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Organizing the InternetOrganizing the Internet

Chapter 9

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Knowledge CheckpointsKnowledge Checkpoints

Internet protocols Routing and protocols Internet addressing Organization of the Internet How ISPs work

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Terms to RememberTerms to Remember

TCP/IP suite Packet sequence numbers Port numbers UDP, ICMP,IGMP ARP, RARP RIP, OSPF, IGP, EGP, BGP ARIN, RIPE,APNIC,ICANN CIDR NSP ASP

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TCP/IPTCP/IP Transmission Control Protocol / Internet

Protocol Oldest networking standard (DoD, 1974) Most popular network protocol (70%) Small packet size TCP/IP allows reasonable efficient and error-

free transmission Combination of two protocols

TCP - Transmission Control Protocol IP - Internet Protocol

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Internet ProtocolsInternet Protocols

TCP/IP (suite) Provides layer 4 functionality TCP divides data into packets with a sequence number Assigned to a port (range 1-65,535) Ports identify applications on servers Ports identified by incoming and outgoing IP handles packet forwarding and transport of datagrams

across a network Defines the basic unit of data Functions at Layer 3 Provides host addressing, error notification, fragmentation,

reassembly, routing, and packet time-out

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Internet ProtocolsInternet Protocols

UDP Layer 4 Operates over IP End-to-end connectionless, unreliable datagram service Used for query based applications, multicasting and VoIP

ICMP Provides error-handling Messages related to network management

IGMP Layer 3 Allows Internet hosts to participate in multi-casting

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TCP/IPTCP/IP TCP performs the packetizing function

Breaking data into smaller packets Numbering packets Ensuring reliable delivery of packets Ordering packets at the destination

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TCP/IPTCP/IP

IP performs network routing and addressing functions IPv4 - 32-bit address - 192-bit header IPv6 - 128-bit address - 320-bit header

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Requirements for TCP/IPRequirements for TCP/IP

This information should either come from an internal configuration file or a bootp or DHCP server IP address Subnet mask IP address of DNS server IP address of router, gateway or switch

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1 2 3 4 5 6 7 8 9 10 11 User Data

1 Source port number 16 bits2 Destination port number 16 bits3 Sequence number 32 bits4 ACK number 32 bits5 Header length 4 bits6 Unused 6 bits7 Flags 6 bits8 Flow control 16 bits9 CRC 16 16 bits10 Urgent pointer 16 bits11 Options 16 bits

TCP PacketTCP Packet

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Network and Transport Network and Transport LayersLayers

The transport & network layers sit between the application layer and the data link layer

They accept messages from the application layer, format, and address them for transmission by the data link layer

Both the sender and receiver have to agree on the rules or protocols that govern how their network layers will communicate with each other.

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Transport ProtocolTransport Protocol

A transport protocol is responsible for:

End-to-end delivery of the message Breaking large messages into packets for

transmission and reassembling them at the receiver’s end (packetizing)

Determining the correct network layer and data link layer addresses (addressing)

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Network ProtocolNetwork Protocol

A network protocol is responsible for:

Determining where the message should be send next on its way to its final destination (routing)

Selecting the best path from computer to computer through the network

Can share the addressing function with the transport layer

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ProtocolsProtocols There are many transport and network

protocols They all perform the same or similar functions They are incompatible with each other Vendors now provide software with

multiprotocol stacks

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ProtocolsProtocols

The four most commonly used protocols are:

TCP/IP IPX/SPX X.25 SNA

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IP Packet version 4 vs 6IP Packet version 4 vs 6

1 2 3 4 5 6 7 8 9 10 11

1 Version number 4 bits2 Header length 4 bits3 Type of Service 8 bits4 Total length 16 bits5 Identifiers 16 bits6 Flags 3 bits7 Packet offset 13 bits8 Hop limit 8 bits

IP4

9 Protocol 8 bits10 CRC 16 16 bits11 Source address 32 bits12 Destination Address 32 bits13 Options varies14 User data varies15 Priority 4 bits16 Flow name 8 bits17 Next header

1 15 16 4 17 14

IP6

12 13 14

11 (128 bits)8 12 (128 bits)

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IPX/SPXIPX/SPX Internetwork Packet Exchange / Sequenced

Packet Exchange Based on a routing protocol developed by

XeroX (mid 70’s) Primary network protocol used by Novell up

until they released version 5 of Netware

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IPX/SPXIPX/SPX

A combination of two protocols SPX - Sequenced Packet Exchange

Breaking the data into smaller packets Numbering them Ensuring each packet is reliably delivered Putting them in proper order at the destination

