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TCP/IPTCP/IPLecture 2Lecture 2
cs193i – Internet cs193i – Internet TechnologiesTechnologies
Summer 2004Summer 2004
Stanford UniversityStanford University
AnnouncementsAnnouncements
Lab #1 due WednesdayLab #1 due Wednesday HW #1 assignedHW #1 assigned Extra perl session tomorrowExtra perl session tomorrow
Tuesday, June 29, 2:15-3:05pm, Skilling Tuesday, June 29, 2:15-3:05pm, Skilling 193193
Broadcast live on E2, Stanford OnlineBroadcast live on E2, Stanford Online Silas’ Thursday office hours moved to Silas’ Thursday office hours moved to
Wednesday this weekWednesday this week Sweet Hall, 6:30-8:30pmSweet Hall, 6:30-8:30pm
Communicating with Communicating with AnyoneAnyone
Token-ring
mar@cs.washington.edu
kashaw@cs.stanford.edu
How’s theweather inSeattle, Mar?
MSN Messenger
Network
Ethernet
Local Area Network Local Area Network (LAN)(LAN)
High speed, data High speed, data network over small network over small regionregion Few thousand metersFew thousand meters
Network Network technologies:technologies: EthernetEthernet FDDIFDDI Token ringToken ring
Data link layer Data link layer Packets routed based Packets routed based
on physical address on physical address (MAC)(MAC)
Ethernet
Token-ring
LAN 1
LAN 2
Local Area Network Local Area Network (LAN)(LAN)
High speed, data High speed, data network over small network over small regionregion Few thousand metersFew thousand meters
Network Network technologies:technologies: EthernetEthernet FDDIFDDI Token ringToken ring
Data link layer Data link layer Packets routed based Packets routed based
on physical address on physical address (MAC)(MAC)
Ethernet
Token-ring
LAN 1
LAN 2
?
Connecting Below Connecting Below Internet LevelInternet Level
HubHub Center of star topologyCenter of star topology In Ethernet, multiport In Ethernet, multiport
repeater or concentratorrepeater or concentrator BridgeBridge
Connects 2 networks of Connects 2 networks of same technology – same technology – extended LANextended LAN
Filters/forwards/floods Filters/forwards/floods based on MAC based on MAC
Link layer - framesLink layer - frames SwitchSwitch
Connects 2+ networks – Connects 2+ networks – packet-switched packet-switched networknetwork
Reduces collisionsReduces collisions
Ethernet Ethernet
Hub
Bridge
Switch
Ethernet Ethernet
CISCOSYSTEMS
CISCOSYSTEMS CISCOSYSTEMS
T3 STS-N
Connecting at the Connecting at the Internet LevelInternet Level
RouterRouter Originally gatewayOriginally gateway Forwards packets Forwards packets
based on network based on network layer info layer info (IP)(IP)
Separate broadcast Separate broadcast domainsdomains
In each domain, IP In each domain, IP packet encapsulated packet encapsulated in domain-specific in domain-specific packetpacket
Token-ring
CISCOSYSTEMS
Ethernet
CISCOSYSTEMS
Ethernet
CISCOSYSTEMS
Router
Internet SocietyInternet Society
Governing body for Internet since 1992Governing body for Internet since 1992 http://www.isoc.orghttp://www.isoc.org
Domain names and addresses assignedDomain names and addresses assigned Upper level: Internet Assigned Numbers Upper level: Internet Assigned Numbers
AuthorityAuthority Regional: Regional:
Latin America / CaribbeanLatin America / Caribbean Asia PacificAsia Pacific AmericaAmerica EuropeEurope
How Does Everyone Work How Does Everyone Work Together?Together?
NetworksNetworks MCI Worldcom, Sprint, Earthlink, …MCI Worldcom, Sprint, Earthlink, … Exchange points provide connections between Exchange points provide connections between
networksnetworks Network Access Points – open access policiesNetwork Access Points – open access policies
Network Service Provider Network Service Provider Build national or global networksBuild national or global networks Lease space at NAPsLease space at NAPs Sell bandwidth to regional NSPsSell bandwidth to regional NSPs Regional NSP sell bandwidth to ISPRegional NSP sell bandwidth to ISP
Internet Service Provider sells bandwidth to Internet Service Provider sells bandwidth to end usersend users
How Does Everyone Work How Does Everyone Work Together?Together?
