CS代考程序代写 algorithm Java dns FTP 1/5/21

1/5/21
UCLA CS 118 Winter 2021
Instructor: Giovanni Pau TAs:
Hunter Dellaverson Eric Newberry
Introduction
Chapter 1 Introduction
A note on the use of these Powerpoint slides:
We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:
§ If you use these slides (e.g., in a class) that you mention their source
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§ If you post any slides on a www site, that you note that they are adapted
from (or perhaps identical to) our slides, and note our copyright of this material.
Thanks and enjoy! JFK/KWR
All material copyright 1996-2016
J.F Kurose and K.W. Ross, All Rights Reserved
Computer Networking: A Top Down Approach
7th edition
Jim Kurose, Keith Ross Pearson/Addison Wesley April 2016
1-2
12
Chapter 1: introduction
Chapter goal:
§Get “feel,” “big picture,” introduction to terminology
• more depth, detail later in course
Overview/roadmap:
§ What is the Internet? What is a protocol?
§ Network edge: hosts, access network, physical media
§ Network core: packet/circuit switching, internet structure
§ Performance: loss, delay, throughput
§ Protocol layers, service models
§ Security
§ History
Introduction: 1-3
The Internet: a “nuts and bolts” view
Billions of connected computing devices:
§ hosts = end systems
§ running network apps at Internet’s “edge”
Packet switches: forward packets (chunks of data)
§ routers, switches Communication links
§ fiber, copper, radio, satellite § transmission rate: bandwidth
Networks
§ collection of devices, routers, links: managed by an organization
mobile network
national or global ISP
home network
enterprise network
local or
regionIanl IStPernet
content provider network
datacenter network
Introduction: 1-4
34
1

The Internet: a “services” view
What’s a protocol?
Human protocols:
§ “what’s the time?” § “I have a question” § introductions
Rules for:
… specific messages sent … specific actions taken
when message received, or other events
§ Infrastructure that provides services to applications:
• Web, streaming video, multimedia teleconferencing, email, games, e- commerce, social media, inter- connected appliances, …
§ provides programming interface to distributed applications:
• “hooks” allowing sending/receiving apps to “connect” to, use Internet transport service
• provides service options, analogous to postal service
mobile network
Network protocols:
§ computers (devices) rather than humans § all communication activity in Internet
governed by protocols
Protocols define the format, order of messages sent and received among network entities, and actions taken
on message transmission, receipt
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“Fun” Internet-connected devices
Tweet-a-watt: monitor energy use
cars
scooters
Others?
Introduction: 1-5
bikes
Amazon Echo
IP picture frame
Slingbox: remote control cable TV
Pacemaker & Monitor
Web-enabled toaster + weather forecaster
Internet refrigerator
Security Camera
AR devices
Internet phones
Fitbit
Gaming devices
sensorized, bed mattress
The Internet: a “nuts and bolts” view
§ Internet: “network of networks” • Interconnected ISPs
§ protocols are everywhere
• control sending, receiving of
messages
• e.g., HTTP (Web), streaming video,
Skype, TCP, IP, WiFi, 4G, Ethernet
§Internet standards
• RFC: Request for Comments
• IETF: Internet Engineering Task Force
mobile network 4G
national or global ISP
Skype
IP
local or regional ISP
WiFi
Streaming video
home network
H T T P
Ethernet
enterprise network
content provider network
d a ne
TCP
Introduction: 1-6
tacent twork
e r
56
Skype
national or global ISP
Streaming video
datacenter network
Introduction: 1-7
local or regional ISP
home network
HTTP
enterprise network
content provider network
78
Introduction: 1-8
2

11
12
What’s a protocol?
A human protocol and a computer network protocol:
Chapter 1: roadmap
§ What is the Internet?
§ What is a protocol?
§ Network edge: hosts, access network, physical media
§ Network core: packet/circuit switching, internet structure
§ Performance: loss, delay, throughput
§ Security
§ Protocol layers, service models
§ History
Hi
Hi
Got the time? 2:00
TCP connection request
TCP connection response
GET http://gaia.cs.umass.edu/kurose_ross
time
Q: other human protocols?
