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Transcript of IP and Networking Basic
8/7/2019 IP and Networking Basic
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Appendix 1
IP and Networking Basics
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Introduction Standalone computers.
Computers in a network.
Different applications/servicesbetween computers: e-mail, FileTransfer, Remote Login, Web
Surfing, Network Management,chatting, playing games etc.
Appendix 2
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Appendix 3
Packet Switched Network Usual telephone network is circuit switched
o For each call, a dedicated circuit is establishedo Dedicated bandwidth
Modern data networks are packet switchedo Data is chopped up into discrete packetso Packets are transmitted independentlyo No real circuit is established
o More efficient bandwidth usageo But more complex than circuit switched
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Appendix 4
Network Protocols
Study of networking focused on protocols Networking protocols precisely specify the
communication rules Details are given in RFCs
o RFC is effectively an Internet standard
Stateless protocols don·t remember Stateful protocols do remember
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To achieve interworking betweencomputers & other devices likeservers, routers etc the computer ismade to work in a hierarchical mannerie it is to work as a layered model.Each layer doing certainfunctionalities & offering services to
its upper layer.
Appendix 5
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6
International Standard Organisation (ISO) devised a7 layered model called Open System Interconnection(OSI model)
OSI Model
OSI Model
PHYSICAL
DATA LINK
NETWORK
TRANSPORT
SESSION
PRESENTATION
APPLICATION
PHYSICAL
DATA LINK
NETWORK
TRANSPORT
SESSION
PRESENTATION
APPLICATION
A B
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Each computer has this OSI model
embedded in it. Whenever any computer wants to
communicate with any other computer
or entity it will adopt a set of rulesagreeable to all the computers &entities in the network. This set ofrules is called Protocol. Each layer
communicates with its peer layer usinga protocol before actual data transfertakes place.
Appendix7
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So we require a stack of protocolcalled Protocol Suite to effectcommunication between computers ina network.
Different protocol suites areavailable like:
(a) AppleTalk (d) TCP/IP
(b) OSI (e) DECnet(c) IPX/SPX (f) XNS
Appendix8
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Appendix9
IP Protocols Internet or IP technology over the years hasemerged as the most prominent datacommunication technology.
TCP/IP protocol has become de-facto datacomm standard throughout the world.
It can carry even voice/video also over IPprotocol and in turn has started challengingthe complete monopoly of TDM technology invoice communication.
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Appendix10
TCP/IP and OSI OSI is made of seven layers.
TCP/IP protocol is made of five layers.
PHYSICAL
DATA LINK
NETWORK
TRANSPORT
APPLICATION
PHYSICAL
DATA LINK
NETWORK
TRANSPORT
SESSION
PRESENTATION
APPLICATION
OSI Model TCP/IP Model
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Appendix11
TCP/IP Protocol Suite
D
N
T
A
ICMP IGMPRARPARP
FTPSMTP
TELNETHTTP
TFTPNFS
SNMPDNS
TCP UDP
IP
Protocols defined by the underlying networks
P
Ethernet, Token Ring, FDDI, HDLC,FR, PPP, ATM
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Appendix12
Network Includes
o Computers
oServerso Routers
o Wireless devices
o Etc.
Purpose is totransmit data
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Appendix13
Network Edge
Network edgeincludes
Hostso Computerso Laptopso Servers
o Cell phoneso Etc., etc.
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Appendix14
Network Core
Network coreconsists ofo Interconnected
mesh of routers
Purpose is tomove data fromhost to host
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Appendix15
Layering in Action
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
data data
At source, data goes down the protocol stack Each router processes packet up to network layer
o That·s where routing info lives Router then passes packet down the protocol stack Destination processes up to application layer
o That·s where the data lives
hosthost
router
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Appendix16
Encapsulation X = application data at the source
As X goes down protocol stack, eachlayer adds header information:o Application layer: (H, X)
o Transport layer: (H, (H, X))
o Network layer: (H, (H, (H, X)))
o Link layer: (H, (H, (H, (H, X))))
Header has info required by layer Note that app header is on the inside
application
tr ansport
network
link
physical
data X
packet
(H,(H,(H,(H,X))))
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Appendix17
Application Layer Applications
o Web browsing, email, P2P, etc.o Run on hostso Hosts want network to be transparent
Application layer protocolso HTTP, SMTP, IMAP, Gnutella, etc., etc.
