local area networking chapter 8. knowledge concepts components of a lan transmission media transport...

Local Area Networking

Chapter 8

Knowledge Concepts

Components of a LAN Transmission media Transport Access methods Topologies Interconnection VLANs Switches and routers

Important Vocabulary

LAN Cabling system Broadband vs

baseband CSMA/CD Token Tree ISPF, RIP BGP-4

Bus Ring Star Switch Vlan Bridge Router learning Static vs dynamic

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.

Node Number/Access Determines Type

Most of the World Uses Ethernet

Ethernet Tree Topology

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

Throughput

•CSMA/CD works well for small numberOf nodes per wire

•Throughput defined as useful data thatCan go across wire

•PPS (packet per sec) or percentUtilization of wire speed

LANs Cheaper as Nodes Increase

Break-point

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

LAN Operating System Functions Optimized I/O

One of the main services provided by a server is disk access. Disk access consists of three components: seek, latency, and transfer.

I/O optimization attempts to reduce one or more of these disk access components.

Disk Configurations One of the functions of an OS is to implement a file

system. This involves allocating and deallocating disk space and keeping track of space allocated to each file.

Partitioning Sometimes it is beneficial to divide a single disk

drive in two or more partitions; each partition can be managed separately

LAN Operating System Functions (cont.)

Single Disk Volume A volume is a logical disk (a partition or collection of partitions) or

physical disk that has been formatted and can be used to store data by an OS.

Multiple Disk Volumes or Volume Sets Most LAN OSs allow multiple partitions or disks to be combined to

form a single logical partition. A volume created from multiple partitions is called a volume set.

RAID Level 0—Striping without parity Another capability provided with some LAN OSs is called a Redundant

Array of Inexpensive Disks (RAID) Level 0 or striping without parity. Multiple partitions on different disks can be combined to proved a single logical disk; striping with parity differs from a volume just described in that data is written to all partitions simultaneously.

Fault Tolerance

A LAN with fault tolerance allows the server to survive some failures that would ordinarily be disabling. Fault tolerance usually is provided by a combination of backup hardware components and software capable of using the backup hardware.

A level of fault tolerance also can be provided by using redundant arrays of inexpensive disks (RAID). There are six levels of RAID, but for fault tolerance we are concerned only with RAID Level 1 and RAID Level 5.

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

Backup Software

The software used to perform the backups is as important as the hardware. Backup software is responsible for reading the files being backed up and writing them to the backup device.

Backup devices often come with a backup/restore program (both capabilities are contained on one program), and most LAN system software includes a backup/restore module.

Some LAN administrators choose to purchase a separate, more functional backup system than the LAN or backup device versions.

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.

Primary Backup Technologies

Diskette backup

Hard drive, fixed

Hard drive, removable cartridge

Tape backup, 4mm or 1/4 inch

Tape backup, 8mm or VCR

Tape backup, 9-track

Optical drives

Digital versatile disks (when available)

1.44 MB

Multiple capacities

40 MB to over 1 G

To 15 GB

160 MB

2.2 GB

To 2.2 GB

To 100 MB

To 4 GB

10-14 GB

2.88 MB

60 MB

500 MB

15 GB

20 MB

150 MB

1.2 GB

70 GB (compressed)

Backup Functions

Back up all files

Differential backup

Back up all files modified since a particular date

Back up by directory

Back up automatically by time or calendar

Back up all but a list of files to be excluded

Start backup from workstation or server

Back up by interface to a database

Back up using wildcard characters in file names

Incremental backup

Maintain index on tape and disk

Maintain cross-reference of tape serial numbers and backup

Back up manually

Back up by list of files

Back up by index

Compress data

Back up multiple volumes

Generate reports

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

Gateways translate one network protocol into another, translate data formats, and open sessions between application programs, thus overcoming both hardware and software incompatibilities.

A gateway may be a stand-alone microcomputer with several NICs and special software, a FEP (Front End Processor) connected to a mainframe computer, or even a special circuit card in the network server.