IPX - internetwork packet exchange Routing Addressing

Similar to TCP/IP

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IPX PacketIPX Packet

1 2 3 4 5 6 7 8 9 10 User Data

1 Checksum 2 bytes2 Length 2 byte3 Control 1 byte4 Type 1 byte5 Destination address 6 bytes6 Destination network address 4 bytes7 Destination socket 2 bytes8 Source address 6 bytes9 Source network address 4 bytes10 Source socket 2 bytes

IPX packet

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SPX PacketSPX Packet

1 2 3 4 5 6 7 User Data

1 Control 1 byte2 Type 1 byte3 Source ID 2 bytes4 Destination ID 2 bytes5 Sequence number 2 bytes6 ACK number 2 bytes7 Allocation number 2 bytes

SPX packet

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SNA SNA Systems network architecture Developed by IBM in 1974, IBM proprietary non-

industry standard protocol Transmission control layer performs packetizing Path control layer performs routing and addressing Requires special equipment to translate between lans

and mainframes Advanced peer-to-peer networking (APPN) was

developed by IBM to support TCP/IP Uses SDLC as its data link layer protocol

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SNA - 7 Layer Model SNA - 7 Layer Model

Presentation Layer

Data Flow Layer

Transmission Control

Path Control

Data Link Control

Physical Layer

Application Layer

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Transport and Network Transport and Network Protocols - SummaryProtocols - Summary

TCP/IP

IPX/SPX

X.25

SNA

Packetizing Routing andAddressing

TCP IP

IPX

X.3

Transmission Control Layer

SPX

PLP

Path Control Layer

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Transport Layer Transport Layer FunctionsFunctions

Linking to the application layer Packetizing Connection-oriented routing Connectionless routing Quality of service (qos)

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Linking to the Linking to the Application LayerApplication Layer

Each type of application has a unique port address

Application software sends both source and destination port addresses to the transport layer

Standard port addresses Port 80 - web server Port 21 - FTP Port 23 - telnet Port 25 - SMTP

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PacketizingPacketizing Breaking large data messages into smaller packets for

transmission through the network Size is dependent of data link layer protocol

Default size without protocol is 536 bits Size can be negotiated between sender and receiver

Numbering packets (sequencing) when needed Ensuring reliable delivery of every packet

Delivered one at a time or held until all have arrived at the destination

Reassembling and ordering packets at the destination

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Connection-Oriented Connection-Oriented RoutingRouting

Sets up a virtual circuit between sender and receiver Transport layer sends a special packet called a SYN

Virtual circuit appears to the application software to use point-to-point circuit-switching Actually uses store-and-forward switching

Network layer decides which route the packets will be travelling and sends them sequentially

High overhead - open/close of circuit

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Connectionless RoutingConnectionless Routing Each packet of a large transmission is treated

separately and makes its own way through the network

Packets may travel different routes and at different speeds through the network

Sequence number must be added to each packet by the Network layer

Network layer at receivers side must reassemble packet in sequence

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Connectionless vs. Connectionless vs. Connection-Oriented Connection-Oriented RoutingRouting

TCP/IP can operate as connection-oriented or connectionless.

When connection-oriented routing is needed, both TCP and IP are used. TCP establishes the virtual circuit and IP routes the messages.

When connectionless routing is desired, only IP is needed, and the TCP packet is replaced with a User Datagram Protocol (UDP) packet.

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Connectionless vs. Connectionless vs. Connection-Oriented Connection-Oriented RoutingRouting

IPX/SPX can also operate as either as connection-oriented or connectionless.

When connection-oriented routing is needed, both IPX and SPX are used. SPX establishes the virtual circuit and IPX routes the messages.

When connectionless routing is desired, only IPX is needed.

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Quality of Service (QoS) RoutingQuality of Service (QoS) Routing

Special kind of connection-oriented dynamic routing Packets are assigned different priorities

Depending on the type of packet sent Different classes of service are defined to determine the priority

Transport layer specifies the class of service when requesting virtual circuit

Each path designed to support different service classes Qos protocols

Rsvp Rtsp Rtp

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AddressingAddressing

Application Layer

Network Layer

Data Link Layer

Example Software

ExampleAddress

Web Browser

IP

Ethernet

www.cob.niu.edu

131.156.120.128

00-0C-00-F5-03-5A

Address

Key ConceptEach computer has several addresses, each used by a different layer.