Protocol is one part of an applicationo For example, HTTP only part of Web browsing
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Appendix18
Client-Server Model Client ´speaks firstµ
Server tries to respond to request
Hosts are clients and/or servers
Example: Web browsingo You are the client (request web page)
o Web server is the server
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Appendix19
Peer-to-Peer (P2P) Model Hosts act as clients and servers For example, when sharing music
o You are client when requesting a fileo You are a server when someone downloads a filefrom you
In P2P model, more difficult for client tofind a server
Many different P2P models
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Appendix20
HTTP Example
HTTP --- HyperText Transfer Protocol Client (you) request a web page Server responds to your request
HTTP request
HTTP response
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Appendix21
Web Cookies
HTTP is stateless --- cookies used to add state Initially, cookie sent from server to browser Browser manages cookie, sends it to server Server looks in cookie database to ´rememberµ you
initialsession
any latersession
cookie
cookie
Cookiedatabase
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Appendix22
Web Cookies Web cookies can be used for
o Shopping carts
o Recommendations, etc.o A weak form of authentication
Privacy concernso Web site can learn a lot about youo Multiple web sites could learn even more
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Appendix23
SMTP SMTP used to send email from sender to
recipient·s mail server Then use POP3, IMAP or HTTP (Web mail)
to get messages from server As with many application protocols, SMTP
commands are human readable
SMTPPOP3
Sender RecipientSMTP
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Appendix24
Application Layer DNS --- Domain Name Service
o Convert human-friendly names such aswww.google.com into 32-bit IP address
o A distributed hierarchical database
Only 13 ´rootµ DNS servers worldwide
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Appendix25
Transport Layer The network layer offers unreliable, ´best
effortµ delivery of packets Any improved service must be provided by
the hosts Transport layer has two protocols
o TCP � better service, more overheado UDP � minimal service, minimal overhead
TCP and UDP run on hosts, not routers
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Appendix26
TCP
TCP assures that packetso Arrive at destinationo Are processed in ordero Are not sent too fast for receiver (flow control)
TCP also provideso Network-wide congestion control
TCP is ´connection-orientedµo TCP contacts server before sending datao Orderly setup and take down of ´connectionµo But no true connection, only a logical connection
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Appendix27
TCP Header
Source and destination port Sequence number Flags (ACK, SYN, RST, etc.) 20 bytes (if no options)
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Appendix28
TCP Three Way Handshake
SYN: synchronization requested SYN-ACK: acknowledge SYN request
ACK: acknowledge msg 2 and send data Then TCP ´connectionµ established
o Connection terminated by FIN or RST packet
SYN request
SYN-ACK
ACK (and data)
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Appendix29
Denial of Service Attack The TCP 3-way handshake makes denial of
service (DoS) attacks possible
Whenever SYN packet is received, servermust remember ´half-openµ connectiono Remembering consumes resources
o Too many half-open connections and server
resources will be exhaustedo Then server can·t respond to new connections
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Appendix 30
UDP UDP is minimalist, ´no frillsµ service
o No assurance that packets arriveo No assurance packets are in order, etc., etc.
Why does UDP exist?o More efficient (smaller header)o No flow control to slow down sendero No congestion control to slow down sender
Packets sent too fast, they will be droppedo Either at intermediate router or at destinationo But in some apps this is OK (audio/video)
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Appendix 31
Network Layer Core of network/Internet
o Interconnected mesh of routers
Purpose of network layer
o Route packets through this mesh Network layer protocol is IPo Follows a ´best effortµ approach
IP runs in every host and every router Routers also run routing protocols
o Used to determine the path to send packetso Routing protocols: RIP, OSPF, BGP, etc.
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Appendix 32
IP Addresses
IP address is 32 bits
Every host has an IP address
Not enough IP addresses!
o Lots of tricks to extend address space IP addresses given in dotted decimal notation
o For example: 195.72.180.27
o Each number is between 0 and 255
Host·s IP address can change
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Appendix 33
Socket
Each host has a 32 bit IP address But many processes on one host
o You can browse web, send email at same time
How to distinguish processes on a host? Each process has a 16 bit port number
o Port numbers < 1024 are ´well-knownµ ports(HTTP port 80, POP3 port 110, etc.)
o Port numbers above 1024 are dynamic (as needed)
IP address and port number define a socketo Socket uniquely identifies a process
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Appendix 34
IP Header
IP header used by routers
o Note source and destination IP addresses Time to live (TTL) limits number of ´hopsµ
o So packets can·t circulate forever
Fragmentation information (see next slide)
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Appendix 35
IP Fragmentation
Each link limits maximum size of packets
If packet is too big, router fragments it Re-assembly occurs at destination
re-assembled
fragmented
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Appendix 36
IP Fragmentation One packet becomes multiple packets Packets reassembled at destination
o Prevents multiple fragmentation/re-assemble
Fragmentation is a security issue!o Fragments may obscure real purpose of packeto ´Fragmentsµ can overlap when re-assembledo Must re-assemble packet to fully understand ito Lots of work for firewalls, for example
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Appendix 37
IPv6
Current version of IP is IPv4
IPv6 is a new-and-improved version
IPv6 provideso Longer addresses: 128 bits
o Real security ´built-inµ (IPSec)
But difficult to migrate from v4 to v6
So IPv6 has not taken hold yet
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Appendix 38
Link Layer Link layer sends
packet from onenode to next
Each link can bedifferento Wiredo Wireless
o Etherneto Point-to-point«
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Appendix 39
Link Layer Implemented in adapter known as
network interface card (NIC)
o Ethernet cardo Wireless 802.11 card, etc.
NIC is (mostly) out of host·s control
o Implements both link and physical layers
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Appendix 40
Ethernet
Ethernet is a multiple access protocol Many hosts access a shared media
o On a local area network, or LAN
In ethernet, two packets can collideo Then data is corruptedo Packets must be resento How to be efficient in distributed environment?
o Many possibilities, ethernet is most popular We won·t discuss details here
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Appendix 41
Link Layer Addressing
IP addresses live at network layer Link layer also requires addresses
o MAC address (LAN address, physical address)
MAC addresso 48 bits, globally uniqueo Used to forward packets over one link
Analogy
o IP address is like home addresso MAC address is like social security number
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Appendix 42
ARP Address resolution protocol, ARP Used at link layer to find MAC address of
given IP address Each host has ARP table
o Generated automaticallyo Entries expire after some time (20 min)o ARP used to find ARP table entrieso ARP table also known as ARP cache
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Appendix 43
ARP
ARP is stateless ARP sends request and receives ARP reply Replies used to fill ARP cache
IP: 111.111.111.001 IP: 111.111.111.002
MAC: AA-AA-AA-AA-AA-AA MAC: BB-BB-BB-BB-BB-BB
111.111.111.002BB-BB-BB-BB-BB-
BB111.111.111.001
AA-AA-AA-AA-AA-
AAARP cache ARP cache
LAN
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THANKS
Appendix 44