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


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



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


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


SNA/LAN Incompatibilities Yield Multiple Networks

CSU/DSUT-1

MUX

Source routing bridge CSU/DSU

T-1 MUX

Source routing bridge

1.544 Mbps

Token ring LAN

PCPC

CSU/DSUMUX9.6 Kbps

3270

Mainframe computer

Front-end processor

Cluster controller

3270 terminal

Corporate Headquarters Branch Office

SNA Network

Local Area Network

Gateway

CSU/DSU MUXCluster

controller

Token ring LAN


TCP/IP Encapsulation

CSU/DSUT-1

MUX CSU/DSUT-1

MUX

Router with TCP/IP support

and source route bridging for token ring

T-1 1.544 Mbps

Token ring LAN

PCPC

3270

Mainframe computer

Front-end processor

Cluster controller

3270 terminal

Corporate Headquarters Branch Office

Gateway

Cluster controller

Token ring LAN

Router with TCP/IP support

and source route bridging for token ring


Switched Media Technologies

Over the past few years, there has been a major change in the way we think about LANs and backbone networks. LANs have traditionally used multipoint circuits, and WANs have traditionally used point-to-point circuits.

As the shared circuits in LANs and BNs (Backbone Networks) have become overloaded with traffic, networks are starting to use switched point-to-point circuits rather than shared multipoint circuits.

Switched Ethernet

The concept behind switched ethernet - and all switched media technologies - is simple; replace the LAN hub with a switch. Each computer now has its own dedicated point-to-point circuit.

Switched ethernet dramatically improves LAN performance. However, since much of the network traffic is to and from the server, the circuit to the server is often the network bottleneck.

Switched Ethernet

Switched Ethernet

One obvious solution is to increase the number of connections from the server to the switch so that traffic now can reach the server on several circuits.

Other solutions include: Full Duplex Ethernet (full duplex over traditional

10Base-T). 10/100 Switched Ethernet (combines 10Base-T

and 100Base-T). This is often used to provide 10 Mbps to the clients and 100 Mbps to the server.

Full Duplex Ethernet

Switched Ethernet

Switched Ethernet at Fish & Richardson

Switched Ethernet Site Networks

No Maximum Distance Spans

Hierarchies and Single Possible Paths

High Speeds and Low Prices

Ethernet Switched Networks

There are Distance Limits Between

Pairs of Switches 100 meters with UTP Longer with optical fiber

MaximumSeparation

100 m with UTPLonger with optical fiber

EthernetSwitch

Hierarchies

Ethernet Switches Must be Arranged in a Hierarchy Root is the top-level

EthernetSwitch

Root

Hierarchies

Usually, Fastest Switches are at the Top (Root)

GigabitEthernetCampusSwitch

100Base-XBuilding Switch

10Base-TWorkgroup

Switch

Hierarchies

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

X XEthernetSwitch

Hierarchies

Single Possible Path Simplifies Switch Forwarding Decisions When frame arrives, only one possible output port (no multiple

alternative routes to select among) Switch sends frame out that port

SimpleForwarding

DecisionEthernetSwitch

Hierarchies

Switches allow only a single path for each MAC destination address Associated with a single port on each

switch So switch forwarding table has one and

only one row for each MAC address

EthernetSwitch

AddressA3..B2..

Port35

Hierarchies

Ethernet switch only has to find the single row that matches the destination MAC address

Only has to examine half the rows on average; less if the table is alphabetized

Comparison at each row is a simple match of the frame and row MAC addresses

AddressA3..B2..

Port35

More on Switched Ethernet

Switch LearningPurchase ConsiderationsVLANsIntelligent Switched Network Design

How Much of a Packet Does a Switch Need?

Switch Learning

Switch Forwarding Table has Address-Port Pairs

Manual Entry is Too Time Consuming Many addresses Addresses change

Solution: Learn addresses automatically

AddressA3..B2..

