Internetworking

Organizational Communications and Technologies

Prithvi Rao

H. John Heinz III School of Public Policy and Management

Carnegie Mellon University

Objectives To investigate use of bridges and routers

Define an internetwork

Recognize the importance of internetworking

List examples of relevant internetworking equiopment

Relate equipment back to protocols they use and the OSI layer in which they reside

Readings

Chapters 14 and 15

Business Data Communications

William Stallings and Richard Van Slyke

Internetworking

Distributed organizationsdistributed set of networksLAN islandscross functional workteams across traditional org. boundaries

Any interconnected set of diverse or homogeneous networks is called an INTERNET.

Each constituent network referred to as a Subnetwork or Subnet.

The Role of Architectures

User’s perception is that there is a single network

Devices that make this possible are repeaters, bridges, routers, and gateways

Internetworking requires an understanding of architectures and their associated protocols

Architectures: Some ExamplesOSI

TCP/IP

SNA

DNA

Recall the OSI Architecture

Application

Presentation

Session

Transport

Network

Data link

Physical

Networkservice

Users liaison

Users oftransportservice

A Simplified Architecture for File Transfer

Computer 1

Computer 2

File transferapplication

File transferapplication

Communicationsservice module

Communicationsservice module

Network accessmodule

Network accessmodule

Files and file transfer commands

Communications-related messages

Networkinterface

logic

Communicationsnetwork

Communications Architectures and Networks

Processes1 2( ) ( )

Transport

Networkaccess

Host C

Networkaccess

Host B

Communicationnetwork

Service access point address

Processes1 2 3

( )-( )-( )Transport

Peer to Peer CommunicationsArchitecture

Computer X

Application Record

A-send (Dest.host; Dest.SAP; Record)

Transport

TPDU

DSAP Record

Network access

DHost DSAP Record

Packet

TPDU

Record Application

Transport

Network access

Computer Y

DSAP Record

T-Send(DESt. Add, PDU)

Internetworking devices

Repeatersat the physical layer

Bridgesat the MAC layer

Routersat the network layer

Gatewaysat the network or higher layer

Repeater

Endsystem

Endsystem

Repeater

7654321 1 1

234567

Subnetwork Subnetwork

Allows multiple LAN segments to be interconnected at the physical layer. Extends physical coverage.

Bridges

A device that operates at Layer 2 of the OSI stack used to segment LAN’s

Acts as an address filtermaps MAC layer addresses to segmentspicks up packets on one LAN addressed to a destination on another LAN and passes those packets on.

Variants on this theme exist in the marketplace (e.g., brouters)

Bridge

Endsystem

Endsystem

Bridge

7654321

21 1 1

234567

Subnetwork Subnetwork

Routers

Devices that operate at Layer 3 of OSI Stack

Used to connect networks that may or may not be similar

Routers are a key component of enterprise networks and the Internet

Router

A router operates at layer 3 of OSI model

Endsystem

Endsystem

7654321

21 1 1

234567

Subnetwork Subnetwork

23

Router

Router OperationHost X

TCPIP

LLCMAC

Physical

Host Y

TCPIP

LLC

Physical

MAC

Router 1

LLCMAC

Physical

X.25-3X.25-2X.25-1

Router 2

LLCMAC

Physical

X.25-3X.25-2X.25-1

a a b c d dLAN A

Ethernet

WAN C

X.25 Subnet

LAN B

Token Ring

IP IP

Router Capabilities

Addressing schemesdifferences between LAN addressing schemes and X.25 schemes

Maximum packet sizesEthernet maximum is 1500 bytes while X.25 maximum is 1000 bytes

Interfacesimplement interfaces to the networks over which data is routed

Gateways

Good way to accommodate OSI and non OSI protocolsGateways use all seven layers of the OSI stack

Endsystem

Endsystem

7654321

Subnetwork Subnetwork

7654321

Gatewayapplication

Interconnecting diverse networks Suppose there are N protocols to

interconnect

Option 1: Have N(N-1) mappings

Option 2: Have one common protocol. Now we require 2N mappings

IP uses this approach.

TCP/IP

Core of the Internet: DOD developedPopular, mature protocol stack with large, market share

The DoD approach stems from extensive experimentation with the ARPANET.

ARPANET started in the late 1960s', and has grown to hundreds of nodes today.

TCP/IP Fundamental Principle of the DoD architecture

Communication between local and remote processes is achieved by first identifying the remote host and then locating the remote process within the remote host.

The network now needs to route data between hosts, without bothering about the remote process.

Hierarchical layering, with four layers: Application,

Transport, Internet, and Network.

Higher layers may bypass adjacent layers and directly access a lower layer (Efficient!)

A Comparison of the OSI and TCP/IP Communications Architectures

ProcessApplication

Presentation

Session

Transport

Network

Data link

Physical

Host-to-host

Internet

Networkaccess

OSI TCP/IP protocolsuite

Communication Using the TCP/IP

Router

IP

NAP 1 NAP 2

Endsystem

App

TCP

IP

NAP1

Subnet 1

Endsystem

App

TCP

IP

NAP2

Subnet2

Protocol Data Units in TCP/IPUser data

TCPheader

IPheader

Networkheader

Applicationbyte stream

TCPsegment

IPdatagram

Network-levelpacket

IP Basics Connectionless Datagram Network Protocol.