9 10
A closer look at Internet structure
A closer look at Internet structure
Network edge:
§hosts: clients and servers §servers often in data centers
national or global ISP
Network edge:
§hosts: clients and servers §servers often in data centers
Access networks, physical media:
§wired, wireless communication links
national or global ISP
mobile network
mobile network
home network
enterprise network
content provider network
datacenter network
Introduction: 1-11
home network
enterprise network
content provider network
datacenter network
Introduction: 1-12
local or regional ISP
local or regional ISP
Introduction: 1-9
Introduction: 1-10
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13
14
15
16
A closer look at Internet structure
Access networks and physical media
Network edge:
§hosts: clients and servers §servers often in data centers
Access networks, physical media:
§wired, wireless communication links
Network core:
§interconnected routers §network of networks
national or global ISP
national or global ISP
Access networks: cable-based access
Access networks: cable-based access
cable modem
splitter
cable splitter modem
data, TV transmitted at different frequencies over shared cable distribution network
cable modem termination system
ISP
C
O VVVVVV N IIIIIIDDT DDDDDDAAR EEEEEETTO OOOOOOAAL
123456789 Channels
§ HFC: hybrid fiber coax
• asymmetric: up to 40 Mbps – 1.2 Gbps downstream transmission rate, 30-100 Mbps
frequency division multiplexing (FDM): different channels transmitted in different frequency bands
upstream transmission rate
§ network of cable, fiber attaches homes to ISP router
• homes share access network to cable headend
cable headend
cable headend
CMTS
mobile network
Q: How to connect end systems to edge router?
mobile network
home network
enterprise network
content provider network
datacenter network
Introduction: 1-13
home network
enterprise network
content provider network
datacenter network
Introduction: 1-14
local or regional ISP
§ §
§
residential access nets
institutional access networks (school, company)
mobile access networks (WiFi, 4G/5G)
local or regional ISP
……
Introduction: 1-15
Introduction: 1-16
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4

Access networks: digital subscriber line (DSL)
central office
DSLAM
DSL access multiplexer
telephone network
DSL splitter modem
voice, data transmitted at different frequencies over dedicated line to central office
ISP
§ use existing telephone line to central office DSLAM • data over DSL phone line goes to Internet
• voice over DSL phone line goes to telephone net
§24-52 Mbps dedicated downstream transmission rate §3.5-16 Mbps dedicated upstream transmission rate
Introduction: 1-17
Access networks: home networks
Wireless and wired devices
often combined in single box
WiFi wireless access point (54, 450 Mbps)
to/from headend or central office
cable or DSL modem
router, firewall, NAT wired Ethernet (1 Gbps)
Introduction: 1-18
17 18
Wireless access networks
Shared wireless access network connects end system to router § via base station aka “access point”
Wireless local area networks (WLANs)
§ typically within or around building (~100 ft)
§ 802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate
to Internet
Wide-area cellular access networks
§ provided by mobile, cellular network operator (10’s km)
§ 10’s Mbps
§ 4G cellular networks (5G coming)
to Internet
Introduction: 1-19
Access networks: enterprise networks
Ethernet switch
Enterprise link to ISP (Internet) institutional router
institutional mail, web servers
§ companies, universities, etc.
§ mix of wired, wireless link technologies, connecting a mix of switches
and routers (we’ll cover differences shortly)
§ Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps § WiFi: wireless access points at 11, 54, 450 Mbps
Introduction: 1-20
19 20
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21 22
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Access networks: data center networks
§ high-bandwidth links (10s to 100s Gbps) connect hundreds to thousands of servers together, and to Internet
Courtesy: Massachusetts Green High Performance Computing Center (mghpcc.org)
mobile network
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Introduction: 1-21
Host: sends packets of data
host sending function:
§takes application message
§breaks into smaller chunks, known as packets, of length L bits
§transmits packet into access network at transmission rate R
two packets, L bits each
R: link transmission rate = L (bits)
21 • link transmission rate, aka link host
capacity, aka link bandwidth
packet = transmission
delay
time needed to transmit L-bit packet into link
R (bits/sec)
Introduction: 1-22
Links: physical media
§ bit: propagates between transmitter/receiver pairs
§ physical link: what lies between transmitter & receiver
§ guided media:
• signals propagate in solid
media: copper, fiber, coax
§ unguided media:
• signals propagate freely, e.g., radio
Twisted pair (TP)
§ two insulated copper wires
• Category5:100Mbps,1GbpsEthernet • Category6:10GbpsEthernet
Introduction: 1-23
Links: physical media
Coaxial cable:
§ two concentric copper conductors § bidirectional
§ broadband:
• multiplefrequencychannelsoncable • 100’sMbpsperchannel
Fiber optic cable:
§ glass fiber carrying light pulses, each pulse a bit
§ high-speed operation:
• high-speed point-to-point
transmission(10’s-100’sGbps) § low error rate:
• repeaters spaced far apart
• immune to electromagnetic noise
Introduction: 1-24
23 24
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Links: physical media
Wireless radio
§ signal carried in various “bands” in electromagnetic spectrum
§ no physical “wire”
§ broadcast, “half-duplex” (sender to receiver)
§ propagation environment effects:
• reflection
• obstruction by objects • Interference/noise
Radio link types:
§ Wireless LAN (WiFi)
• 10-100’s Mbps; 10’s of meters
§ wide-area (e.g., 4G cellular) • 10’s Mbps over ~10 Km
§ Bluetooth: cable replacement • short distances, limited rates
§terrestrial microwave
• point-to-point; 45 Mbps channels
§ satellite
• up to 45 Mbps per channel • 270 msec end-end delay
Introduction: 1-25
Chapter 1: roadmap
§ What is the Internet?