OSI Reference Model OSI Reference Model for Network Designfor Network Design
Application (Layer 7)Presentation
SessionTransportNetworkData Link
Physical (Layer 1)
OSI vs. TCP/IP StackOSI vs. TCP/IP Stack
Layering: FTP Example
Network
Link
Transport
Application
Presentation
Session
Transport
Network
Link
Physical
The 7-layer OSI Model The 4-layer Internet model
ApplicationFTP
ASCII/Binary
IP
TCP
Ethernet
Internet ProtocolInternet Protocol
App
Transport
Network
Link
TCP / UDP
IP
Data Hdr
Data Hdr
TCP Segment
IP Datagram
Protocol Stack
IP DatagramIP Datagram
Header
10101011101010101010010101010100101010100110100101010100101011111110100000111011111010000101110101010011010101111010000010100100000000010101000011010000111111010101......... 1011011001010100011001001010110
Data
IP AddressesIP Addresses 4 8-bit numbers (Hierarchical)4 8-bit numbers (Hierarchical)
Specifies both network and hostSpecifies both network and host Number of bits allocated to specify network Number of bits allocated to specify network
variesvaries Three classes:Three classes:
0 net host
1 7 24 bits
110 net host
3 21 8 bits
1 0 net host
2 14 16 bits
A B C
18.26.0.1
network 32-bits host
IP AddressesIP Addresses
IP (Version 4) Addresses are 32 bits IP (Version 4) Addresses are 32 bits longlong
IP Addresses Assigned Statically or IP Addresses Assigned Statically or Dynamically (DHCP)Dynamically (DHCP)
IPv6 addresses are 128 bits longIPv6 addresses are 128 bits long
IP Address SpaceIP Address Space
Originally, 3 ClassesOriginally, 3 Classes A, B, CA, B, C
ProblemProblem Classes too rigid (C too small, B too Classes too rigid (C too small, B too
big)big) SolutionSolution
Subnetting (e.g. within Stanford)Subnetting (e.g. within Stanford) Classless Interdomain Routing (CIDR)Classless Interdomain Routing (CIDR)
SubnettingSubnetting
IP Address plus subnet mask (netmask)IP Address plus subnet mask (netmask) IP Addr: 171.64.15.82IP Addr: 171.64.15.82
Netmask: 0xFFFFFF00 Netmask: 0xFFFFFF00 (111...1100000000)(111...1100000000) First 24 bits are the Subnet ID (the First 24 bits are the Subnet ID (the
neighborhood)neighborhood) Last 8 bits are Host ID (the street address)Last 8 bits are Host ID (the street address)
Can be written as “Prefix + Length”Can be written as “Prefix + Length” 171.64.15.0/24 or 171.64.15/24171.64.15.0/24 or 171.64.15/24
Subnetting at StanfordSubnetting at Stanford
Gates-rtr171.64.74.58
171.64.74.0/24
171.64.1.178
yuba
border-rtr
dcl-rtr
bbr2-rtr
171.64.1.161
171.64.1.160/27171.64.0.0/16
Stanford Class BAddress
171.64.74.1
171.64.1.132To: cenic.net
To: cogentco.com
171.64.1.152
171.64.1.145
171.64.1.133
171.64.1.144/28
171.64.1.132/30
IP RoutingIP Routing
Routers are not omniscientRouters are not omniscient Next-HopNext-Hop
Hop-by-HopHop-by-Hop Thus IP makes no guaranteesThus IP makes no guarantees
except to try it’s best (”Best Effort”)except to try it’s best (”Best Effort”) packets may get there out of order, packets may get there out of order,
garbled, duplicatedgarbled, duplicated may not get there at all!may not get there at all! Unreliable datagram serviceUnreliable datagram service
IP Routing Hop-by-HopIP Routing Hop-by-Hop
128.9/16128.9.16/20
128.9.176/20
128.9.19/24128.9.25/24
142.12/19
65/8
Prefix Port
3227213
128.17.14.1128.17.14.1
128.17.20.1
128.17.10.1128.17.14.1
128.17.16.1
128.17.16.1
Next-hop
R1
R2
R3
R4
12
3
128.17.20.1
128.17.16.1
e.g. 128.9.16.14 => Port 2
Forwarding/routing table
How a Router Forwards Datagrams
Classless Interdomain Classless Interdomain Routing (CIDR)Routing (CIDR)
0 232-1
Classless Interdomain Classless Interdomain Routing (CIDR)Routing (CIDR)
0 232-1
128.9/16
128.9.0.0
216
142.12/19
65/8
128.9.16.14
Classless Interdomain Classless Interdomain Routing (CIDR)Routing (CIDR)
0 232-1
128.9/16
128.9.16.14
128.9.16/20128.9.176/20
128.9.19/24
