essentials of the internet protocol and tcp/ip architecture

2008/2009

Essentials of the Internet Protocoland TCP/IP Architecture

Prepared by:Ignac Lovrek, Maja Matijašević, Gordan Gledec, Gordan Ježić, Josip Gracin, Domagoj Mikac, Ognjen Dobrijević, Vedran Podobnik

University of ZagrebFaculty of Electrical Engineering and ComputingDepartment of Telecommunications

2008/2009

Introduction

History and size of the InternetInternet hierarchyStandards organizationsRequest for Comments series

Size of the Internet

University of Zagreb, FER SIF 2744, 2008/2009 3 of 48

Internet hierarchy

LANcorporate network

SIF 2744, 2008/2009University of Zagreb, FER 4 of 48

Tier 1

Home userphone, ISDN,xDSL, cable

ISP

ISP

IXP

ISP ISPISP

IXP

POP POP

ISPISP

POP

POPPOP

IXPPOP

ISP

direct peeringISP Legend:

ISP - Internet Service ProviderIXP - Internet Exchange PointPOP - Internet Point of Presence

Tier 2

Tier 3

Internet standards organizations

Internet ArchitectureBoard IAB

Internet EngineeringTask Force IETF

Internet EngineeringSteering Group IESG

Internet ResearchTask Force IRTF

Internet ResearchSteering Group IRSG

RFC Editor

Internet Corporation for AssignedNames and Numbers ICANN(Internet Assigned Numbers

Authority IANA is now under ICANN)

World Wide WebConsortium W3C

InternationalTelecommunication

Union ITU

Internet SocietyISOC

3rd GenerationPartnership Project

3GPPIP address space allocation- 5 Regional Internet Registries (RIRs); RIPE NCC for EuropeProtocol identifier assignmentDomain name system management

EuropeanTelecommunications

Standards Institute ETSI

standardizationThe amount of standardization within the Internet is the minimum necessary for

effective interworking.

administration collaboration


Requests for Comment (RFC) series

♦ RFC documents are a series of memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies

♦ RFC Editor (team) edits and publishes RFCs onlineRFC Index http://www.rfc-editor.org/rfc-index.html

RFC Editor issues each RFC document with a unique serial numberonce published, RFCs never change – errata are published separatelyRFC subseries

Internet Standard (STD), For Your Information (FYI), Best Current Practice (BCP)

also important: RFC status – may be “standards track” (proposed standard, draft standard, Internet standard), or other (informational, experimental, BCP, or historic)

♦ the IETF adopts some of the proposals published in RFCs as Internet standards - not all RFCs are/become Internet standards; only ~70 STDs out of 5300+ (as of Nov. 2008) RFCs


2008/2009

Structure of the Internet

Logical and physical viewAutonomous System

Logical vs. physical view

Legend: SN – subnet


logical view -one global network

physical view -network of networks

Internet

Autonomous system

♦ Autonomous system (AS)collection of IP networks and routers under the control of one entity (or sometimes more) that presents a common routing policy to the Internet

♦ a unique AS number (ASN) is assigned by IANAfor example, AS2108 CARNET-AS Croatian Academic and Research Network

routing view -collection of ASs

Legend: SN - subnetAS – autonomous system


2008/2009

Protocol stack and the role of TCP/IP

Reference networking modelComparison of OSI and Internet TCP/IP modelTCP/IP functionality

Reference Networking Model

♦ provides an abstract view of network architecture

♦ concept of layeringeach layer implements a set of well-defined functionalitieseach layer provides the foundation and the services required by the layer aboveeach layer-n entity interacts directly only with the layer immediately beneath it, and provides facilities for use by the layer above it

♦ protocol suite = collection of protocols organized into layersprotocol is a “language” that enables an entity in one host to interact with a cooresponding entity (peer) at the same layer in a remote hoststandardized interfaces


Comparison between OSI and TCP/IP architecture

Open Systems Interconnection

Link layer

Network layer

Transport layer

Application layer

TCP/IP (Internet)