Port35

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

Switch Purchasing Decisions

Maximum Number of MAC address-port entries Small switches may not be able to store

many MAC addresses

For addresses that cannot be stored, switch must act like a hub, broadcasting and so creating latency

AddressA1C9

Port15


Queue Size Incoming frames are placed in queues if they

cannot be processed immediately May have several queues

If queues are too small, frames will be lost during brief peak loads

SwitchMatrix

QueuesOutputPorts

InputPorts

Frames


Switching Matrix Receives input from multiple input ports,

via queues Switches each frame to the correct output

port

QueuesOutputPorts

InputPorts

FramesSwitch Matrix


Reliability through Redundancy Redundant power supplies and cooling fans

May even have redundant switch matrix for backup

SwitchMatrix

QueuesOutputPorts

InputPorts

Frames


Manageability Can be managed remotely from the network

administrator’s desk Network administrator can check on status of switch

Network administrator can modify how the switch functions

Remote management greatly reduces labor

SwitchMatrix

QueuesOutputPorts

InputPorts

Frames

Multiple Access

Network Segmentation

Switch Connections

Dedicated Segments

Routing Types

Routing and Addresses

GOLDMAN & RAWLES: ADC 3e FIG: 07-08

Address ProcessingFrom source workstation to default gateway router found on LAN A:

From LAN A router to next hop router towards ultimate destination as noted in routing table:

From LAN B router to locally attached ultimate destination workstation:

destination 0020AF A3580A

source 0020AF A24890

source 0020AF A3581F

source 0000C0 C04445

destination 0000C0 C13745

destination 0020AF A2492B

Data-Link

Data-Link

Data-Link

destination B:22

source A:16

Network

destination B:22

source A:16

Network

destination B:22

source A:16

Network

Source Workstation

Ultimate Destination Workstation

Network Address: A:16 Physical Address: 0000C0 C04445

Network Address: B:22 Physical Address: 0000C0 C13745

Network Address: C:1 Physical Address: 0020AF A3581F

Network Address: A:1 Physical Address: 0020AF A3580A

Network Address: B:1 Physical Address: 0020AF A24890

Network Address: C:12 Physical Address: 0020AF A2492B

default gateway router

InternetworkLink

LAN A

LAN B

Physical Topology

router

Network Address Translation

NIC address: 192.75.16.65

Workstation address: 192.168.1.22 port 7586

private network

Workstation address: 194.196.16.43 Port: 80

NATPacket: Source: 192.168.1.22 Port: 7586 Destination: 194.196.16.43 Port: 80

Packet: Source: 194.196.16.43 Port: 80 Destination: 192.168.1.22 Port: 7586



NAT Source/Destination Table

Private Source IP Address Private Source Assigned Port ID

192.168.1.22

192.168.1.23

192.168.1.24

192.168.1.25

61001

61002

61003

61004

..and so on.. ..and so on..

INTERNET


Router Installations

Branch Office router

Branch Office router

Dial-up router

Dial-up router

Central Site router

All configuration (multiple LAN and WAN links) and routing information

contained here.

1 LAN link 1 WAN link Only connects to Corporate Headquarters

as needed

1 LAN link 1 WAN link

Only decides whether packet destination is local or not.

LEA

SE

D

LIN

E o

r fr

ame

rela

y

DIA

L-U

P li

ne s

uch

as I

SD

N

CORPORATE HEADQUARTERS

local LAN local LAN local LAN

local LAN

local LAN


Routing Evolution Scenarios

LAN A

edge switch

LAN switch

edge switch

Enterprise Network

route server

Route Servers

ENTERPRISE NETWORK ROUTING INFORMATION

ROUTING AND SWITCHING LAYER

Distributed Routing

Distinct Layer 2 Switching and Layer 3 Routing

SWITCHING LAYER

LAN switch

ROUTING LAYER

router

LAN B

LAN C

LAN A

multilayer switch

multilayer switch

Enterprise Network

ENTERPRISE NETWORK ROUTING AND SWITCHING LAYER

LAN B

LAN C

LAN A

LAN B

LAN C

Enterprise Network

ENTERPRISE NETWORK


IP Address Classes


Class ID

1 1 0

(3 bits)

0

(1 bit)

1 0

(2 bits)

126 different Network IDs

(7 bits)

Network ID Host ID

(24 bits)

16,777,214 different Host IDs

CLASS A

Class IDCLASS C

Class IDCLASS B Host ID

(16 bits)

65,534 different Host IDs16,382 different Network IDs

(14 bits)

Network ID

2,097,150 different Network IDs

(21 bits)

Network ID Host ID

(8 bits)

254 different Host IDs

address packet totals to 32 bits



NOTE: The contents of each CLASS ID segment is constant for each CLASS.

IP Address Instruction


Dotted Decimal IP Address:

Binary IP Address:

110 234 9 202. . .