§ What is a protocol?
§ Network edge: hosts, access network, physical media
§ Network core: packet/circuit switching, internet structure
§ Performance: loss, delay, throughput
§ Security
§ Protocol layers, service models
§ History
Introduction: 1-26
25 26
The network core
§ mesh of interconnected routers
§ packet-switching: hosts break application-layer messages into packets
• network forwards packets from one router to the next, across links on path from source to destination
mobile network
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Introduction: 1-27
Two key network-core functions
routing algorithm
Forwarding:
§aka “switching” §local action:
move arriving packets from router’s input link to appropriate router output link
1 32
Routing:
§ global action: determine source- destination paths taken by packets
§ routing algorithms
Introduction: 1-28
llocall forward header value
0100 0101 0111 1001
diing tablle output link
3 2 2 1
destination address in arriving packet’s header
27 28
7
0111

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routing
Introduction: 1-29
forwarding
forwarding
Introduction: 1-30
29 30
Packet-switching: store-and-forward
L bits
per packet
source 3 2 1 destination R bps R bps
§ packet transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R bps
§storeandforward:entirepacketmust arriveat router before it can be transmitted on next link
One-hop numerical example:
§L = 10 Kbits
§R = 100 Mbps
§ one-hop transmission delay
= 0.1 msec
Introduction: 1-31
Packet-switching: queueing
R=100Mb/s
A
B
R=1.5Mb/s
C
D
E
queue of packets waiting for transmission over output link
Queueing occurs when work arrives faster than it can be serviced:
Introduction: 1-32
31 32
8

Packet-switching: queueing
R=100Mb/s
A
B
R=1.5Mb/s
C
D
E
queue of packets waiting for transmission over output link
Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time:
§packets will queue, waiting to be transmitted on output link §packets can be dropped (lost) if memory (buffer) in router fills up
Introduction: 1-33
Alternative to packet switching: circuit switching
end-end resources allocated to, reserved for “call” between source and destination
§ in diagram, each link has four circuits. • call gets 2nd circuit in top link and 1st
circuit in right link. §dedicated resources: no sharing
• circuit-like (guaranteed) performance § circuit segment idle if not used by call (no
sharing)
§commonly used in traditional telephone networks
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive
Introduction: 1-34
33 34
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Circuit switching: FDM and TDM
Frequency Division Multiplexing (FDM)
§optical, electromagnetic frequencies divided into (narrow) frequency bands
§ each call allocated its own band, can transmit at max rate of that narrow band
Time Division Multiplexing (TDM)
§time divided into slots
§each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band (only) during its time slot(s)
4 users
time
time
Introduction: 1-35
Packet switching versus circuit switching
example:
§ 1 Gb/s link § each user:
• 100 Mb/s when “active” • active 10% of time
N
users
1 Gbps link
Q: how many users can use this network under circuit-switching and packet switching? §circuit-switching: 10 users
§packet switching: with 35 users, probability > 10 active at same time is less than .0004 *
Q: how did we get value 0.0004? A: HW problem (for those with
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive
course in probability only)
Introduction: 1-36
35 36
9
…..
frequency frequency

37 38
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Packet switching versus circuit switching
Is packet switching a “slam dunk winner”?
§ great for “bursty” data – sometimes has data to send, but at other times not • resource sharing
• simpler, no call setup
§ excessive congestion possible: packet delay and loss due to buffer overflow • protocols needed for reliable data transfer, congestion control
§ Q: How to provide circuit-like behavior with packet-switching?