Data Link layer

Physical layer

Application layer

Presentation layer

Network layer

Transport layer

Session layer

Application layer

Network layer

Transport layer

Presentation layer

Session layer

Link layer

Network layer

Transport layer

Application layer

Physical layer

Data Link layer

(Physical layer)


TCP/IP protocol stack

Link layer

Network layer

Transport layer

Application layer

IP routing(RIP, OSPF, BGP)

control (ICMP, IGMP) AR

P

RARP

TCP UDPFT

PTe

lnet

DNS

SMTP

HTTP

TFTP

SNMP

RTP

IP - Internet ProtocolICMP - Internet Control Message ProtocolARP - Address Resolution ProtocolRARP - Reverse Address Resolution ProtocolTCP - Transmission Control ProtocolUDP - User Datagram ProtocolFTP - File Transfer Protocol

SMTP - Simple Mail Transfer ProtocolHTTP - HyperText Transfer ProtocolDNS - Domain Name SystemTFTP - Trivial File Transfer ProtocolSNMP - Simple Network Management ProtocolRTP - Real-time Transport Protocol

Ethernet/IEEE802.x, PPP, ATM, ...

WWW


How TCP/IP works – encapsulation example

data

dataHTTP

dataHTTP

TCP

dataHTTPTCPIP

F

dataHTTP dataTCP

TCPIP

TCPIPF

data

data20 byte 20 byte

46-1500 byte 4 byte14 byte

Transport layer

Network layer

Link layer

Application layer(web appl.)

dataHTTPTCPIP

(Ethernet/IEEE802.3)


2008/2009

Network Layer functionality

Internet Protocol – IPv4Control ProtocolsRouting Protocols

Network layer functionality

♦ connectionless transfer of datagrams → unreliable service♦ each datagram is being independently routed based on IP destination address♦ “best effort” service

Example:♦ node A sends to B: ♦ datagrams may traverse different paths and arrive in a different order, e.g. :

1 2 3

1 23

22

123

12

32

2

2 2

3

3 3

3

3

33

1

1 1

11

A B

3

2

1


2008/2009

Internet Protocol v4

IP featuresDatagram formatFragmentation and reassemblyIP addressing and naming

Internet Protocol

♦ IP, version 4♦ connectionless unreliable transfer of datagrams♦ specified in RFC 791, STD-5♦ defines the Internet addressing scheme

unique address spaceeach host has one unique IP addresses per interfacea host may also use other special addresses (e.g. localhost, multicast, broadcast ,…)if source and destination are located in different networks, IP datagrams are routed through one or more IP routers

♦ defines how to handle fragmentationa datagram must fit in the frame of specific lower layer protocoldatagram bigger than the frame must be fragmentedreceiving side reassembles the fragments


IP datagram format

header,20 octets

max. 60 octets

dataTCPIPF

version Type of Service Total LengthHdr. LenIdentification Fragment Offset

Protocol Header ChecksumTime to LiveSource IP address

Destination IP addressOptions Padding

Higher layer data

Flags

32 bits


IP datagram size - fragmentation and reassembly

♦ datagram must be small enough to fit into the frame of the lower layer protocol

MTU - Maximum Transmission Unitmedia dependentfor example, Ethernet/IEEE 802.3: 1500 bytes

♦ otherwise, the datagram must be split or fragmented into several datagrams

♦ fragments are sent independently and reassembled into the original message at the destination

MTU=1500 MTU=576

fragmentation reassembly

MTU=1500source destination


2008/2009

IP addressing and naming

IP address structureTypes of IP addressesDomain Name SystemAddress Resolution Protocol Internet Control Message Protocol

IP addressing

♦ IP address provides unique identification of the network interfacea device can have more than one interfacedifferent from the physical (MAC) addresses

♦ IP address is required to ensure that the IP datagram is delivered to the correct recipient

♦ Address representation32 bit binary number

hard to read and remember

10100001 00110101 00010011 11001001

161 53 19 201. . .Dotted-decimal notation

easier to rememberSymbolic address or name (hosts.txt)


IP address structure

♦ IP address has two parts:Network Identifier (Net ID)

a certain number of bits (starting from the left-most bit), used to identify the network where the network interface is locatednetwork prefix

Host Identifier (Host ID)the remainder of the bits used to identify the network interface in the network specified with Net ID

♦ type of IP addressunicast, broadcast, multicast

10100001 00110101 00010011 11001001

161 53 19 201. . .

