IMPORTANT MATERIAL

Chapters 8-11

Topology

Topology is the basic geometric layout of the network -- the way in which the computers on the network are interconnected.

Ethernet uses a bus topology (a high speed circuit and a limited distance between the computers, such as within one building).

Bus Topology

Terminators required on each end

Ring Topology

Data Flow

Token Ring

Star Topology

Wiring Hub

Preferred method for today’s LANs

Media Access Control Ethernet uses a contention-based

technique called Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

If two computers attempt to transmit at the same time, they detect the collision, send a jamming signal, wait a random amount of time, then re-broadcast.

Ethernet Tree Topology

•Each hub broadcasts to own segment•Misbehaving nodes will be shut off by the hub

Network Servers: Everything You Wanted to Know But Were Afraid to Ask! Servers use multiple processors

Very important to access-intensive operations

Multiple processors provide 50% improvement

Buses provide backbone internal support for data transfer

RAM provides a buffer for operations

It’s a RAID!

Disk arrays improve performance and redundancy

RAID (Redundant Array of Inexpensive Disks) is a method used to write across (stripe) multiple disks to improve performance and fault tolerance

RAID 1 and 5 most popular but all have problems

RAID

Disk 1 Disk 2

File

RAID 1--Mirrors data between disks

RAID 0--Stripes data between disks

Mirrored Disk Drives

Controller 1 Controller 2

File 1 File 1

File 2 File 2

DuplexedControllers

1 2

Raid Level 5 Technology

File 1 Part 1 File 1 Part 3File 1 ParityFile 1 Part 2

File 2 Part 2 File 2 Part 3 File 2 Part 1 File 1 Parity

Server

1 2 3 4

A Fault-Tolerant Duplexed Server

Dedicated High-SpeedConnection

Duplexed Servers

Disk Drive Disk Drive

Mirrored Disk Drives

Immediate and Recurring Costs of a LAN

Equipment upgrades

Documentation

Installation of cabling

System software installation

Creating user environments

Space required for new equipment

LAN management—personnel costs

Consumable supplies—toner, paper, etc.

Immediate Costs

Recurring Costs

Training users, operators, administrators

Site preparation

Hardware installation

Installing applications

Testing

Supplies and spares

Hardware and software maintenance

Training new users, administrators

Basic LAN Management Tasks

Add, delete users and groups

Set user environment

Install/remove printers

Maintain printers

Add/change/delete hardware

Add/change/delete hardware

Plan and implement changes

Make backups

Carry out recovery as necessary

Plan capacity needs

Serve as liaison with other network administrators

User/Group Oriented

General

Set user/group security

Solve user problems

Setup user/printer environment

Manage print jobs

Establish connections with other networks

Diagnose problems

Maintain operating procedures

Educate users

Monitor the network for problems and to gather statistics for capacity planning

Printer Oriented

Hardware/Software Oriented

Backup Devices

Removable Disk Drives Manual intervention is necessary for changing disk

cartridges, whereas some tape backup system provide tapes with much higher storage capacity and with automatic tape changing.

Hard-Disk Drives The arguments for and against this alternative are

much the same as those for diskettes. The major difference is that the capacity of hard-disk drives is greater than that of diskettes.

Backup Devices (cont.)

Optical Disk Drives Optical disk drives are gaining popularity as input,

output, and backup devices. The reasons for this are their decreasing costs and large storage capacity.

Magnetic Tape Drives A magnetic tape drive is the usual choice for a

backup device. Magnetic tapes are less expensive than the other options. They hold large volumes of data, are easy to use and store, and generally provide good performance.

Gateways

Gateways operate at the network layer and use network layer addresses in processing messages.

Gateways connect two or more LANs that use the same or different (usually different) data link and network protocols. They may connect the same or different kinds of cable.

Gateways process only those messages explicitly addressed to them.

Gateways

One of the most common uses of gateways is to enable LANs that use TCP/IP and Ethernet to communicate with IBM mainframes that use SNA.

The gateway provides both the basic system interconnection and the necessary translation between the protocols in both directions.