01101110 11101010 00001001 11001010

110 234 9 202Decimal Representation of Each Octet:

Masks

IP Addresses are Always Paired with a Second 32-bit Number Called a Mask

Two Types: Network Masks and Subnet Masks Network Mask Tells the Length of the Network

Part Subnet Mask Tells the length of the Network

Plus Subnet Parts (not just subnet part) IP Address will be paired with one or the other,

but not both simultaneously

Using Subnet Masks


IP Address (Dotted Decimal):

IP Address (Binary):

110 234 9 202. . .

01101110 11101010 00001001 11001010

01101110 11101010 00001001 11001010

segment address

node address

Original Binary IP Address:

11111111 00000000 00000000 00000000

01101110 11101010 00001001 11001010

Binary SubNet Mask:

Resulting Division:

Applying SubNet Mask: 255.128.0.0

01101110 11101010 00001001 11001010

segment address

node address

Original Binary IP Address:

11111111 11111111 00000000 00000000

01101110 11101010 00001001 11001010

Binary SubNet Mask:

Resulting Division:

Applying SubNet Mask: 255.255.0.0

Multiple Network Protocols

GOLDMAN & RAWLES: ADC 3e FIG: 07-28

2 NICs. IPX/SPX and TCP/IP supported. Multi-protocol routing enabled

NetWare Servers

Windows NT Server

NetWare Clients

Windows NT/2000 Server

Windows NT/2000 Clients

Windows '9x Client

IPX/SPX

TCP/IP

Multi- protocol routing

NIC 1

NIC 2

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

Protocols

A protocol is a standard for communication between peer processes, that is, processes at the same layer, but on different machines

HTTP: Browser and webserver application programs are at the same layer but on different machines

AppApp AppAppHTTPMessage

Protocols A protocol is a standard for

communication between peer processes, that is, processes at the same layer, but on different machines

TCP, IP, and PPP all have “protocol” as their final “P;” they are all protocols

TCP (Transmission Control Protocol) is the protocol governing communication between transport layer processes on two hosts

TransTrans TransTransTCPMessage

Layered Communication

Layers work togetherEncapsulation and De-encapsulation

Indirect Communication

Application programs on different machines cannot communicate directly They are on different machines!

BrowserBrowser

TransTrans

IntInt

DLDL

PhyPhy

User PC

Web AppWeb App

TransTrans

IntInt

DLDL

PhyPhy

Webserver

HTTP RequestHTTP Request

Layer Cooperation on the Source Host

Application layer process passes HTTP-request to transport layer processApplicationApplication

TransportTransport

InternetInternet

Data LinkData Link

HTTP RequestHTTP Request

PhysicalUser PC


Transport layer makes TCP segments HTTP message is the data field Adds TCP header fields shown earlier Transport process “encapsulates” HTTP

request within a TCP segment

HTTP RequestHTTP Request TCP-HTCP-H

TCP Segment

DataField

TCPHeader

Encapsulation

Encapsulation is delivering a message in the data field of another message TCP encapsulates HTTP request messages

Can also encapsulate other types of messages

HTTP RequestHTTP Request TCP-HTCP-H

TCP Segment

DataField

TCPHeader

Layer Cooperation on the Source Host Transport layer process passes the

TCP segment down to the internet layer process

ApplicationApplication

TransportTransport

InternetInternet

Data LinkData Link

TCP segmentTCP segment

PhysicalUser PC


Internet Layer Process Encapsulates TCP Segment within an IP packet An IP packet to deliver a TCP segment has

a TCP segment in its data field

TCP segmentTCP segment IP-HIP-H

Data IP Packet

DataField

IPHeader


The internet layer process passes the IP packet to the data link layer process Internet layer messages are called packets


TransportTransport

InternetInternet

Data LinkData Link

IP packetIP packet

PhysicalUser PC


Data Link Layer Encapsulates IP Packet Within a PPP Frame Data link layer messages are called

frames Data PPP frame has IP packet in data

field

PPP Frame Encapsulating an IP Packet

PPP-TPPP-T IP packetIP packet PPP-HPPP-H


The data link layer process passes the PPP frame to the physical layer process, which delivers it to the physical layer process on the first router, one bit at a time (no message at the physical layer)


