TCPIP Lecture 2

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TCP/IPLecture 2

• cs193i Internet Technologies
• Summer 2004
• Stanford University

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Announcements

• Lab 1 due Wednesday
• HW 1 assigned
• Extra perl session tomorrow
• Tuesday, June 29, 215-305pm, Skilling 193
• Broadcast live on E2, Stanford Online
• Silas Thursday office hours moved to Wednesday
  this week
• Sweet Hall, 630-830pm

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Communicating with Anyone
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Local Area Network (LAN)

• High speed, data network over small region
• Few thousand meters
• Network technologies
• Ethernet
• FDDI
• Token ring
• Data link layer
• Packets routed based on physical address (MAC)

LAN 1
LAN 2
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Local Area Network (LAN)

• High speed, data network over small region
• Few thousand meters
• Network technologies
• Ethernet
• FDDI
• Token ring
• Data link layer
• Packets routed based on physical address (MAC)

LAN 1
?
LAN 2
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Connecting Below Internet Level

• Hub
• Center of star topology
• In Ethernet, multiport repeater or concentrator
• Bridge
• Connects 2 networks of same technology extended
  LAN
• Filters/forwards/floods based on MAC
• Link layer - frames
• Switch
• Connects 2 networks packet-switched network
• Reduces collisions

Hub
Bridge
Switch
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Connecting at the Internet Level

• Router
• Originally gateway
• Forwards packets based on network layer info (IP)
• Separate broadcast domains
• In each domain, IP packet encapsulated in
  domain-specific packet

Router
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Internet Society

• Governing body for Internet since 1992
• http//www.isoc.org
• Domain names and addresses assigned
• Upper level Internet Assigned Numbers Authority
• Regional
• Latin America / Caribbean
• Asia Pacific
• America
• Europe

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How Does Everyone Work Together?

• Networks
• MCI Worldcom, Sprint, Earthlink,
• Exchange points provide connections between
  networks
• Network Access Points open access policies
• Network Service Provider
• Build national or global networks
• Lease space at NAPs
• Sell bandwidth to regional NSPs
• Regional NSP sell bandwidth to ISP
• Internet Service Provider sells bandwidth to end
  users

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How Does Everyone Work Together?
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OSI Reference Model for Network Design
Application (Layer 7) Presentation Session Transpo
rt Network Data Link Physical (Layer 1)
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OSI vs. TCP/IP Stack
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Internet Protocol
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IP Datagram
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IP Addresses

• 4 8-bit numbers (Hierarchical)
• Specifies both network and host
• Number of bits allocated to specify network
  varies
• Three classes

18.26.0.1
host
network
32-bits
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IP Addresses

• IP (Version 4) Addresses are 32 bits long
• IP Addresses Assigned Statically or Dynamically
  (DHCP)
• IPv6 addresses are 128 bits long

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IP Address Space

• Originally, 3 Classes
• A, B, C
• Problem
• Classes too rigid (C too small, B too big)
• Solution
• Subnetting (e.g. within Stanford)
• Classless Interdomain Routing (CIDR)

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Subnetting

• IP Address plus subnet mask (netmask)
• IP Addr 171.64.15.82Netmask 0xFFFFFF00
  (111...1100000000)
• First 24 bits are the Subnet ID (the
  neighborhood)
• Last 8 bits are Host ID (the street address)
• Can be written as Prefix Length
• 171.64.15.0/24 or 171.64.15/24

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Subnetting at Stanford
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IP Routing

• Routers are not omniscient
• Next-Hop
• Hop-by-Hop
• Thus IP makes no guarantees
• except to try its best (Best Effort)
• packets may get there out of order, garbled,
  duplicated
• may not get there at all!
• Unreliable datagram service

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IP Routing Hop-by-Hop
How a Router Forwards Datagrams
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Classless Interdomain Routing (CIDR)
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Classless Interdomain Routing (CIDR)
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Classless Interdomain Routing (CIDR)
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Classless Interdomain Routing (CIDR)
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Five Minute Break
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Network Programs

• host
• ping
• traceroute
• nslookup

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Summary of IP

• Connectionless/Datagram
• Unreliable/Best Effort

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Transmission Control Protocol
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Characteristics

• Connection-Oriented
• Reliable
• Byte-Stream
• Flow Control (aka Congestion Control)

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Three Phases

• Establish Connection
• Data Transfer
• Terminate Connection

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Establishing the Connection
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Data Transfer
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Data Transfer
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Maintaining the Connection
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Terminating the Connection
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• Connection-Oriented
• Reliable
• Byte-Stream
• Flow Control (aka Congestion Control)

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Reliability Flow Control

• Sequence numbers Acknowledgements (ACKs)
• Receiver detects Corrupt, Lost, Duplicated,
  Out-of-order
• Tell sender which packets it has received
  correctly
• Sender can resend
• In Flight Window (Window Size)
• Sender only has N unacknowledged packets in

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Sending a Message
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• Connection-Oriented
• Reliable
• Byte-Stream
• Flow Control (aka Congestion Control)

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UDP
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User Datagram Protocol (UDP)

• Like TCP, in the Transport Layer
• Characteristics
• Connectionless, Datagram, Unreliable
• Adds only application multiplexing/demultiplexing
  and checksumming to IP
• Good for Streaming Media, Real-time Multiplayer
  Networked Games, VoIP

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Summary

• IP is the basis of Internetworking
• TCP builds on top of IPadds reliable,
  congestion-controlled, connection-oriented
  byte-stream.
• UDP builds on top of IPallows access to IP
  functionality