qspiders - variable length-subnet-masks

Variable-Variable-Length Length Subnet Subnet MasksMasks

© 2001, Cisco Systems, Inc. 3-13-1

What Is a Variable-Length Subnet Mask?

HQ 172.16.0.0/16

HQ

172.16.1.0/24

172.16.2.0/24

HQ 172.16.0.0/16

What Is a Variable-Length Subnet Mask? (cont.)

172.16.14.32/27

172.16.14. 64/27

172.16.14.96/27C

B

A

–Subnet 172.16.14.0/24 is divided into smaller subnets:• Subnet with one mask at first (/27)

HQ

172.16.1.0/24

172.16.2.0/24

HQ 172.16.0.0/16


172.16.14.32/27

172.16.14. 64/27

172.16.14.96/27

• Subnet 172.16.14.0/24 is divided into smaller subnets:• Subnet with one mask at first (/27)• Then further subnet one of the unused /27 subnets into

multiple /30 subnets

C

B

A

HQ

172.16.1.0/24

172.16.2.0/24

HQ 172.16.0.0/16172.16.14.136/30

172.16.14.132/30

172.16.14.140/30


Calculating VLSMs

Subnetted Address: 172.16.32.0/20In Binary 10101100. 00010000.00100000.00000000

Calculating VLSMs (cont.)

VLSM Address: 172.16.32.0/26In Binary 10101100. 00010000.00100000.00000000


Network Subnet VLSM subnet

Host

10101100 . 00010000 .0010 0000.00 000000=172.16.32.0/261st subnet:






1st subnet: 10101100 . 00010000 .0010 0000.00 000000=172.16.32.0/26172 . 16 .0010 0000.01 000000=172.16.32.64/26172 . 16 .0010 0000.10 000000=172.16.32.128/26172 . 16 .0010 0000. 1 000000=172.16.32.192/26172 . 16 .0010 0001.00 000000=172.16.33.0/26

Network Subnet VLSM Subnet

Host

1

2nd subnet:3rd subnet:4th subnet:5th subnet:


A Working VLSM Example

Derived from the 172.16.32.0/20 Subnet

A Working VLSM Example (cont.)

172.16.32.0/26

172.16.32.64/26

172.16.32.128/26

172.16.32.192/26

26 bit mask(62 hosts)




172.16.32.0/26

172.16.32.64/26

172.16.32.128/26

172.16.32.192/26




172.16.33.0/30

172.16.33.4/30

172.16.33.8/30

172.16.33.12/30


30-Bit Mask(2 Hosts)

172.16.32.0/26

172.16.32.64/26

172.16.32.128/26

172.16.32.192/26

26-Bit Mask(62 Hosts)



Route Summarization

© 2001, Cisco Systems, Inc. 3-14

What Is Route Summarization?

Routing table172.16.25.0/24172.16.26.0/24172.16.27.0/24

172.16.27.0/24

172.16.26.0/24

172.16.25.0/24

A

What Is Route Summarization? (cont.)

• Routing protocols can summarize addresses of several networks into one address

I can route to the 172.16.0.0/16 network.

Routing Table172.16.0.0/16

B

Routing Table172.16.25.0/24172.16.26.0/24172.16.27.0/24

172.16.27.0/24

172.16.26.0/24

172.16.25.0/24

A

Summarizing Within an Octet

172.16.168.0/24 = 10101100 . 00010000 . 10101 000 . 00000000

Number of Common Bits = 21Summary: 172.16.168.0/21

Noncommon Bits = 11

172.16.169.0/24 = 172 . 16 . 10101 001 . 0

172.16.170.0/24 = 172 . 16 . 10101 010 . 0

172.16.171.0/24 = 172 . 16 . 10101 011 . 0

172.16.172.0/24 = 172 . 16 . 10101 100 . 0

172.16.173.0/24 = 172 . 16 . 10101 101 . 0

172.16.174.0/24 = 172 . 16 . 10101 110 . 0

172.16.175.0/24 = 172 . 16 . 10101 111 . 0

Summarizing Addresses in a VLSM-Designed Network

CorporateNetwork

172.16.0.0/16

172.16.64.0/20

172.16.128.0/20

172.16.32.64/26172.16.32.0/24

172.16.128.0/20

172.16.32.128/26

A

B

C

D172.16.64.0/20

ClasslessInterdomain

Routing© 2001, Cisco Systems, Inc. 3-19

Classless Interdomain Routing

• Mechanism developed to alleviate exhaustion of addresses and reduce routing table size• Blocks of Class C addresses assigned

to ISPs—ISPs assign subsets of address space to organizations• Blocks are summarized in routing tables