TransportTransport

InternetInternet

Data LinkData Link

Physical (10110 …)User PC

PPP framePPP frameTo firstrouter

PPP-TPPP-T


Recap: Adding Headers and Trailers:


TransportTransport

InternetInternet

Data LinkData Link

HTTP msgHTTP msg

PhysicalUser PC

HTTP msgHTTP msg TCP-HTCP-H

HTTP msgHTTP msg TCP-HTCP-H IP-HIP-H

HTTP msgHTTP msg TCP-HTCP-H IP-HIP-H PPP-HPPP-H

Layer Cooperation on the Source Host Encapsulation in Layering

Whenever a process at Layer N (the application, transport, internet, or data link layer) creates a message,

That Layer N process passes the message down to the next-lower-layer process, the process at layer N-1

The N-1 process encapsulates the Layer N message by placing it in the data field of a Layer N-1 message and adding headers and perhaps trailers to create the full Layer N-1 Message


Small but important detail on naming Layer 3 (internet) messages are called

packets IP message is a packet

Layer 2 (data link) messages are called frames PPP message is called a frame

Layer Cooperation: Destination Host

Destination host reverses processes on the sending host Delivers HTTP message to the webserver application program


TransportTransport

InternetInternet

Data LinkData Link

PhysicalUser PC Webserver

Layer Cooperation: Destination Host

Successively pass up layer messages


TransportTransport

InternetInternet

Data LinkData Link

IP-PacketIP-Packet

DL-Frame (protocol unknown)containing IP packet in data field

DL-Frame (protocol unknown)containing IP packet in data field

PhysicalFinal Router Webserver

Data link layer program processes the data link frame’s header and trailer, deencapsulates the IP packet, and passes the IP packet to the next higher layer, the internet layer

Layer Cooperation: Destination Host Successively pass up layer messages

Other layers pass successive data fields (containing next-layer messages) up to the next higher layer


TransportTransport

InternetInternet

Data LinkData Link

HTTP msgHTTP msg

TCP segmentTCP segment

IP-PacketIP-Packet

DL-Frame (protocol unknown)DL-Frame (protocol unknown)


Layer Cooperation: Destination Host Successively pass up layer messages

Other layers process headers & trailers, pass up message in data field


TransportTransport

InternetInternet

Data LinkData Link


PPP-TPPP-T

HTTP msgHTTP msg

HTTP segHTTP seg TCP-HTCP-H

HTTP msgHTTP msg TCP-HTCP-H IP-HIP-H

HTTP msgHTTP msg TCP-HTCP-H IP-HIP-H PPP-HPPP-H

IP Packet

TCPsegment

HTTP msg

Router’s Use of Data-Link and Network Layer Addresses

Header Data Trailer

MAC Layer addresses

Used for point-to-point connections

Network Layer (IP, IPX) addresses

Used for end-to-end connections

MAC address of router which last processed this packet

MAC address of next HOP router

Addresses change with each HOP

Network layer address of original workstation

Network layer address of ultimate destination workstation

Addresses do NOT change

Source Address

Destination Address

Source Address

Destination Address

Network layer data field containing upper layer protocols and user data

Used by router to determine best path according to information contained in routing table.

(Embedded Network Layer Packet)

Data Link Layer Frame


Layer Cooperation on the First Router

So far, we have only looked at hosts But deencapsulation and encapsulation

also occur on EACH router

Frame arrives at a port on the first router Port’s data link layer process receives

the PPP frame containing an IP packet

Data LinkData Link Data LinkData Link

InternetInternet

PPP FramePPP Frame

First Router


Incoming Data Link Process on the Router Deencapsulates the IP packet from the PPP frame Passes the IP packet to the router’ internet layer

process


InternetInternetIP PacketIP Packet

First Router

Incoming Port on First Router


Routers only have physical, data link, and internet layer processes So internet layer process is the highest-layer

process on a router for router forwarding Internet layer process decides where to send the

packet next: another router or the destination host


InternetInternet

First Router


Internet layer process passes IP packet to data link layer process on the selected output port that will carry the IP packet to the next router or the destination host


InternetInternet

First Router

IP Packet

Selected Output Port on First Router


The data link and physical layer process on the selected port sends the frame encapsulating the IP packet onto the next router (or destination host)

InternetInternet

Data LinkData Link

InternetInternet

Data LinkData LinkFrame

Selected Output PortOn First Router

Input PortOn Next Router

(Or Destination Host)

PhysicalLayer


For router forwarding, routers only use physical, data link, and internet processes

Routers First Receive Frames Receiving interface deencapsulates the IP

packet, passes the packet to the internet layer process

Routers Then Send Frames Out On a different output interface (port) This requires encapsulating of the IP packet

in a data link layer frame

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

FDDI

•Based on the token ring design using 100 Mbps fiber connections.