Gateways

Classic SNA Architecture

3270

Mainframe computer

modem

modem

3274 cluster controller

3274 cluster controller

3745 front-end processor

3270 terminals

3270 terminal

327032703270

3270 terminals

327032703270

GOLDMAN & RAWLES: ADC3e FIG. 09-24

Standalone PC 3270 Terminal Emulation

3270

Mainframe computer

modem modem

modem

modem

3274 cluster controller

3274 cluster controller

3745 front-end processor

3270 terminals

3270 terminal

PC with installed 3270 protocol

conversion hardware and software

PC with installed 3270 protocol

conversion hardware and software

327032703270

3270 terminals

327032703270

GOLDMAN & RAWLES: ADC3e FIG. 09-25

LAN-based SNA Gateways

3270

Mainframe computer

Remote PC or asynchronous "dumb"

terminal without any 3270 protocol conversion

hardware or software

modem

modem

cluster controller

cluster controller

front-end processor

3270 terminal

local gateway PC with 3270 hardware and software installed.

32703270

3270

Synchronous modems

3270

asynchronous modem

asynchronous modem

asynchronous modem

Remote PC or asynchronous "dumb"

terminal without any 3270 protocol conversion

hardware or software

Standalone protocol converter which

emulates both 3270 terminals and a 3174

cluster conntroller

Remote gateway PC with both 3270 terminal emulation

as well as 3274 cluster controller

emulation hardware and software

Standalone 3270 protocol

converter

asynchronous modem

GOLDMAN & RAWLES: ADC3e FIG. 09-26

Full Duplex Ethernet

Switched Ethernet

Switched Ethernet at Fish & Richardson

Hierarchies

Vulnerable to Single Points of Failure Switch or Link (trunk line between switches) Divide the network into pieces

X XEthernetSwitch

Switch Learning

Every Few Minutes, Switch Erases Switch Forwarding Table To eliminate obsolete information Relearning is very fast

Address Port

A1 BF C9

EthernetSwitch

Erased

Routing Types

Standards for Web Server Access

Layer Standard

Application HyperText Transport Protocol (HTTP)

Transport Transmission Control Protocol (TCP)

Internet Internet Protocol (IP);Messages are packets

Data Link Point-to-Point Protocol (PPP); Messages are frames

Physical Modem, telephone standards

OSI Networking Model

Layer 7Application

Layer 6Presentation

Layer 5Session

Layer 4Transport

Layer 3Network

Layer 2Data Link

Layer 1Physical

Application & OS Network Client Application & OS

Bit stream connectionprotocol

Packet construction, Transmission, &

reception

Packet control& sequencing error

control

Connection betweenClient & server

Data compression& decompression; dataEncryption/decryption

Provide network services

To OS through network client

Network Wiring & specifications

54321 12345

Session

Packets

Network card & drivers

Data Packet with Header & Trailer

Domain Name System (DNS)

Subtlety Organizations or ISPs have local DNS

hosts These hosts must know only local host

names and IP addresses For other host names, local DNS host

passes request to another DNS host

User PCInternetLayer

Process

LocalDNSHost

RemoteDNSHost

Domain Name System (DNS)

Subtlety Remote DNS host passes information

back to the local DNS host Local DNS host passes information back

to user PC Browser only talks to local DNS host

User PCInternetLayer

Process

LocalDNSHost

RemoteDNSHost

Autoconfiguration

Every computer attached to the Internet is a host Including desktop PCs

Every host must have an IP address Some hosts, such as routers and

webservers, get permanent IP addresses So that they can be found easily

Autoconfiguration

User PCs do not need permanent IP addresses They only need to be found within a use

session They usually are given temporary IP

addresses each time they use the Internet They may get a different IP address each

time they use the Internet

Autoconfiguration

Request-Response Cycle User software requests IP address for the user

PC in Autoconfiguration Request message Autoconfiguration Response message contains

temporary IP address to use in current session

User PCAutoconfiguration

Host

AutoconfigurationRequest

TemporaryIP Address in

Autoconfiguration Response

Autoconfiguration

Most popular autoconfiguration protocol is DHCP Dynamic Host Configuration Protocol Built into Windows after Win 3.1 Supplies host with temporary IP address

DHCP can give more information too Usually gives IP address of a default gateway

(Microsoft terminology for router) Can give IP address of a local DNS host Can give other information

The Peak Load Problem

Capacity Sufficient Most of the Time Otherwise, get bigger switches and trunk lines!

