copy in the Engineering library.

Lab sequence

Lab Organization  Each lab has three parts Prelab HW - individually Lab session Lab report  You need to bring Your Lab Manual A USB drive to store your data in groups of two

Lab Times  Tuesdays 10 am ~ 12 pm  Tuesdays 4:10 ~ 6:40 pm  Wednesdays 10 am ~ 12 pm This one might be changed.  10 students in each lab time  Please sign up!

Lab Equipment

Lectures  Mondays 2:30 ~ 4:00 pm at 327 Mudd  Go over topics in the upcoming lab  Discussions on reading assignments  Review of relevant Computer Networks material

Grading Prelab HW10% Lab performance & Lab reports60% Midterm10% Final10% In-class quiz & Participation10% Open-book, open-notes, open to quiet discussions

Homework Policy  Prelab HW Individual work Due every Friday at 11:59 pm Don’t copy and paste from other sources  Lab reports Team work Due before next lab Don’t turn in 100 page reports! Avg. 5~20

Academic Honesty Policy  Summary: Do your own work.  Do not copy other’s homework (past or current students).  Do not copy and paste from wikipedia or any other source including textbooks, web sites, etc.  If you cannot think of another way to explain your answer, you should give proper credit to the source.

Homework Policy  Late submission 20 points deducted per day But you can use 3 late days  At most 1 week for reconsideration after grades are announced

Contact and Office Hours  Instructor Jong Yul Kim TBA after lab sessions are fixed.  TAs Kyung Wha Kim (kk2515) Varun Mahendra (vum2001) Third TA (???)

How to fail this class quickly #1 Connect any lab machine to the Internet. ALWAYS be careful and ask yourself before you plug it in: “Where is the other end of the cable?”

How to fail this class quickly #2 Leave the door to CRF open. ALWAYS keep CRF entrance closed. Lab doors can be open while you’re in the lab.

To get the most out of this course  Prepare for labs in advance Read the lab manual beforehand If you’re not familiar with something in the lab, consult textbook, ask me or TAs during office hours or by Submit your prelab HW on time  Come to class

Review of Important Concepts The following slides are from the texbook’s authors. Some content have been modified to fit this class.

Layers  The complexity of the communication task is reduced by using multiple protocol layers:  Each protocol is implemented independently  Each protocol is responsible for a specific subtask  Protocols are grouped in a hierarchy  A structured set of protocols is called a communications architecture or protocol suite

TCP/IP Protocol Suite  The TCP/IP protocol suite is the protocol architecture of the Internet  The TCP/IP suite has four layers: Application, Transport, Network, and Data Link Layer  End systems (hosts) implement all four layers. Gateways (Routers) only have the bottom two layers.

Functions of the Layers  Data Link Layer: Service: Reliable transfer of frames over a link Media Access Control on a LAN Functions: Framing, media access control, error checking  Network Layer: Service: Move packets from source host to destination host Functions: Routing, addressing  Transport Layer: Service: Delivery of data between hosts Functions: Connection establishment/termination, error control, flow control  Application Layer: Service: Application specific (delivery of , retrieval of HTML documents, reliable transfer of file) Functions: Application specific

TCP/IP Suite and OSI Reference Model The TCP/IP protocol stack does not define the lower layers of a complete protocol stack

Assignment of Protocols to Layers

Layered Communications

Service Primitives N+1 Layer Entity N Layer Entity N+1 Layer Peer Protocol Request Delivery Indicate Delivery Communication services are invoked via function calls. The functions are called service primitives

Service Primitives Recall: A layer N+1 entity sees the lower layers only as a service provider Service Provider N+1 Layer Entity N+1 Layer Peer Protocol Request Delivery Indicate Delivery

Service Access Points  A service user accesses services of the service provider at Service Access Points (SAPs)  A SAP has an address that uniquely identifies where the service can be accessed

Layers in the Example

Layers and Services  Service provided by TCP to HTTP: reliable transmission of data over a logical connection  Service provided by IP to TCP: unreliable transmission of IP datagrams across an IP network  Service provided by Ethernet to IP: transmission of a frame across an Ethernet segment  Other services: DNS: translation between domain names and IP addresses ARP: Translation between IP addresses and MAC addresses

Encapsulation and Demultiplexing  As data is moving down the protocol stack, each protocol is adding layer-specific control information

Encapsulation and Demultiplexing in our Example  Let us look in detail at the Ethernet frame between Argon and the Router, which contains the TCP connection request to Neon.  This is the frame in hexadecimal notation. 00e0 f923 a820 00a e c 9d bff 808f f b b e b4

Encapsulation and Demultiplexing

Encapsulation and Demultiplexing: Ethernet Header

Encapsulation and Demultiplexing: IP Header

Encapsulation and Demultiplexing: TCP Header Option: maximum segment size

Encapsulation and Demultiplexing: TCP Header

Encapsulation and Demultiplexing: Application data No Application Data in this frame

Main Points of Lab 1  Getting acquainted Hardware setup Linux Network tools (ping, tcpdump, wireshark)  Lab reports How to capture data What to include / exclude in lab reports

Homework  Prelab 1 & 2 due on Friday ( )  Lab report 1 due by next week  Read RFC 826 by next class