• “It’s complicated.” We’ll study various techniques that try to make packet
switching as “circuit-like” as possible.
Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)?
Introduction: 1-37
Internet structure: a “network of networks”
§ hosts connect to Internet via access Internet Service Providers (ISPs)
§ access ISPs in turn must be interconnected
• so that any two hosts (anywhere!) can send packets to each other
§ resulting network of networks is very complex
• evolution driven by economics, national policies
mobile network
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
Let’s take a stepwise approach to describe current Internet structure
Internet structure: a “network of networks”
Question: given millions of access ISPs, how to connect them together?
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
Introduction: 1-39
Internet structure: a “network of networks”
Question: given millions of access ISPs, how to connect them together?
access net
access net
access net
access net
access net
access net
access net
access net
access net
connecting each access ISP to
access net
access net
each other directly doesn’t scale:
2
O(N ) connections.
access net
access net
access net
access
access net net
Introduction: 1-40
39 40
10
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…

41
42
43
44
Internet structure: a “network of networks”
Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement.
Internet structure: a “network of networks”
But if one global ISP is viable business, there will be competitors ….
access net
access net
access net
access net
access net
access
net access
access access net net
access net
want to be connected
access net
ISP A ISP C
access net
access net
access net
Internet exchange point
access net
access net
access net
ISP B
access net
access net
access net
access net
access net
ISP A ISP C
access net
access net
access net
access net
ISP A ISP C
access net
access net
global ISP
access net
access net
access net
access net
…
…
…
…
access net
access net
peering link
access net
access net
regional ISP
access net
access net
IXP
ISP B
access net
access net
access net
access net
access net
access net
access net
IXP
access net
access net
access net
access net
access net
access net
Internet structure: a “network of networks”
Internet structure: a “network of networks”
But if one global ISP is viable business, there will be competitors …. who will
… and regional networks may arise to connect access nets to ISPs
access net
access net
access net
IXP
access net
IXP
access
net access
access net
access net
access net
access net
ISP B
access net
access net
access net
Introduction: 1-41
Introduction: 1-42
Introduction: 1-43
Introduction: 1-44
net net
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…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
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Internet structure: a “network of networks”
… and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users
access net
access net
access net
access net
access net
access net
access net
ISP A ISP C
access net
IXP
access net
access net
Content provider network
ISP B
IXP
regional ISP
access net
access net
access net
access net
access
access net net
Introduction: 1-45
Internet structure: a “network of networks”
Tier 1 ISP Tier 1 ISP Google
IXP
Regional ISP
access access access access ISP ISP ISP ISP
IXP
Regional ISP
access access access
ISP ISP ISP ISP
IXP
At “center”: small # of well-connected large networks
§ “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage § content provider networks (e.g., Google, Facebook): private network that connects its
data centers to Internet, often bypassing tier-1, regional ISPs
Introduction: 1-46
access
45 46
Chapter 1: roadmap
§ What is the Internet?
§ What is a protocol?
§ Network edge: hosts, access network, physical media
§ Network core: packet/circuit switching, internet structure
§ Performance: loss, delay, throughput
§ Security
§ Protocol layers, service models
§ History
Introduction: 1-47
How do packet delay and loss occur?