Brief Traffic Peaks can Exceed Capacity Frames will be delayed in queues or even lost if

queue gets fullCapacityTrafficPeak

Overprovisioning

Overprovisioning: Install More Capacity than Will be Needed Nearly All of the TimeWasteful of capacityStill, usually the cheapest solution today because of its simplicity

Overprovisioned Capacity

TrafficPeak

Priority

Assign Priorities to Frames High priority for time-sensitive applications (voice) Low priority for time-insensitive applications (e-mail) In traffic peaks, high-priority frames still get through Low-priority applications do not care about a brief delay for

their frames

High-PriorityFrame Goes

Low-Priority FrameWaits Briefly

Bridges•A bridge can be used to connect two similar LANs, such as two CSMA/CD LANs.

•A bridge can also be used to connect two closely similar LANs, such as a CSMA/CD LAN and a token ring LAN.

•The bridge examines the destination address in a frame and either forwards this frame onto the next LAN or does not.

•The bridge examines the source address in a frame and places this address in a routing table, to be used for future routing decisions.

Bridges Interconnect

Connecting LANs

Frames Are Converted

Storage Area Network

Links to Enterprise Network or MAN

Tape Servers

GOLDMAN & RAWLES: ADC3e FIG. 09-02

RAID Disk

ArraysOptical Juke

Boxes

Fibre Channel Switch

Storage Area Network

Gigabit Ethernet

ATM Packet over SONET

Relationship Between the OSI Model and Internetworking Devices

Switch

Application

Presentation

Session

Transport

Network

Datalink

Physical

Application

Presentation

Session

Transport

Network

Datalink

Physical

OSI Model Layer LAN 1

OSI Model Layer LAN 2

Internetworking Device

Bridge

Gateway

Repeater

Router

GOLDMAN & RAWLES: ADC3e FIG. 09-05

Layer 3Switch

Layer 4

Layer 2

Switch

Internet 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

TCP/IP

TCP performs the packetizing function Breaking data into smaller packets Numbering packets Ensuring reliable delivery of packets Ordering packets at the destination

Linking to the Application 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 (also port 20) Port 23 - telnet Port 25 - SMTP

Packetizing

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

Connection-Oriented Routing

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

Connectionless 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

Connectionless vs. Connection-Oriented Routing

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.

Quality 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

Addressing

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.

Route and Route Table

Computer B Destination Route

A AC CD AE EF EG C

A

B C

G

E

D F

Internet Routes

UEN

WSU CanadaOther destinations

West Coast

Europe Asia

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

Routing 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

Interior and Exterior Routing

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

Routing 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

Routing 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

Bandwidth and Expansion

Internet traffic doubles every 11 months Traffic increases due to changing nature

of applications—more video and music with high bandwidth

Streaming video requires 3-7 Mbps Video compression

MPEG standards

Broadband Requirements

High speed and capacity From terabits to petabits!

Bandwidth on demand Any time allocation

Bandwidth reservation Guarantee of needed bandwidth

Support of isochronous traffic Traffic with no tolerance for delay

QoS Provide variable service levels

Tunneling with a VPN

Why VPNs?

Improves ability to communicate outside of a company

Enables secure access Provides rapid provisioning of capacity

as needed

How Remote Access Via a VPN Works

VPN Characteristics

Logical network Isolates customer traffic on shared provider

facilities Looks like a private network Runs on either packet switched data network

or circuit-switched public network Can be deployed over a wide range of

network technologies Uses shared carrier infrastructure

Deployment Models

Customer-based Carriers install gateways, routers and

hardware on customer premises Customer manages security

Network-based Carrier houses all equipment at POP near

customer location

VPN Frameworks

Internet based Small ISPs provide local access services in a region Business users get end-to-end services from a

variety of suppliers Encryption used to isolate traffic and provide security Customer provides servers wit applications/content A RADIUS server is used to authenticate traffic for

access to application/Content servers RADIUS server is connected to a firewall

Provisioned VPNs

Packet-switched VPN that runs across ISP backbone using Frame Relay or ATM

Supports multiple protocols Provisioned services improve

performance by enabling guarantees of service (QoS)

3 Major VPN Applications

Intranets Sit-to-site connections

Remote Access Remote workers and outside customers Eliminates modems & remote access

routers Extranets

Suppliers have specific access

VPN Gateway Functions

Maintenance of a secure logical connection as a tunnel

Tunneling is encapsulation of a data packet within an IP packet

Remote ends of tunnel can be at edges of ISP or corporate boundary router

Traffic is routed as encyrpted

Key Tunneling Protocols

PPTP—Layer 2 in MS products L2TP –used by ISPs on backbone IPSec –covers encryption at 168 bit and

authenticated both ends of tunnel connection Works only in IP environment

VPN Security

Firewalls are used to control policies for data exchange between 2 networks

Routers can act as a firewall by managing packet traffic (filter)

