TCP/IP
Lecture 2
cs193i – Internet Technologies
Summer 2004
Stanford University
Announcements
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Lab #1 due Wednesday
HW #1 assigned
Extra perl session tomorrow
Tuesday, June 29, 2:15-3:05pm, Skilling 193
 Broadcast live on E2, Stanford Online
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
Silas’ Thursday office hours moved to
Wednesday this week
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Sweet Hall, 6:30-8:30pm
Communicating with Anyone
How’s the
weather in
Seattle, Mar?
kashaw@cs.stanford.edu
Ethernet
Network
Tokenring
MSN Messenger
mar@cs.washington.edu
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What is FDDI?
Fiber Data Distributed Interface (FDDI) is a fiber-optic
networking technology utilizing a ring topology to provide
local area network connectivity at up to 200 Mbps.
FEATURES
Fiber Optic Connections
Single or Dual Ring Topology
Token passing for media access control
100 Mbps or 200 Mbps
4,352 byte frame size
Ring sizes in miles
Dual Ring
Counter rotating
What is FDDI Functions?
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FUNCTION
Media Access Control (MAC)
Physical Layer (PHY)
Physical Layer, Medium Dependant (PMD)
Station Management (SMT)
Concepts of FDDI Operation
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FDDI utilizes fiber optic technology as the
communications media. FDDI transmits light through
glass or clear plastic strands that are thinner than a
human hair. These strands carry signals from place to
place and are connected to laser-light emitters. The
strands are lit and unlit to provide data communication.
This makes FDDI very expensive however, and so you
rarely see it in a computer LAN. You will more often
see it in a cross campus network, but even this too is
fading with the advent of gigabit fiber-optic ethernet
(gig-e)
Local Area Network (LAN)
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High speed, data
network over small
region
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Network technologies:
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Few thousand meters
Ethernet
FDDI
Token ring
LAN 1
Ethernet
Tokenring
Data link layer
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Packets routed based on
physical address (MAC)
LAN 2
Local Area Network (LAN)
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High speed, data
network over small
region
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Network technologies:
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Few thousand meters
Ethernet
FDDI
Token ring
LAN 1
Ethernet
?
Tokenring
Data link layer
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Packets routed based on
physical address (MAC)
LAN 2
What is Data Link Layer DLL?
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Data Link Layer Sublayers: Logical Link Control
(LLC) and Media Access Control (MAC)
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What is Data Link Layer Functions?
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Logical Link Control (LLC): Logical link
control refers to the functions required for the
establishment and control of logical links between
local devices on a network.
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Media Access Control (MAC): This refers to the
procedures used by devices to control access to the
network medium.
Data Framing: The data link layer is responsible for the
final encapsulation of higher-level messages into frames
that are sent over the network at the physical layer.
Addressing: The data link layer is the lowest layer in the
OSI model that is concerned with addressing: labeling
information with a particular destination location.
Error Detection and Handling: The data link layer
handles errors that occur at the lower levels of the
network stack. For example, a cyclic redundancy check
(CRC) field is often employed to allow the station
receiving data to detect if it was received correctly.
What is CAM table?
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CAM Table
Content addressable memory (CAM) table is a
term referring to the dynamic content-addressable
memory in an Ethernet switch.
What is the operation of CAM?
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A Ethernet switch's role is to copy Ethernet
frames from one port to another. The presence of
a CAM table is one attribute)‫ ( صفة‬that
differentiates) ‫ ( للتفرقة بين‬a switch from a hub.
Without a functional CAM table, all frames
received by a network switch would be echoed
back out to all other ports, much like an Ethernet
hub. A switch should only emit a frame on the
port where the destination network device resides
(unicast), unless the frame is for all nodes on the
switch (broadcast) or multiple nodes (multicast).
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Generally, the CAM table is a system memory
construct used by Ethernet switch logic to
dereference ) ‫ (يوصل‬Media Access Control
(MAC) addresses of stations to the ports on which
they connect to the switch. This allows switches to
facilitate communications between connected
stations at high speed regardless of how many
devices are connected to the switch.