Net ID Host ID


Classes of IP adresses

Class A: 0.0.0.0 - 127.255.255.2550 Net ID Host IDClass B: 128.0.0.0 - 191.255.255.2551 0 Net ID Host IDClass C: 192.0.0.0 - 223.255.255.2551 1 0 Net ID Host IDClass D: 224.0.0.0 - 239.255.255.2551 1 1 0 multicastClass E: 240.0.0.0 - 247.255.255.2551 1 1 1 0 reserved

Number of possible networks

Number of hosts per network

Class A 27-2 = 126 224-2 = 16,277,214

Class B 214 = 16,384 216-2 = 65,534

Class C 221 = 2,097,152 28-2 = 254


Classless addressing scheme

♦ prefix-based representation of IP address♦ partitioning between the NetID and HostID can occur at any

bit boundary in the address♦ length of Net ID is specified with the network prefix following the IP

address

11000011.00011000.00000000.00000000

195.24.0.0/13

network prefix

♦ introduced for the purposes of Classless Inter-Domain Routing (CIDR)network part (NetID) of the IP address is not determined by address classeliminates the significance of address classes for route aggregation(that’s why CIDR is termed classless)


Types of IP addresses

Public address space♦ for use in public Internet♦ IP address must be globally unique

♦ two devices connected to the public Internet cannot have the same IP address

♦ routing must be possible ♦ IANA, ICANN, RIPE...

Private address space♦ for use in private internets♦ organization manages the entire private address space♦ IP addresses within the private network must be unique♦ blocks of IP address space for private internets specified

by IANA: 10/8, 172.16/12, 192.168/16

IP Network Address Translator (NAT)

Reserved address space♦ “this” network 0.0.0.0/8♦ loopback 127.0.0.0/8♦ multicast 224.0.0.0/4♦ broadcast - Host ID all 1s ♦ blocks reserved by IANA, some

subject to allocation, some not

IPv4 Address Space(RFC 3330)


The role of NAT – example

B: 161.53.19.201

NAT

private Internet(address space 10/8)

A: 10.0.0.1

NAT binding:10.0.0.1 ↔ 139.130.1.1

source: 10.0.0.1destination: 161.53.19.201 source: 139.130.1.1

destination: 161.53.19.201

source: 161.53.19.201destination: 139.130.1.1

source: 161.53.19.201destination: 10.0.0.1

public Internet

datagram A->B

datagram B->A

X: 139.130.1.1(public IP address space )


Obtaining an IP address

♦ static address assignmentIP address is manually configured for a network device (i.e. IP phone)acceptable for small networks, complicated for large networksusually applied for network servers, routers and other devices that never change their IP addresses

♦ dynamic address assignmentIP address and other network settings received from a serversimplifies address assignment in large networks (e.g. corporation, ISP)DHCP – Dynamic Host Configuration Protocol (RFC 2131)

successor to BOOTP – Bootstrap ProtocolDHCP server leases an IP address from a previously configured address range to a device for a specific time (allows serial reassignment of IP address)DHCP server provides entire TCP/IP configuration (IP address, subnet mask, default gateway)


Domain Name System (DNS)

♦ numerical IP adresses are hard to remember – a name may be assigned for easier reference

♦ Domain Name System“(...) the idea of a hierarchical name space, with the hierarchy roughly corresponding to organizational structure, and names using ‘.’ as the character to mark the boundary between hierarchy levels.” (RFC 1034)a “directory service” for the Internetdomain – a group of computers most commonly associated by the organization they belong to

top level domain (generic, country)subdomains, for example: .hr, fer.hr, tel.fer.hr

Fully Qualified Domain Name uniquely identifies the host on the Internetfor example, www.tel.fer.hr

maintained as the hierarchical database distributed on the Internetroot DNS server on the top of the hierarchyother DNS servers have authority over their zones/domains


DNS Example


applicationresolver

local DNS server

root DNS128.9.0.107

DNS for .hr161.53.3.7

DNS for .fer.hr161.53.72.21

DNS for tel.fer.hr161.53.19.203

query for www.tel.fer.hr

www.tel.fer.hr?