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Assigning AddressAssigning Address At the application layer

Server names are specified in a software configuration file

Most servers have an application address, clients are beginning to depending on the operating system

A network standards group must approve all server names to insure that the addresses are unique

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Assigning AddressAssigning Address At the Network Layer

Network layer software has a configuration file that specifies the network layer address for the computer

Every network has a standards group that defines what addresses can be used by each organization

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Assigning AddressAssigning Address At the data link layer

Address is permanently coded in each network card

Every network card in the world has a unique address that differs from every other computer in the world

Addresses are coded by the vendor

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ICANNICANN Internet corporation for assigned names and

numbers (ICANN) Manages the assignment of application layer and network

layer addresses Sets the rules by which new domain names are created and

IP address numbers are assigned Manages a set of internet domains Authorizes private companies to become domain name

registrars Approves request for application layer addresses and assigns

IP numbers for those request Organizations can use any registered company for the specific

domain for a fee

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AddressingAddressingIPv4 address is four bytes longAddress

Class

Dotted DecimalNotation

A

B

C

0

0

0

0

0

0

1

1

1

1 1

7 8

15 16

23 24

31

31

31

1.0.0.0 to126.0.0.0

128.1.0.0 to191.254.0.0

192.0.1.0 to223.255.254.0

16 million user addresses

65,000 user addresses

254 addresses

Networknumber

Networknumber

Networknumber

Hostnumber

Hostnumber

Hostnumber

Assigned by ICANN

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SubnetsSubnets Each organization assigns IP addresses to

specific computers on its networks IP addresses are assigned so that all

computers on the same LAN have similar addresses

Each of these lans is known as a TCP/IP subnet

Any portion of the IP address can be designated as a subnet using a subnet mask*

* Subnet masks tell computers what part of an IP address is to be used to determine whether a destination is on the same or a different subnet

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Subnet AddressingSubnet Addressing

Figure 5-6

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Subnet AddressingSubnet AddressingExample 1

Suppose that the first two bytes are the subnet indicator with addresses of the form 131.156.x.x

Then, 131.156.29.156 and 131.156.34.215 would be on the same subnet.

The subnet mask would be 255.255.0.0, which corresponds to 11111111.11111111.00000000.00000000, where 1 indicates that the position is part of the subnet address and a 0 indicates that it is not.

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Subnet AddressingSubnet AddressingExample 2

Partial bytes can also be used as subnets.

For example, consider the subnet mask 255.255.255.128, which is 11111111.11111111.11111111.10000000.

Here, all computers with the same first three bytes and last byte from 128 to 254 would be on the same subnet.

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Providing AddressesProviding Addresses Providing addresses to networked computers

Static addressing Dynamic addressing

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Static AddressingStatic Addressing Each computer is given an address through a

configuration file Stored on individual computers Problems

Moves, changes, adds and deletes Individuals could change their own IP address Network renumbered

Companies do not have a good way of tracking the addresses

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Dynamic AddressingDynamic Addressing Server supplies a network layer address

automatically Each time user logs in For a specific lease period

Two standards for dynamic addressing Bootstrap protocol (bootp) - developed in 1985 Dynamic host control* protocol (DHCP), developed

in 1993

* some say C = configuration

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Dynamic AddressingDynamic Addressing Bootp and DHCP

Software installed on the client instructs the client to contact the server using data link layer addresses

Message asks server to assign the client a unique network layer address

Server runs corresponding software that sends the client its network address and subnet mask

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Leasing Leasing Bootp or DHCP server can either:

Assign the same network layer address to the client each time the client requests it (bootp)

Lease the network address from the next available on a list of authorized addresses for as long as the client is connected or for a specified amount of time -- common with isps and dial-up users (DHCP)

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Address ResolutionAddress Resolution The process of:

Translating an application layer address to a network address (server name resolution)

Translating the server name address to a data link layer address (data link layer address resolution)

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Address ResolutionAddress Resolution Server name resolution

Accomplished by the use of domain name service (DNS)

Computers called name servers provide these DNS services

Address data base includes: server names and their corresponding IP address

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Client computer

DNS Servernetmgr.cso.niu.edu131.156.1.11

DNS Request

LAN

LAN

Internet

DNS Request

Root DNS Server for .EDU

domain

Weber State University

Northern Illinois University

DNS Request

DNS Response

DNS Response

DNS Response DNS Serversol.acs.unt.edu137.90.2.122

Figure 5-7

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Address ResolutionAddress Resolution Data link layer address resolution

Broadcast message is sent to all computers in its subnet

“if your IP address is xxx.Yyy.Zzz.Ttt, please send your data link layer address”

Uses address resolution protocol (ARP)

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Network RoutingNetwork Routing The process of determining the route a

message will take through the network Centralized Decentralized

Static routing Dynamic routing Broadcast or multicast routing

Connectionless Connection-oriented routing

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Route and Route TableRoute and Route Table

Computer B Destination Route

A AC CD AE EF EG C

A

B C

G

E

D F

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Internet RoutesInternet Routes