§ packets queue in router buffers, waiting for turn for transmission
§ queue length grows when arrival rate to link (temporarily) exceeds output link
capacity
§ packet loss occurs when memory to hold queued packets fills up
packet being transmitted (transmission delay) A
B
packets in buffers (queueing delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
Introduction: 1-48
47 48
12
…
…
…
…
…
…

49
50
51
52
Packet delay: four sources
transmission
A propagation B nodal
dnodal = dproc + dqueue + dtrans + dprop
Packet delay: four sources
processing queueing
nodal
dproc: nodal processing § check bit errors
§ determine output link § typically < microsecs dqueue: queueing delay § time waiting at output link for transmission § depends on congestion level of dtrans: transmission delay: § L: packet length (bits) § R: link transmission rate (bps) § dtrans = L/R dprop: propagation delay: § d: length of physical link § s: propagation speed (~2x108 m/sec) § dprop = d/s Introduction: 1-50 Caravan analogy 100 km ten-car caravan toll booth (aka 10-bit packet) (aka link) § car ~ bit; caravan ~ packet; toll service ~ link transmission § toll booth takes 12 sec to service car (bit transmission time) § “propagate” at 100 km/hr § Q: How long until caravan is lined up before 2nd toll booth? 100 km Caravan analogy ten-car caravan (aka 10-bit packet) 100 km (aka router) 100 km router dtrans and dprop very different toll booth § time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec § time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr) = 1 hr toll booth toll booth § A: 62 minutes § suppose cars now “propagate” at 1000 km/hr § and suppose toll booth now takes one min to service a car § Q: Will cars arrive to 2nd booth before all cars serviced at first booth? A: Yes! after 7 min, first car arrives at second booth; three cars still at first booth Introduction: 1-52 toll booth Introduction: 1-49 Introduction: 1-51 A B transmission propagation processing queueing dnodal = dproc + dqueue + dtrans + dprop 1/5/21 13 1/5/21 Packet queueing delay (revisited) § a: average packet arrival rate § L: packet length (bits) § R: link bandwidth (bit transmission rate) L . a : arrival rate of bits “traffic R service rate of bits intensity” §La/R ~ 0: avg. queueing delay small §La/R -> 1: avg. queueing delay large §La/R > 1: more “work” arriving is
more than can be serviced – average delay infinite!
traffic intensity = La/R 1 La/R ~ 0
La/R -> 1
Introduction: 1-53
“Real” Internet delays and routes
§ what do “real” Internet delay & loss look like?
§ traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:
• sends three packets that will reach router i on path towards destination (with time-to-live field value of i)
• router i will return packets to sender
• sender measures time interval between transmission and reply
3 probes 3 probes
3 probes
Introduction: 1-54
53 54
Real Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr 3 delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
3 delay measurements
to border1-rt-fa5-1-0.gw.umass.edu
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 ***
18 ***
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
* Do some traceroutes from exotic countries at www.traceroute.org
trans-oceanic link looks like delays
decrease! Why?
* means no response (probe lost, router not replying)
Introduction: 1-55
Packet loss
§ queue (aka buffer) preceding link in buffer has finite capacity
§ packet arriving to full queue dropped (aka lost)
§ lost packet may be retransmitted by previous node, by source end system, or not at all
A
B
buffer
(waiting area) packet being transmitted
packet arriving to full buffer is lost
* Check out the Java applet for an interactive animation (on publisher’s website) of queuing and loss
Introduction: 1-56
55 56
14
average queueing delay

Throughput
§ throughput: rate (bits/time unit) at which bits are being sent from sender to receiver
• instantaneous: rate at given point in time • average: rate over longer period of time
plinipkectahpatccitayn carry pilpinekthcapt accaintycarry
server sends bits server, with
R fbluitids/aset crate Rflubiditas/tsreacte sc
(fluid) into pipe file of F bits
(Rs bits/sec)
(Rc bits/sec)
to send to client
Introduction: 1-57
Throughput
Rs < Rc What is average end-end throughput? Rs bits/sec Rs > Rc What is average end-end throughput? Rc bits/sec
bottleneck link
link on end-end path that constrains end-end throughput
Rc bits/sec
Rs bits/sec
Introduction: 1-58
57
58
Throughput: network scenario
Chapter 1: roadmap
§ What is the Internet?
§ What is a protocol?
§ Network edge: hosts, access network, physical media
§ Network core: packet/circuit switching, internet structure
§ Performance: loss, delay, throughput
§ Security
§ Protocol layers, service models
§ History
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Rs
Rs
Rc
Rc
R
Rs
Rc
§ §
per-connection end- end throughput: min(Rc,Rs,R/10)
in practice: Rc or Rs is often bottleneck
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/
59
60
10 connections (fairly) share backbone bottleneck link R bits/sec
Introduction: 1-59
Introduction: 1-60
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Network security
§ Internet not originally designed with (much) security in mind
• original vision: “a group of mutually trusting users attached to a transparent network”J
• Internet protocol designers playing “catch-up”
• security considerations in all layers! §We now need to think about:
• how bad guys can attack computer networks
• how we can defend networks against attacks
• how to design architectures that are immune to attacks
Introduction: 1-61
Network security
§ Internet not originally designed with (much) security in mind
• original vision: “a group of mutually trusting users attached to a transparent network”J
• Internet protocol designers playing “catch-up”
• security considerations in all layers! §We now need to think about:
• how bad guys can attack computer networks
• how we can defend networks against attacks
• how to design architectures that are immune to attacks
Introduction: 1-62
61 62
Bad guys: packet interception
packet “sniffing”:
§broadcast media (shared Ethernet, wireless)
§promiscuous network interface reads/records all packets (e.g.,
including passwords!) passing by
AC
src:B dest:A payload
B
Wireshark software used for our end-of-chapter labs is a (free) packet-sniffer
Introduction: 1-63
Bad guys: fake identity
IP spoofing: injection of packet with false source address
AC
src:B dest:A payload
B
Introduction: 1-64
63 64
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65
66
67
68
Bad guys: denial of service
Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic
Lines of defense:
1. select target
2. break into hosts around the network (see botnet)
3. send packets to target from compromised hosts
hardware assist in traditional Internet
§confidentiality: via encryption
§integrity checks: digital signatures prevent/detect tampering §access restrictions: password-protected VPNs
Chapter 1: roadmap
§ § §
§
§ § § §
What is the Internet? What is a protocol?