DNS for .hr

www.tel.fer.hr?

www.tel.fer.hr?

www.tel.fer.hr?

DNS for fer.hr

DNS for tel.fer.hr

161.53.19.221

www.

tel.fe

r.hr?

161.53.19.221

2.

3.

4.

5.

6.1.

hr at fi

fer foi

tel zesoi zpm

.

www oluja

2008/2009

Routing protocols

Classless Interdomain RoutingRouting Information ProtocolOpen Shortest Path FirstBorder Gateway Protocol

IP Routing

♦ Internet is a packet-switching network♦ Classless Inter-Domain Routing – CIDR (RFC 4632)

destination IP address is matched based on NetIDpackets (IP datagrams) are routed independently of each other

♦ no end-to-end connectionhop-by-hop routing

♦ each router contains a routing table which contains its information on the topology of the network

used for matching a destination address to the outgoing network interface entries (i.e. rows) in routing table contain:

destination addressIP address of the next-hop router on the way to the destination

default route – special entry in routing tablematches all destinations – 0.0.0.0/0considered when no other more specific routes are foundused, for example, in leaf networks


Routing Example (1)

`

`

`

175.204.18

196.84.4

175.204.18.2

175.204.18.1

196.84.7.1

196.84.7.3

196.84.4.12

196.84.4.1

196.84.7

Network dest. Network mask Gateway Interface

196.84.4.0 255.255.255.0 196.84.4.12 196.84.4.12

default/0.0.0.0 0.0.0.0 196.84.4.1 196.84.4.12


196.84.7.0 255.255.255.0 196.84.7.3 196.84.7.3

196.84.4.0 255.255.255.0 196.84.4.1 196.84.4.1

default/0.0.0.0 0.0.0.0 196.84.7.1 196.84.7.3


196.84.7.0 255.255.255.0 196.84.7.1 196.84.7.1

196.84.4.0 255.255.255.0 196.84.7.3 196.84.7.1

175.204.18.0 255.255.255.0 175.204.18.2 175.204.18.2

default/0.0.0.0 0.0.0.0 175.204.18.1 175.204.18.2

196.84.7.0

destination196.84.7.56

196.84.7.0


Routing Example (2)Network dest. Network mask Gateway Interface

196.84.4.0 255.255.255.0 196.84.4.12 196.84.4.12

default/0.0.0.0 0.0.0.0 196.84.4.1 196.84.4.12


196.84.7.0 255.255.255.0 196.84.7.3 196.84.7.3

196.84.4.0 255.255.255.0 196.84.4.1 196.84.4.1

default/0.0.0.0 0.0.0.0 196.84.7.1 196.84.7.3


196.84.7.0 255.255.255.0 196.84.7.1 196.84.7.1

196.84.4.0 255.255.255.0 196.84.7.3 196.84.7.1

175.204.18.0 255.255.255.0 175.204.18.2 175.204.18.2

default/0.0.0.0 0.0.0.0 175.204.18.1 175.204.18.2

161.68.78.123

161.68.78.0

161.68.78.0

161.68.78.0

`

`

`

175.204.18

196.84.4

175.204.18.2

175.204.18.1

196.84.7.1

196.84.7.3

196.84.4.12

196.84.4.1

196.84.7

destination


Routing Protocols Classification

EGPEGPExterior Gateway ProtocolBorder Gateway Protocol – BGP ◄Exterior Gateway Protocol - EGP


IGPIGPInterior Gateway Protocol

Open Shortest Path First - OSPF◄Routing Information Protocol – RIP ◄

Interior Gateway Routing Protocol - IGRPIntermediate System to Intermediate System (IS-IS)