The CAM table is consulted to make the frame
forwarding decision. Switches learn MAC addresses
from the source address of Ethernet frames on the
ports, such as Address Resolution Protocol
response packets.
What is MAC?
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Media Access Control (MAC) technology
provides unique identification and access control
for computers on an Internet Protocol (IP)
network.
What is MAC address?
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Short for Media Access Control address,
Media Access Control assigns a unique number to
each IP network adapter called the MAC
address. A MAC address is 48 bits long. The
MAC address is commonly written as a sequence
of 12 hexadecimal digits as follows:
48-3F-0A
-91-00-BC
Manufacturing company
serial number
What is MAC flooding
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In a typical MAC flooding attack, a switch is fed
many Ethernet frames, each containing different
source MAC addresses, by the attacker. The
intention is to consume the limited memory set
aside in the switch to store the MAC address
table
Connecting Below Internet Level
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Hub
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Bridge
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Center of star topology
In Ethernet, multiport repeater
or concentrator
Connects 2 networks of same
technology – extended LAN
Filters/forwards/floods based
on MAC
Link layer - frames
Hub
Ethernet
Ethernet
Bridge
Switch
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Connects 2+ networks –
packet-switched network
Reduces collisions
Ethernet
Ethernet
CISCOSYSTEMS
CISCOSYSTEMS
T3
Switch
CISCOSYSTEMS
STS-N
Connecting at the Internet Level
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Router
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Originally gateway
Forwards packets based
on network layer info (IP)
Separate broadcast
domains
In each domain, IP packet
encapsulated in domainspecific packet
Ethernet
Ethernet
CISCOSYSTEMS
CISCOSYSTEMS
Router
CISCOSYSTEMS
Tokenring
Internet Society
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Governing body for Internet since 1992
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http://www.isoc.org
Domain names and addresses assigned
Upper level: Internet Assigned Numbers Authority
 Regional:
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Latin America / Caribbean
 Asia Pacific
 America
 Europe
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How Does Everyone Work
Together?
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Networks
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Network Service Provider
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MCI Worldcom, Sprint, Earthlink, …
Exchange points provide connections between networks
Network Access Points – open access policies
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
How Does Everyone Work
Together?
OSI Reference Model
for Network Design
Application (Layer 7)
Presentation
Session
Transport
Network
Data Link
Physical (Layer 1)
OSI vs. TCP/IP Stack
Layering: FTP Example
Application
Presentation
FTP
Application
ASCII/Binary
Session
Transport
Network
Link
Physical
The 7-layer OSI Model
TCP
Transport
IP
Network
Ethernet
Link
The 4-layer Internet model
Internet Protocol
Protocol Stack
App
Transport
TCP / UDP
Network
IP
Link
Data
Data
TCP Segment
Hdr
Hdr
IP Datagram
IP Datagram
Header
10101011101010101010010101010100101010100
11010010101010010101111111010000011101111
10100001011101010100110101011110100000101
00100000000010101000011010000111111010101
......... 1011011001010100011001001010110
Data
IP Addresses
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4 8-bit numbers (Hierarchical)
18.26.0.1
network
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32-bits
host
Specifies both network and host
Number of bits allocated to specify network varies
Three classes:
A
0 net
1 7
B
host
24 bits
C
1 0 net
host
110
net
host
2
16 bits
3
21
8 bits
14
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
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Originally, 3 Classes
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Problem
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A, B, C
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: 171.64.15.82
Netmask: 0xFFFFFF00 (111...1100000000)