CIDR Example

ISP

H

B

192.168.8.0/24

192.168.9.0/24

192.168.15.0/24

• Networks 192.168.8.0/24 through 192.168.15.0/24 are summarized by the ISP in one advertisement 192.168.8.0/21

A

192.168.8.0/21

192.168.15.0/24

192.168.8.0/24

192.168.9.0/24

WAN Basics

• A network that serves users across a broad geographic area• Often uses transmission devices provided by public carriers (Pacific Bell, AT&T, etc.) • This service is commonly referred to as

“plain old telephone service” (POTS)•WANs function at the lower three layers of the OSI reference model• Physical layer, data link layer, and network

layer

What Is a WAN?

WAN Overview

Service Provider

• WANs connect sites• Connection requirements vary depending

on user requirements and cost

What is a WAN?

A WAN is a data communications network that covers a relatively broad geographic area and often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

WAN connection types

• Point-to-Point Links or Leased Lines• Circuit Switching• Packet Switching

Point-to-Point Links or Leased Lines

• A point-to-point link is also known as a leased line because its established path is permanent and fixed for each remote network reached through the carrier facilities.

Leased Line

• One connection per physical interface• Bandwidth: depends on interface type• Cost effective at 4–6 hours daily usage• Dedicated connections with predictable throughput• Permanent• Cost varies by distance

• Dedicated physical circuit established, maintained, and terminated through a carrier network for each communication session• Datagram and data stream transmissions• Operates like a normal telephone call• Example: ISDN

WANModem Modem

Circuit Switching

•Sets up line like a phone call. No data can transfer before the end-to-end connection is established.

•Uses dial-up modems and ISDN. It is used for low-bandwidth data transfers.

Circuit Switching

POTS Using Modem Dialup

• Widely available• Easy to set up• Dial on demand• Asynchronous transmission• Low cost, usage-based• Lower bandwidth access requirements

Telecommuters

Mobile Users

ModemCorporate Network

ServerModem

Access Router

Basic Telephone

Service

Integrated Services Digital Network (ISDN)

• High bandwidth•Up to 128 Kbps per basic rate interface • Dial on demand•Multiple channels• Fast connection time•Monthly rate plus cost-effective,

usage-based billing• Strictly digital

LAN Server

Company Network

Telecommuter/After-Hours, Work-at-Home

BRI2B+D

BRI/PRI23B+D

30B+D (Europe)

ISDN

• Network devices share a point-to-point link to transport packets from a source to a destination across a carrier network• Statistical multiplexing is used to enable devices to share

these circuits• Examples: ATM, Frame Relay, X.25

WANModem Modem

Multiplexing Demultiplexing

Packet Switching

•WAN switching method that allows you to sharebandwidth with other companies to save money.

•Think of packet switching networks as a party line. As long as you are not constantly transmit-ting data and are instead using bursty data transfers, packet switching can save you a lot of money. However, if you have constant data transfers,then you will need to get a leased line.

• Frame Relay and X.25 are packet-switching technologies. Speeds can range from 56Kbps to 2.048Mbps.

Packet Switching

Frame Relay

• Permanent, not dialup• Multiple connections per

physical interface (permanent virtual circuits)

• Efficient handling of bursty (peak performance period) data

• Guaranteed bandwidth (typical speeds are 56/64 Kbps, 256 Kbps, and 1.544 Mbps)—committed information rate (CIR)

• Cost varies greatly by region

Permanent Virtual Circuit (PVC)

X.25

• Very robust protocol for low-quality lines• Packet-switched• Bandwidth: 9.6 kbps–64 kbps• Well-established technology;

large installed base• Worldwide availability

X.25DCE

DTE DTEDCE

Asynchronous Transfer Mode (ATM)

• Technology capable of transferring voice, video, and data through private and public networks

• Uses VLSI technology to segment data, at high speeds, into units called cells• 5 bytes of header information• 48 bytes of payload• 53 bytes total

• Cells contain identifiers that specify the data stream to which they belong

• Primarily used in enterprise backbones or WAN links

DataDataHeaderHeader

55 4848

Cabling the WAN

Core_Server

core_sw_a

ISDN Cloud

LegendFastEthernet/EthernetISDNDedicated

core_sw_b core_sw_b

ISL

Leased Line/Frame Relay

WAN Physical Layer Implementations

• Physical layer implementations vary• Cable specifications define speed of link

PPP

Fram

e R

elay

EIA/TIA-232EIA/TIA-449

X.21 V.24 V.35HSSI

ISDN BRI (with PPP)