AS – Autonomous System

AS2

AS3

EGP

IGP

IGPIGP

AS1

2008/2009

Transport Layer

Transport layer functionalityUser Datagram ProtocolTransmission Control Protocol

Transport Layer functionality

♦ enables communication between processesflow multiplexing, i.e. differentiating between data flows belonging to different processes on the same hosttransport layer address is called porttransport layer API (“socket” API)


Transport Layer Protocols in the Internet: TCP and UDP

User Datagram Protocolconnectionless protocolunreliable transferorder not guaranteedno flow controlno congestion controlapplications:

audio, video, internet telephony, teleconferencing (RTP)dynamic address allocation (BOOTP, DHCP)

Transmission Control Protocolconnection-oriented protocolreliable transferordered deliveryflow controlcongestion controlapplications:

web (HTTP)e-mail (SMTP, POP, IMAP)file transfer (FTP)remote terminal (TELNET)

TCP UDP


Transmission Control Protocol (TCP)

♦ specified in RFC 793♦ functionality of TCP

accepts higher layer data, divides the octet stream into segments, and passes them down to the IP layerprovides ordered, reliable delivery of stream of octetsprovides transport layer addressing/multiplexing (ports)

dataTCPIPF

header,20 octets

max. 60 octets

source portsequence number

acknowledgment numberlength

TCP options (optional) padding

higher layer data

destination port

control bits window sizersvd.checksum urgency pointer

TCP segment structure

32 bits


TCP mechanisms

♦ three phases of a connection: connection establishment, data transfer, connection termination

♦ ordered, reliable data delivery over IPdelivers data as a stream of octetsdivides the octet stream into appropriately sized segments Maximum Segment Size (MSS) is determined by the link-layer frame sizeeach segments is numbered

♦ reliability mechanismsacknowledgmentsretransmission

♦ sliding window flow control♦ congestion avoidance

slow start, fast retransmit and fast recovery algorithmsdoing congestion avoidance in TCP is an important design decision of the Internet network


2008/2009

Putting it all together... how an application uses TCP/IP

World Wide Web example

How WWW works, general idea

IP www.fer.hr ?

www.fer.hr161.53.72.111

161.53.72.111browserbrowser

local DNS server

web serverweb

server

Go to:http://www.fer.hr/


diskHTTP request for root index documentHTTP server responds with HTML source

Example: FER Home page

image

form

active element

- menu

text

(css)


Processing of the source HTML code

♦ in this example, HTML code contains references to:CSS layout imagesJavascripttexttext control elements (formatting, hyperlinks, etc.)

♦ all page elements are fetched from the server by using HTTPthe client may start a new HTTP connection, or use the existing one to get the files from the server

<link href="/_themes/metallish/platinum/style.css" rel="stylesheet" type="text/css">

<img src="/shared/images/spacer.gif" height="6" width="1" alt="">

<script type="text/javascript" src="/lib/v1treeview.js"></script>

<p>Svečana promocija pristupnika koji su diplomirali u veljači i ožujku...<p>

<a title="Pročitaj obavijest" href="/?@=1dhtp#news_8980">Više...</a>


Client application requests the image element…

♦ image on the home page must be fetched from the server (HTTP request)

the size of the image file is 16,711 bytes

♦ to be transported over TCP, the image file must be broken into smaller pieces (<=MSS)

transport layer breaks initial 17 kB into 12 TCP segmentsMSS = MTU - size of {IP, TCP} headers = 1500 – 20 – 20 = 1460 byteseach segment is sent to network layer and routed independently


The server application generates the HTTP response…


HTTP

dataHTTPTCPIP

F

dataHTTP

Application layer(HTTP response)

TCP

IP

EthernetdataHTTPTCPIP

MSS MSS MSS *

TCP

... image data ...

... containing the image being delivered to the client ...

Ethernet

dataHTTP TCPTCP

dataHTTPTCPIP IP

F dataHTTPTCPIP

…………….HTTPApplication layer(HTTP response)

... image data ...


... the client collect all elements and displays the Web page.


essentials of the internet protocol and tcp/ip architecture

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