• Allows for two concentric rings - inner ring can support data travel in opposite direction or work as backup.

• Token is attached to the outgoing packet, rather than waiting for the outgoing packet to circle the entire ring.

Gigabit Ethernet (IEEE802.3z)

Similar to 100Base-X, 1000Base-X is a set of standards that provide 1 Gbps. One problem with 1000Base-X is that using the standard CSMA/CD media access control on a shared network may cause problems.

For this reason, gigabit ethernet may remain primarily a backbone technology for use only in point-to-point full duplex data communications links.

Fast Ethernet at GMAC

Fiber Distributed Data Interface (FDDI)

FDDI is a token-passing ring network that operates at 100 Mbps over two-counter-rotating fiber optic cable rings.

It will support up to 500 stationson each ring

http://www.iol.unh.edu/training/fddi/maps/Ring.map

Topology

The FDDI standard assumes a maximum of 1000 stations and a 200k path that requires a repeater every 2k. The second ring is for backup.

Single attachment stations (SAS) and dual-attachment stations (DAS) are both computer that can connect to one or both of the rings, respectively.

If the cable in the FDDI ring is broken, the ring can still operate in a limited fashion.

Topology

Ring-Wrapping

DAS SAS

FDDI and Fault Tolerance

Dual ring--ring wrapping (works for 1 failure, only)

Optical by-pass— mirrors reflect light back by-pass failed device

Dual-homing—dual concentrators with one active and the other inactive

Ethernet Virtual LANs

Broadcasting Sometimes, station needs to send a frame to all

other stations; this is broadcasting

For example, servers send a frame to advertise their presence with a broadcast message every minute or so


Broadcasting with Ethernet Switches Broadcaster sets the destination MAC

address to all ones (48 ones) When switch sees this address, it broadcasts

frame out all stations All stations read frames with this address

BroadcastFrame

EthernetSwitch


Broadcasting is a Problem in Large Switched Networks Server broadcasts go to all stations,

creating a great deal of network traffic Create congestion

BroadcastFrame


Ethernet switches do implement multicasting A server and the clients it serves are treated

as a single virtual LAN (VLAN) Can only communicate among themselves,

as if they were on their own LAN

Frame

MarketingVLAN Server

MarketingVLAN Client


VLAN Benefits

VLANs reduce traffic on the switched network

Other benefits

They provide weak security because clients cannot reach all servers (easily defeated but good first line of defense)

VLANs give ease of management because if a user changes organizational membership, VLAN membership is easily changed centrally

Bad Switch Organization

One Server for All Clients All traffic goes to and from server Bottlenecks: no simultaneous conversations No major benefits compared to hub

BottleneckEthernetSwitch

Bad Switch Organization

Multiple Servers for Clients Allows simultaneous conversations Brings switching’s main benefit

EthernetSwitch

Early Site Networks

Organization LANs (subnets) based on hubs Routers link hubs Hierarchy of Routers

Router

Hub

The Switching Revolution

Switches Push Routers to the Edge Router still needed at the edge of the site network

to communicate with outside world because routers handle expensive long-distance links very well

External

Switch


Layer 3 Switches Traditional switches operate at Layer 2; Switch based on

MAC addresses Layer 3 switches switch based on internet layer IP

addresses

External

Layer 3Switch


Layer 3 Switches Layer 3 switches are replacing many Layer 2

switches in site networks because of their ability to switch based on IP addresses

External

Layer 3Switch


Layer 3 Switches versus Routers Layer 3 switches are much faster than routers

Layer 3 switches cost less than routers

External

Layer 3Switch


Layer 3 Switches versus Routers Layer 3 switches rarely support Layer 2 WAN protocols

Routers usually are still needed at the edge of the site network, to communicate with external links

External

Layer 3Switch


Routers Forward based on IP

addresses and other internet layer addresses

Expensive and slow

Handle multiple internet layer protocols

Handle multiple LAN and WAN subnet protocols

Layer 3 Switches

Forward based on IP addresses, sometimes IPX addressesInexpensive and Fast

Do not handle multiple internet layer protocols

Do not handle multiple LAN and WAN subnet protocols


Layer 4 Switches Examine port fields in TCP and UDP

These fields describe the application

Therefore, can switch based on application (to give priority by application, etc.)