RJ-45NOTE: Pinouts are different than RJ-45

used in campus

HD

LC

Differentiating Between WAN Serial Connectors

Router connections

Network connections at the CSU/DSUEIA/TIA-232 EIA/TIA-449 EIA-530V.35 X.21

CSU/DSU

End user device

DTE

DCE

Service provider

Data Terminal EquipmentEnd of the user’s deviceon the WAN link

Data Communications Equipment• End of the WAN provider’s

side of the communication facility• DCE is responsible for clocking

DCEDTE

ModemCSU/DSU

S S

SSS S

DTE DTEDCE DCE

Serial Implementation ofDTE versus DCE

WAN Terminating Equipment

Modem

Data Terminal EquipmentDTE

Data Circuit-Terminating Equipment

The Service Providers The Service Providers EquipmentEquipment

DCE

EIA/TIA-232V.35X.21HSSI

To Corporate Network

The Customer’s The Customer’s EquipmentEquipment

WAN Provider(Carrier) Network

Physical Cable Types

Usually on the Customer’sPremises

Router

• Hubs

• Bridges

• Switches

• Routers

LAN/WAN Devices

Hub

• Device that serves as the center of a star Device that serves as the center of a star topology network, sometimes referred to topology network, sometimes referred to as a as a multiport repeatermultiport repeater, , no forwarding no forwarding intelligenceintelligence

Hubs123123

124124

125125

126126

127127

128128

Hub

DataData DataData

• Amplifies signals• Propagates signals through the network• Does not filter data packets based on destination• No path determination or switching• Used as network concentration point

Hubs Operate at Physical layer

A B C D

Physical

• All devices in the same collision domain• All devices in the same broadcast domain• Devices share the same bandwidth

Hubs: One Collision Domain

• More end stations means more collisions• CSMA/CD is used

Bridge

• Device that connects and passes packets Device that connects and passes packets between two network segments.between two network segments.

• More intelligent than hub—analyzes More intelligent than hub—analyzes incoming packets and forwards (or filters) incoming packets and forwards (or filters) them based on addressing information. them based on addressing information.

Bridge

Segment 1 Segment 2

123123

124124

125125

126126

127127

128128Corporate Intranet

Hub Hub

• More intelligent than a hub—can analyze incoming packets and forward (or filter) them based on addressing information• Collects and passes packets between two network segments • Maintains address tables

Bridge Example

Switches

• Use Use bridging technologybridging technology to to forward traffic between ports. forward traffic between ports.

• Provide full Provide full dedicateddedicated data transmission data transmission rate between two stations that are directly rate between two stations that are directly connected to the switch ports.connected to the switch ports.

• Build and maintain Build and maintain address address tablestables called content-addressable memory called content-addressable memory (CAM).(CAM).

10-MbpsUTP Cable

“Dedicated”

Workstation

3131

Switch

Corporate Intranet

3232

33 3636100 Mbps 100 Mbps

• Uses bridging technology to forward traffic (i.e. maintains address tables, and can filter)

• Provides full dedicated transmission rate between stations that are connected to switch ports

• Used in both local-area and in wide-area networking• All types available—Ethernet, Token Ring, ATM

Switching—“Dedicated” Media

3535

3434

• Each segment has its own collision domain• All segments are in the same broadcast domain

Data Link

Switches and Bridges Operate at Data Link Layer

OR1 2 3 1 24

Switches

• Each segment has its own collision domain• Broadcasts are

forwarded to all segments

Memory

Switch

Routers• Interconnect LANs and WANsInterconnect LANs and WANs• Provide path determination using metricsProvide path determination using metrics• Forward packets from one network to Forward packets from one network to

anotheranother• Control broadcasts to the networkControl broadcasts to the network

Routing TableNET INT Metric

124

S0S0E0

100

1.0 4.0

1.3E0

4.3S0

2.2

E0

2.1

S0

4.1

4.2

1.1

1.2

Routing TableNET INT Metric

124

E0S0S0

001

• Logical addressing allows for hierarchical network• Configuration required• Uses configured information to identify paths to networks

Network Layer Functions (cont.)

Routers: Operate at the Network Layer

• Broadcast control

• Multicast control

• Optimal path determination

• Traffic management

• Logical addressing

• Connects to WAN services

Using Routers to Provide Remote Access

Internet

Telecommuter

Branch Office

Modem or ISDN TA

Mobile User

Main Office

Network Device Domains

Hub Bridge Switch Router

Collision Domains:1 4 4 4

Broadcast Domains:1 1 1 4

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