UEN

WSU CanadaOther destinations

West Coast

Europe Asia

WSUDestination RouteUEN UtahOxford EuropeU of Toronto CanadaU of Singapore AsiaUC Stanford West CoastOther Other

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Types of RoutingTypes of Routing Centralized routing Static routing (decentralized) Dynamic routing (adaptive and decentralized)

Distance vector Link state

Other types Broadcast routing Multicast routing

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Centralized RoutingCentralized Routing All routing decisions are made by one

computer Main routing for star and mesh topologies Routing tables located on each computer

Central computer sends updated tables as needed Routing table tells the device where to send

messages

Simplicity - no wasted resources Hardware failures or changing conditions

cause table to be out of sync

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Decentralized RoutingDecentralized Routing Each of the following types of routing fall under the

heading of decentralized routing Each device makes its own routing decisions with the

use of a formal routing protocol Routing protocols are self-adjusting

Can automatically adapt to changes in the network configuration

Drawbacks Slows down the network with status messages Requires more processing by each computer

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Static RoutingStatic Routing Routing table developed by the network

manager or some type of committee Initial table sent to each computer which then

updates the routing table as needed Reroutes as needed with down or removed circuits Updated when new devices announce their

presence Used in relatively static networks that have few

routing options

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Dynamic Routing Dynamic Routing (Adaptive)(Adaptive) Routing messages over the fastest route

Used when there are multiple routes in the network Improves network performance by selecting the

fastest route to avoid bottlenecks or busy circuits Initial table developed by network manager Dynamically updated with changing conditions by

the devices themselves Monitors message transmission time or each

device reports how busy it is to avoid bottlenecks Disadvantages

Requires more processing by each computer “Wastes” network capacity

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Dynamic Routing Dynamic Routing (Adaptive)(Adaptive)

Distance vector dynamic routing The number of hops along a route Exchange information with the neighboring computers every

few minutes

Link state dynamic routing The number of hops along a route The speed of the circuits on the route How busy the route is Exchanges information with other routing devices every 15-

30 minutes Tries to determine the fastest route Converges reliable routing information more quickly

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Routing ProtocolsRouting Protocols

RIP, IGP, OSPF, EGP, BGP Distance vector routing protocols (RIP,

Appletalk,IPX, IGRP) Routers inform neighboring routers of table Closest router is used to route packets

Link State routing protocols (OSPF) Routers have at least a partial map of the network Changes are flooded throughout network Routes are recomputed

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Interior and Exterior Interior and Exterior RoutingRouting

Interior routing is within an autonomous system (collection of routers under a single administrative control)—RIP, OSPF

Exterior routing occurs between autonomous systems

Network access protocols operate at Layer 2. Transport of IP datagrams IP over point-to-point connections is used by ISP

when you dial in

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Routing ProtocolsRouting Protocols Border Gateway Protocol Internet Control Message Protocol Routing Information Protocol Open Shortest Path First Enhanced Interior Gateway Routing Protocol

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Routing ProtocolsRouting Protocols Internet protocols

BGP (border gateway protocol) Exchanges information between autonomous systems

about the condition of the internet Complex, hard to administer, exterior routing protocol

ICMP (internet control message protocol) Simple, interior routing protocol used with the internet Reports routing errors but is limited in the ability to update

RIP (routing information protocol) Dynamic distance vector interior routing protocol Counts the number of devices on each route Selects the route with the least number of devices

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Routing ProtocolsRouting Protocols OSPF (open shortest path first)

Link state interior routing protocol used on the internet Counts number of computers, network traffic, network error

rates to select the best route Doesn’t broadcast to all devices just to routing devices Preferred TCP/IP, but also used by IPX/SPX

EIGRP (enhanced interior gateway routing protocol) Link state interior routing protocol developed by CISCO Uses route transmission capacity, delay, reliability and load to

select best route Stores multiple routing tables

SAP (service advertisement protocol) Netware servers send SAP advertisements Novell’s broadcast protocol

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Broadcast RoutingBroadcast Routing

Sends the message to all computers on the network

Only computer with correct address processes the message

Used only in bus networks Wastes network bandwidth

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MulticastingMulticasting Similar to broadcasting Only works within one LAN or subnet Messages sent from one computer to another on the

network is called a unicast message Messages sent to a group of computers is called a multicast message

Targeting a specific work group IGMP (internet group management protocol)

Sends an IGMP multicast request to the routing computer Assigned a special class D IP address to identify the group The routing computer sets the data link layer address All participating machines will process messages sent to this

address Sends a IGMP message notifying of end of session

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Figures and TablesFigures and Tables

P. 245 figures 9.2 & 9.3 P. 261 figure 9.7