128.9.25/24
Classless Interdomain Classless Interdomain Routing (CIDR)Routing (CIDR)
0 232-1
128.9/16
128.9.16.14
128.9.16/20128.9.176/20
128.9.19/24
128.9.25/24
Five Minute Break Five Minute Break
Network ProgramsNetwork Programs
hosthost pingping traceroutetraceroute nslookupnslookup
Summary of IPSummary of IP
Connectionless/DatagramConnectionless/Datagram Unreliable/Best EffortUnreliable/Best Effort
Transmission Control Transmission Control ProtocolProtocol
App
Transport
Network
Link
TCP / UDP
IP
Data Hdr
Data Hdr
TCP Segment
IP Datagram
Protocol Stack
CharacteristicsCharacteristics
Connection-OrientedConnection-Oriented ReliableReliable Byte-StreamByte-Stream Flow Control Flow Control
(aka Congestion Control)(aka Congestion Control)
Three PhasesThree Phases
Establish ConnectionEstablish Connection Data TransferData Transfer Terminate ConnectionTerminate Connection
Establishing the Establishing the ConnectionConnection
Connection Setup3-way handshake
(Active)Client
(Passive)Server
Syn
Syn + Ack
Ack
Data TransferData Transfer
Byte 0
Byte 1
Byte 2
Byte 3
Byte 0
Byte 1
Byte 2
Byte 3
Host A
Host B
Byte 80
Byte 80
Data TransferData Transfer
Byte 0
Byte 1
Byte 2
Byte 3
Byte 0
Byte 1
Byte 2
Byte 3
Host A
Host B
Byte 80
TCP Data
TCP DataB
yte 80
Maintaining the Maintaining the “Connection”“Connection”
IP HdrIP Data
TCP HdrTCP Data
Src port Dst port
Sequence #
Ack Sequence #
HLEN
4
RSVD
6 UR
GA
CK
PS
HR
ST
SYN
FIN
FlagsWindow Size
Checksum Urg Pointer
(TCP Options)
0 15 31
TCP Data
Src/dst port numbersand IP addresses
uniquely identify socket
Terminating the Terminating the ConnectionConnection
Connection Close/Teardown2 x 2-way handshake
(Active)Client
(Passive)Server
Fin
(Data +) Ack
Fin
Ack
Connection-OrientedConnection-Oriented ReliableReliable Byte-StreamByte-Stream Flow Control Flow Control
(aka Congestion Control)(aka Congestion Control)
Reliability & Flow ControlReliability & Flow Control
Sequence numbers & Sequence numbers & Acknowledgements (ACKs)Acknowledgements (ACKs) Receiver detects Corrupt, Lost, Duplicated, Receiver detects Corrupt, Lost, Duplicated,
Out-of-order Out-of-order Tell sender which packets it has received Tell sender which packets it has received
correctlycorrectly Sender can resendSender can resend
In Flight Window (Window Size)In Flight Window (Window Size) Sender only has N unacknowledged Sender only has N unacknowledged
packets “inpackets “in
Sending a MessageSending a Message
Network Layer
Link Layer
Ron Leslie
Leland.Stanford.edu Arachne.Berkeley.eduApplication Layer
Transport Layer
O.S. O.S.HeaderData HeaderData
HD
HD
HD
HD HD
HD
Connection-OrientedConnection-Oriented ReliableReliable Byte-StreamByte-Stream Flow Control Flow Control
(aka Congestion Control)(aka Congestion Control)
UDPUDP
App
Transport
Network
Link
TCP / UDP
IP
Data Hdr
Data Hdr
TCP Segment
IP Datagram
Protocol Stack
User Datagram Protocol User Datagram Protocol (UDP)(UDP)
Like TCP, in the Transport LayerLike TCP, in the Transport Layer CharacteristicsCharacteristics
Connectionless, Datagram, UnreliableConnectionless, Datagram, Unreliable Adds only Adds only application application
multiplexing/demultiplexingmultiplexing/demultiplexing and and checksummingchecksumming to IP to IP
Good for Streaming Media, Real-Good for Streaming Media, Real-time Multiplayer Networked time Multiplayer Networked Games, VoIPGames, VoIP
SummarySummary
IP is the basis of InternetworkingIP is the basis of Internetworking TCP builds on top of IPTCP builds on top of IP
adds reliable, congestion-controlled, adds reliable, congestion-controlled, connection-oriented byte-stream.connection-oriented byte-stream.
UDP builds on top of IPUDP builds on top of IPallows access to IP functionalityallows access to IP functionality
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