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 First
24 bits are the Subnet ID (the
neighborhood)
 Last 8 bits are Host ID (the street address)
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Can be written as “Prefix + Length”
 171.64.15.0/24
or 171.64.15/24
Subnetting at Stanford
To: cenic.net
dcl-rtr
171.64.74.0/24
171.64.1.132
171.64.1.132/30
171.64.1.133
Stanford Class B
Address
171.64.1.161 171.64.1.178
bbr2-rtr
171.64.0.0/16
171.64.1.160/27
171.64.1.152
171.64.1.144/28
To: cogentco.com border-rtr
171.64.1.145
171.64.74.1
Gates-rtr
171.64.74.58
yuba
IP Routing
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Routers are not omniscient
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Next-Hop
Hop-by-Hop
Thus IP makes no guarantees
except to try it’s 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
128.17.20.1
1
R1 2
3
R2
R3
R4
128.17.16.1
e.g. 128.9.16.14 => Port 2
Prefix
65/8
128.9/16
128.9.16/20
128.9.19/24
128.9.25/24
128.9.176/20
142.12/19
Next-hop
128.17.16.1
128.17.14.1
128.17.14.1
128.17.10.1
128.17.14.1
128.17.20.1
128.17.16.1
Port
3
2
2
7
2
1
3
Forwarding/routing table
How a Router Forwards Datagrams
Classless Interdomain Routing
(CIDR)
0
232-1
Classless Interdomain Routing
(CIDR)
128.9.0.0
65/8
0
128.9.16.14
142.12/19
128.9/16
216
232-1
Classless Interdomain Routing
(CIDR)
128.9.19/24
128.9.25/24
128.9.16/20 128.9.176/20
128.9/16
0
232-1
128.9.16.14
Classless Interdomain Routing
(CIDR)
128.9.19/24
128.9.25/24
128.9.16/20 128.9.176/20
128.9/16
0
232-1
128.9.16.14
Five Minute Break
Network Programs
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host
ping
traceroute
nslookup
Summary of IP
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Connectionless/Datagram
Unreliable/Best Effort
Transmission Control Protocol
Protocol Stack
App
Transport
TCP / UDP
Network
IP
Link
Data
Data
TCP Segment
Hdr
Hdr
IP Datagram
Characteristics
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Connection-Oriented
Reliable
Byte-Stream
Flow Control
(aka Congestion Control)
Three Phases
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Establish Connection
Data Transfer
Terminate Connection
Establishing the Connection
(Active)
Client
Syn
(Passive)
Server
Syn + Ack
Ack
Connection Setup
3-way handshake
Data Transfer
Host A
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
Host B
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
Data Transfer
Host A
TCP Data
Host B
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
TCP Data
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
Maintaining the “Connection”
IP Data
TCP Data
0
TCP Hdr
15
Src port
31
Dst port
Sequence #
Ack Sequence #
RSVD
6
Flags
URG
ACK
PSH
RST
SYN
FIN
HLEN
4
Checksum
IP Hdr
Window Size
Urg Pointer
(TCP Options)
TCP Data
Src/dst port numbers
and IP addresses
uniquely identify socket
Terminating the Connection
(Active)
Client
Fin
(Passive)
Server
(Data +) Ack
Fin
Ack
Connection Close/Teardown
2 x 2-way handshake
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Connection-Oriented
Reliable
Byte-Stream
Flow Control
(aka Congestion Control)
Reliability & Flow Control
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Sequence numbers & Acknowledgements
(ACKs)
Receiver detects Corrupt, Lost, Duplicated, Out-oforder
 Tell sender which packets it has received correctly
 Sender can resend
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In Flight Window (Window Size)
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Sender only has N unacknowledged packets “in
Sending a Message
Leland.Stanford.edu
Application Layer
Arachne.Berkeley.edu
Leslie
Ron
Transport Layer
O.S.
D
Data
Header
Data
O.S.
Header
Network Layer
H
D
H
D
D
H
H
D
D
H
Link Layer
H
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Connection-Oriented
Reliable
Byte-Stream
Flow Control
(aka Congestion Control)
UDP
Protocol Stack
App
Transport
TCP / UDP
Network
IP
Link
Data
Data
TCP Segment
Hdr
Hdr
IP Datagram
User Datagram Protocol (UDP)
Like TCP, in the Transport Layer
 Characteristics
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 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
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IP is the basis of Internetworking
TCP builds on top of IP
adds reliable, congestion-controlled, connectionoriented byte-stream.
UDP builds on top of IP
allows access to IP functionality