Designed with Internetworking in mind.

Core IP Functions

Support Fragmentation and Reassembly Routing Error Reporting

Error checking covers only the IP header.

IP Helper Protocols Internet Control & Management Protocol

(ICMP)

Address Resolution Protocol (ARP)

Domain Name Service (DNS)

Routing Protocols Interior: R(outing)IP, OSPF (Open Shortest Path First) Exterior: BGP (Border Gateway Protocol)

IP Addressing Hierarchical addressing scheme for

scalability.

Logic for addressing scheme Class based addressing

There would be a few very large networks (class A). There would be a large number of small networks (class

C). 32-bit addresses

Network and host parts Length of network and host parts depends on the

class of network.

IP Addressing Dotted decimal notation

128.102.16.10 (NS.NSAS.GOV) Class B addresses. Start with 10

NS.NASA.GOV has a globally unique address 128.102.16.10

netid is 128.102, assigned by Network Information Center (NIC)

subnetid is 16, assigned by NASA (in this case) hostid is 10, assigned by NASA Lab(I n this case)

Broadcast Address: Hostid is all 1's.

IP Routing Classless Inter-Domain Routing (CIDR)

introduced in the early 90s to improve address space usage

IPv6 Changes 128-bit address length class less routing hooks for QoS

Location of hosts on the Internet How do hosts find each other on the

internet? Need Physical Address. Relationship between Physical Addresses and IP

Addresses. Ethernet addresses are 48-bits. IP addresses are 32-bits. Address Mapping is done

by the network. Each machine has an associated (IP,NPA) address

pair. Broadcast Address Resolution Packet using

the Address Resolution Protocol (ARP)

Controlling the Internet Internet Control Message Protocol (ICMP)

ICMP Functions

Communicate errors back to host: destination unreachable, datagram errors, excessively long routes detected, other failures.

Testing destination reachability and status. Datagram flow control. Route change requests (redirect). Obtain information such as NPA and subnet mask.

Transport Layer Functions Provides an interface between higher layers and the

underlying network. End-to-End Reliable Connectivity between hosts. Connectivity is between ports on hosts. The port addresses are only locally unique.

In TCP, some standard ports are defined for telnet, ftp, mail.

End-to-end error checking may be provided.

Common transport protocols: User Datagram Protocol (UDP) Transmission Control Protocol (TCP) ISO Transport Protocol

User Datagram Protocol Connectionless datagram protocol with

low overhead Limited error checking or recovery.

Assumes a reliable network layer. UDP checksum is optional and need not be used.

Used commonly on LANs. UDP is used with SUN's network file system (NFS).

Port Number: Transport Service Access Point (TSAP) in OSI

Transport Control Protocol Reliable Transport Protocol

Assumes very little about the underlying network, and can be used with a variety of networks. Dial-up telephone lines Internet IP datagram service LANs High speed fiber optics network Low speed long haul network Wireless links

TCP Features TCP is Connection-oriented.

TCP provides end-to-end error checking.

TCP provides end-to-end flow control (sliding window flow control).

Full duplex connection.

Higher overhead.

Internet Administrative BodiesInternet Society (ISOC)

non-governmental international societyTechnology management

standards, RFC processInternet Architecture Board (IAB: www.iab.org)Internet Engineering Steering Group (IESG) Internet Engineering Task Force (IETF: www.ietf.org) Internet Assigned Number Authority (IANA: www.iana.org) RFC Editor

InterNICdomain name registry and IP network number assignment

Internet Administrative BodiesInternet Corporation for Assigned Names and Numbers (ICANN)non-govermental groupResponsible for assigning names and numbers for the Domain Name System (DNS)

Arose in an environment of controversy

Internet ServicesTCP/IP based application layer protocols

SMTP (email)HTTP (WWW)SNMP (network management)FTP (file transfer)telnet (terminal emulation)

Ubiquity of this standards compliant platform has profound implications

intra-organizational systemsintranets

inter-organizational systemsbusiness to business commerce, business to consumer

Internet-enabled ApplicationsPull technology

www, ftp

Push TechnologyPointcast

Using the WWW to increase reach

Customer access to internal systems

tracking of packagesfedex, ups,...

Mutual fund informationvanguard, fidelity

Frequent flier milesAmerican, Delta

Electronic Marketplaces

Amazon

bookstore on the webover 1 million titleslow prices

Export Administration Regulationsdeveloped and administered by NTIS$21/month for access to regulation database

Push technologies

Pointcastinformation bundled with advertisingbrings newspapers, CNN etc. as per user interests to the desktop

can be used as a screen saverupdates itself on predetermined schedule or on demand

available at www.pointcast.com

Summary Internetwork is a network of networks which must

be capable of connecting networks together.

Internetwork consists of a number of computer platforms, operating systems and network interfaces. Goal of open internetworking is to overcome these differences.

Repeaters, bridges, routers and gateways required for accomplishing communication outside single LAN.