Layer 4Switch

Congestion, Latency, and Remedies

Peak Loads

Congestion and Latency

Overprovisioning Capacity

Priority

Quality of Service

Traffic Shaping

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.

Use of Data-Link Addressing by Bridges

Data Link Layer Frame

Data Link Header Data Link Data Field Data Link Trailer

Source Address Destination Address

Contains MAC address of original source workstation

Contains MAC address of ultimate destination workstation

Upper layer protocols including network layer address information

These addresses are used by bridges to determine whether or not packets should be forwarded across the bridge.

Data Link layer addresses are NOT changed by bridges.


Bridges Interconnect

Connecting LANs

Bridges Connect Similar

Bridge Installations

Token ring 4Mbps MAU


Thin EthernetTransparent

local bridge


10Base-T Ethernet hub

Local protocol converting (frame translating converter) bridge

CSU/DSU

Token Ring Remote bridge

Token Ring Remote bridgeCSU/DSU

Token Ring bridge with speed conversion

16Mbps token ring 4Mbps token ring

DB 25 connection

DB 25 connection56 Kbps

DDS

UTP

UTP

UTP Token RingUTP Ethernet

UT

P

thin

co

ax


Bridge & Switch Combo

Frames Are Converted

Overall Internetworking Design Strategies

20% of LAN traffic travels

between LANs

80% of LAN traffic stays on local LAN

bridge LAN B

Segmentation

Micro-Segmentation

LAN switch

FDDI modules (100 Mbps)

backbone network router

backbone network router

10BaseT module (10Mbps)

10BaseT module (10Mbps)

LAN A

Server Isolation

LAN switch or router

hub hub

Hierarchical Networking

10BaseT hub 10BaseT hub


Storage Area Network

Links to Enterprise Network or MAN

Tape Servers


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


Layer 3Switch

Layer 4

Layer 2

Switch

LAN Switches and Virtual LANs

broadcast source

LAN switch

B

B

B

broadcast source

LAN switch

LAN Switch

broadcast traffic

Broadcasts to all ports on LAN switch.

Single Switch Virtual LANs

Broadcasts only to members of Virtual LAN.

broadcast traffic

A

Virtual LAN assignments

Virtual LAN "A" is a multi-switch Virtual LAN

B

B

B

broadcast source

LAN switch

Multi-Switch Virtual LANs

A

C

C

LAN switch

C

C

Proprietary switch-to-switch communications

high-speed backbone network

A

A

A

A

A

A

A


Layer 2 vs. Layer 3 Virtual LANs: An Architectural Comparison

B

A

BB

Layer 2 Virtual LANs

A


B

C

DD

C

D

Layer 2 LAN switch

Layer 2 LAN switch

routerCDB A


D

C

C

A

A

All traffic between virtual LANs is forwarded to the router. Each Virtual LAN has its own connection to the router. LAN switches differentiate between Virtual LANs based upon the MAC layer address.

B

B

Layer 3 Virtual LANs

A


B

D

C

D

Layer 3 LAN switch

Layer 3 LAN switch


D

C

C

A

A

Routing functionality is included within the Layer 3 LAN switch. Traffic between Virtual LANs is forwarded by the Layer 3 routing functionality. Traffic within Virtual LANs is forwarded by the Layer 2 bridging functionality.

B

A routing

routing

C

D

Virtual LAN B IPX only

Virtual LAN A IP only

Virtual LAN D IP only

Virtual LAN C IPX only

Enterprise Network

Enterprise Network


local area networking chapter 8. knowledge concepts components of a lan transmission media transport...

Documents

ethernet slide

hub slide

end slide

type slide

token ring slide

topology topology

disk access components

single disk volume