Network edge: hosts, access network, physical media
Network core: packet/circuit switching, internet structure Performance: loss, delay, throughput Security
Protocol layers, service models
History
Networks are complex, with many “pieces”:
§hosts
§routers
§links of various media §applications §protocols
§hardware, software
Question: is there any hope of organizing structure of network?
§and/or our discussion of networks?
target
§ firewalls: specialized “middleboxes” in access and core networks:
§ off-by-default: filter incoming packets to restrict senders, receivers, applications
Introduction: 1-65
§detecting/reacting to DOS attacks
… lots more on security (throughout, Chapter 8)
Protocol “layers” and reference models
Introduction: 1-66
Introduction: 1-67
Introduction: 1-68
§ authentication: proving you are who you say you are
• cellular networks provides hardware identity via SIM card; no such
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Example: organization of air travel
end-to-end transfer of person plus baggage
ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing
ticket (complain) baggage (claim) gates (unload) runway landing airplane routing
airplane routing
How would you define/discuss the system of airline travel?
§ a series of steps, involving many services
Introduction: 1-69
Example: organization of air travel
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
ticketing service
baggage service
gate service
runway service
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
aroiruptlianngesreoruvticineg
airplane routing
layers: each layer implements a service §via its own internal-layer actions
§relying on services provided by layer below
Introduction: 1-70
Why layering?
Approach to designing/discussing complex systems:
§ explicit structure allows identification, relationship of system’s pieces
• layered reference model for discussion
§ modularization eases maintenance, updating of system
• change in layer’s service implementation: transparent to rest of system
• e.g., change in gate procedure doesn’t affect rest of system
Introduction: 1-71
Layered Internet protocol stack
§application: supporting network applications • HTTP, IMAP, SMTP, DNS
§transport: process-process data transfer • TCP, UDP
§network: routing of datagrams from source to destination
• IP, routing protocols
§link: data transfer between neighboring network elements
• Ethernet, 802.11 (WiFi), PPP §physical: bits “on the wire”
application
ttrranssporrtt
network
link
physical
Introduction: 1-72
71 72
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Services, Layering and Encapsulation
application
transport
network
link
physical
M
Application exchanges messages to implement some application service using services of transport layer
Ht M
Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer
§ transport-layer protocol encapsulates application-layer message, M, with transport layer-layer header Ht to create a transport-layer segment
• Ht used by transport layer protocol to implement its service
source
destination
Introduction: 1-73
application
transport
network
link
physical
Services, Layering and Encapsulation
application
transport
network
link
physical
application
transport
network
link
physical
source
M
Ht M
Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer
HnHt M
Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services
§ network-layer protocol encapsulates transport-layer segment [Ht | M] with network layer-layer header Hn to create a network-layer datagram
• Hn used by network layer protocol to destination implement its service
Introduction: 1-74
73 74
Services, Layering and Encapsulation
application
transport
network
link
physical
application
transport
network
link
physical
source
M
Ht M
HnHt M
Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services
Hl Hn Ht M
Link-layer protocol transfers datagram [Hn| [Ht |M] from host to neighboring host, using network-layer services
§ link-layer protocol encapsulates network datagram [Hn| [Ht |M], with link-layer header Hl to create a link-layer frame
destination
Introduction: 1-75
Services, Layering and Encapsulation
application
transport
network
link
physical
application
transport
network
link
physical
message segment datagram frame
M
Ht M
Hn Ht M Hl Hn Ht M
M Ht M Hn Ht M HlHnHt M
source
destination
Introduction: 1-76
75 76
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source
Encapsulation: an end-end view
application
transport
network
link
physical
message M segment Ht M datagram Hn Ht M frame Hl Hn Ht M
link
physical
destination
Hn Ht M HlHnHt M
switch
Ht M
router
network
Hn
link physical
application
transport
network
link
physical
M Ht M HnHt M Hl Hn Ht M
Introduction: 1-77
Chapter 1: roadmap
§ What is the Internet?