Proxy servers used to separate internal network from public services

Authentication provided by RADIUS servers Uses CHAP (Challenge Handshake Authentication

Protocol) to authenticate Tokens issued with user password to server to verify

user access New tokens generated each time a user connects

Basic Encryption Terminology

Plaintext (aka cleartext): original, readable data

Ciphertext: scrambled form of plaintext Encryption: reversible conversion of

plaintext into ciphertext Decryption: conversion of ciphertext

back into plaintext Crack (aka break) code: decrypt

ciphertext without knowing key

Basic Encryption Terminology (cont’d)

Key: secret allowing encryption and decryption to be restricted to possessors of key

Symmetric encryption: encryption requiring a shared key for both encryption and decryption

Asymmetric encryption: algorithm using a different key for decryption than for encryption

Encryption Encoding plain text data to hide contents with cipher text Symmetric

Sender and receiver use same key Popular algorithms: DES, Triple DES, Blowfish

Asymmetric (PKI) Different keys with one key held publicly Verifies message through hashing (MD5) Types of public keys are RSA, Diffie-Hellman, PGP PKI uses digital certificates to authenticate users and

encrypt data Verisign and Entrust

US Digital Signature Law

USA: 15 USC §7006 Title 15: Commerce and Trade

Chapter 96: Electronic Signatures in Global and National Commerce

Based on S.761 (Sponsor Sens Abraham & Spencer) Introduced 1999-003-25 Came into force 2000-06-30 See Legal Information Institute entry athttp://www4.law.cornell.edu/uscode/15/

ch96.html#PC96

Electronic Payments

Credit card transactions Digital cash Micropayments

Credit Card Transactions

No documented case of interception of credit-card data while in transit through the Internet Most sites use Secure Sockets Layer (SSL) Credit-card information theft has occurred from

servers All sensitive data on Web servers should be

encrypted Safety of allowing a merchant to use credit-

card information depends on the merchant No worse to give info to reputable firm via Web than

to clerk who takes card away from view

Credit Cards & Escrow Allow buyer to register credit-card data with reputable firm

Merchant receives payment from escrow service Escrow service bills client credit card Insulates buyer from seller

Examples: VeriSign Cybercash http://www.cybercash.com Escrow.com http://www.escrow.com (for domain name

sales) Beseen BuyIt Button http://buyit.beseen.com Tradenable http://www.tradenable.com PayPal www.paypal.com

Digital Cash

All credit-card transactions result in electronic audit trail

Digital cash (aka e-cash) removes trail Load a device with credits Use device for transactions to transfer credits

Requires device that can prevent Counterfeiting (loading credits fraudulently) Theft (removing credits fraudulently)

Digital Cash (cont’d)

Mechanisms depend on smart cardsDevices size of credit card Include microprocessor, RAM, powerProgrammed with cryptographic tools to prevent

unauthorized modification of contents Interface allows merchant to deduct or refund

credits Examples include

eCash http://www.digiscash.comE-Cash Services http://www.ecashservices.com

Expensive Leased Lines

VPN Access as an Intranet

VPNs and Business

Before a VPN—Point-to-Point

After a VPN—Tunneled

Encryption and VPNs

Evaluating a VPN Solution

VoIP

Not yet a big player with less than 5% of market

Cost savings, enhanced voice services and new applications major advantages

VoIP gateways bridge circuit-switched PSTN and packet-switched Internet Gateways packetize, and compress voice, route

packets, authenticate users, and manage network of gateways

VoIP Hardware

Enterprise gateway Deployed between PBX and WAN device (router) for

call set-up,routing, and conversion VoIP routers

Voice cards perform packetization and compression functions in a router

IP PBX Distributed telephony servers that operat ein packt-

switched mode ISP VoIP gateways

Aggregate incoming traffic and routing

VoIP Infrastructure

VoIP Architecture

Implementing VoIP

VoIP Standards H.323

Based on ISDN and limited to point-to-point applications SIP

Application layer (signaling) protocol Establishes temp sessions for multimedia conferences,

telephony, mobile phone-to-instant messaging LDAP

Standard directory server technology for Internet Enables retrieval of information from multi-vendor

directories Used for free phone and Internet phone number hosting