§ What is a protocol?
§ Network edge: hosts, access network, physical media
§ Network core: packet/circuit switching, internet structure
§ Performance: loss, delay, throughput
§ Security
§ Protocol layers, service models
§ History
Introduction: 1-78
Internet history
1961-1972: Early packet-switching principles
§ 1961: Kleinrock – queueing theory shows effectiveness of packet-switching
§ 1964: Baran – packet-switching in military nets
§ 1967: ARPAnet conceived by Advanced Research Projects Agency
§ 1969: first ARPAnet node operational
§ 1972:
• ARPAnet public demo
• NCP (Network Control Protocol)
first host-host protocol • first e-mail program
• ARPAnet has 15 nodes
Internet history
1972-1980: Internetworking, new and proprietary networks
§1970: ALOHAnet satellite network in Hawaii
§1974: Cerf and Kahn – architecture for interconnecting networks
§1976: Ethernet at Xerox PARC §late70’s: proprietary
architectures: DECnet, SNA, XNA §1979: ARPAnet has 200 nodes
Cerf and Kahn’s internetworking principles:
§ minimalism, autonomy – no internal changes required to interconnect networks
§ best-effort service model
§ stateless routing
§ decentralized control
define today’s Internet architecture
Introduction: 1-80
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Internet history
1980-1990: new protocols, a proliferation of networks
§ 1983: deployment of TCP/IP
§ 1982: smtp e-mail protocol
defined
§ 1983: DNS defined for name- to-IP-address translation
§ 1985: ftp protocol defined
§ 1988: TCP congestion control
§ new national networks: CSnet, BITnet, NSFnet, Minitel
§ 100,000 hosts connected to confederation of networks
Introduction: 1-81
Internet history
1990, 2000s: commercialization, the Web, new applications
§ early 1990s: ARPAnet decommissioned
§ 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
§ early 1990s: Web
• hypertext [Bush 1945, Nelson 1960’s] • HTML, HTTP: Berners-Lee
• 1994: Mosaic, later Netscape
• late 1990s: commercialization of the Web
late 1990s – 2000s:
§more killer apps: instant messaging, P2P file sharing
§network security to forefront §est. 50 million host, 100 million+
users
§backbone links running at Gbps
Introduction: 1-82
Internet history
2005-present: scale, SDN, mobility, cloud
§ aggressive deployment of broadband home access (10-100’s Mbps)
§ 2008: software-defined networking (SDN)
§ increasing ubiquity of high-speed wireless access: 4G/5G, WiFi
§ service providers (Google, FB, Microsoft) create their own networks
• bypass commercial Internet to connect “close” to end user, providing “instantaneous” access to social media, search, video content, …
§ enterprises run their services in “cloud” (e.g., Amazon Web Services, Microsoft Azure)
§ rise of smartphones: more mobile than fixed devices on Internet (2017)
§ ~18B devices attached to Internet (2017)
Introduction: 1-83
Chapter 1: summary
We’ve covered a “ton” of material!
§ Internet overview
§ what’s a protocol?
§ network edge, access network, core
• packet-switching versus circuit- switching
• Internet structure
§ performance: loss, delay, throughput
§ layering, service models
§ security
§ history
You now have:
§ context, overview, vocabulary, “feel” of networking
§ more depth, detail, and fun to follow!
Introduction: 1-84
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Additional Chapter 1 slides
Introduction: 1-85
ISO/OSI reference model
Two layers not found in Internet protocol stack!
§ presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
§ session: synchronization, checkpointing, recovery of data exchange
§ Internet stack “missing” these layers! • these services, if needed, must be
implemented in application • needed?
The seven layer OSI/ISO reference model
application
presentation
session
transport
network
link
physical
Introduction: 1-86
85 86
Wireshark
packet analyzer
packet capture (pcap)
application (www browser, email client)
Transport (TCP/UDP)
Network (IP)
application
OS
copy of all
Ethernet frames sent/received
Link (Ethernet)
Physical
Introduction: 1-87
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22