NT1210 Introduction to Networking

NT1210 Introduction to Networking

Unit 9: Chapter 9, The Internet

Objectives

Identify the major needs and stakeholders for computer networks and network applications.

Identify the classifications of networks and how they are applied to various types of enterprises.

Explain the functionality and use of typical network protocols.

Analyze network components and their primary functions in a typical data network from both logical and physical perspectives.

2

Objectives

Differentiate among major types of LAN and WAN technologies and specifications and determine how each is used in a data network.

Explain basic security requirements for networks. Plan and design an IP network by applying subnetting

skills. Assess a typical group of devices networked to another

group of devices through the Internet, identifying and explaining all major components and their respective functions.

3

Objectives

Relate how different technologies are used to access the Internet.

Define how IP routing is used in the Internet to move data from source to destination.

Define classless routing. Evaluate the need for NAT, PAT, CIDR, and IPv6 in

current networks.

4

The Internet as a Network of Networks

Figure 9-1Internet Access Links from TCP/IP Networks, Large and Small5


Internet Service Providers (ISPs) create Internet core Creates physical network for IP packets to travel

between enterprises and individual users

Figure 9-2The Internet Core, with Multiple Service Providers6


Connecting enterprises

Figure 9-3Typical Organizations Whose TCP/IP Networks Connect to the Internet7


Connecting to Internet edge: Part of Internet topology between ISP and customer (sits at edge of both networks)

Figure 9-4Comparing an Enterprise and ISP Network8


From network layer perspective: Internet access link acts like any other WAN link between routers

Figure 9-5T3 Serial Link Connection to the Internet9


Securing Internet edge: Enterprises use many security measures and devices to make Internet connection more secure Firewalls Intrusion Prevention Systems (IPS)

Example: Firewall sits in path that all packets take; IPS sits outside path so LAN switch forwards packets to IPS and it analyzes packets and watches for signs of problems

Figure 9-6An Example Case of Using an Enterprise Firewall and IPS10


Typical rules for enterprise firewallA. (Default): Allow inside clients to reach outside

servers in Internet

B. (Default): Disallow outside clients from sending packets to inside servers, unless another rule allows packet

C. (New Rule): Allow outside clients to connect to the two public web servers in DMZ

Example: Two attempts from users in Internet to connect to two different servers in enterprise Figure 9-7Firewall Allowing Connections to Public Web Servers Only

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Each WAN technology creates connection between user’s device and ISP

WAN connection might connect user’s device directly to WAN or may use router (not shown in example)

Figure 9-8Four Main Options for Individual Internet Access12


Connecting Customers to ISP Point-of-Presence (PoP): Each ISP has to create connections Connections between ISP’s customers

and ISP PoP Connections between all ISP’s PoPs

create ISP’s own network and allow all of customers to send packets to one another

Connections to other ISP networks form Internet core which allows all Internet hosts everywhere to send packets to each other

To create effective Internet access service, ISP needs number of PoPs in different locations

Figure 9-9ISP Point-of-Presence (PoP) Concept with Customer Access13


Example: Typical PoP with access routes using direct link to distribution router which connects to rest of ISP’s network

Figure 9-10Example of Dividing Responsibilities Inside an ISP PoP14


Connecting PoPs to create ISP network example ISP might put two more routers at centralized site and use 10-

Gbps Ethernet or SONET equivalent (called OC-192) on all links (center of graphic)

Figure 9-11Connecting All ISP PoP Routers to Create an ISP TCP/IP Network15


ISPs work together to create Internet core Internet core connects

all ISPs to all other ISPs (sometimes directly; sometimes indirectly)

Result: All ISPs can send packets to hosts connected to every other ISP

Figure 9-12Creating the Internet Core: Connections Between Large ISPs16


Tier 2 ISPs rely on connections to Tier 1 ISPs for some of their connections to Internet

Tier 2 ISPs connect to one or more Tier 1 ISPs rather than connecting to ALL Tier 1 ISPs across globe

Figure 9-13Connectivity Between Tier 1 and Tier 2 ISPs17


Other providers of Internet services: Companies who provide services available through Internet Web hosting Search engines Social media Cloud services

Figure 9-14Other Service Providers Connected to the Internet18


Other providers of Internet services Web Hosting: Customer picks URL for its website, creates

content for website, and puts website files onto servers that sit at web hosting company

Search Engine: Computers inside service provider’s network have programs that act like web browsers, systematically getting copy of every web page they can find on Internet

Social Media: Service provider that builds web servers that provide framework for users to add their own content (text, photos, video, apps)

Cloud Services: Large variety of services available through Internet

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Web hosting example: Company website (www.example.com) exists on servers owned by web hosting company

When user browses to www.example.com, packets flow to/from servers at web hosting company

Figure 9-15Hosting a Web Site at a Web Hosting Service, Not in the Enterprise’s IP Network20

Internet Access Technologies

Phone line and analog modem (Layers 1 and 2) Internet access: When customer calls, Telco passes call to ISP PoP over phone line not being used at moment

Example: Two ISP customers with analog modems If ISP wants to support many concurrent users in PoP, they

need many modems Once dialed in, users’ PCs can send and receive bits with

ISP through R1

Figure 9-16Two ISP Customers Using Analog Modems and Analog Phone Lines21


PPP and DHCP: Together they help customer’s PC learn its public IP address, subnet mask, default gateway, and IP addresses of DNS servers so PCs can access Internet

Figure 9-17Role of PPP on a Analog Dial-up Circuit to an ISP22


Using analog phone lines for Internet access Analog modems use symmetric speeds: Upstream speed (from

customer to ISP) same as downstream speed (from Internet to customer)

For most Internet applications, more bytes flow downstream than upstream

Asymmetric service with faster downstream speeds actually works better

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Using analog phone lines for Internet access

Table 9-1Comparison Points: Analog Modem24

Name Analog ModemPhysical link Telco local loop Always on? No Allows voice at same time over same medium? No Asymmetric? (Faster downlink possible?) No Approximate real-life downlink speeds 56 Kbps


Digital technologies from Telcos: Integrated Services Digital Network (ISDN) and Digital Subscriber Line (DSL) DSL requires changes to devices at end of local loop cabling,

including device in Telco CO Traditional CO voice

switch does not know what to do with DSL higher frequencies, so CO needs DSL Access Multiplexer (DSLAM) for DSL frequencies

Figure 9-18DSL Using Multiple Frequencies over a Single Local Loop25


Line splitter allows both analog phone and DSL modem to connect to same phone line and transmit simultaneously

Figure 9-19Home Cabling and Devices for DSL26


DSLAM uses Frequency Division Multiplexing (FDM) to separate voice and data frequencies in same electrical signal

DSLAM does not process data or voice; just passes data or voice off to correct device (router or traditional voice switch)

Figure 9-20DSLAM Multiplexes Voice to the PSTN and Data to the ISP27


DSL uses Data Link protocol PPP (Point-to-Point Protocol) to move data (IP packet encapsulated in PPP frame) to DSLAM which then moves PPP frame to ISP router

Figure 9-21PPP Encapsulated IP Packets Going from Home to ISP Router over DSL28


Differences and similarities between analog and DSL modems

Table 9-2Internet Access Link Comparison Points: Analog and DSL29

Name Analog Circuit DSL

Physical link Telco local loop Telco local loop

Always on? No Yes Allows voice at same time over same medium? No Yes

Asymmetric? (Faster downlink possible?) No Yes

Approximate real-life downlink speeds 56 Kbps 24 Mbps


Cable TV and cable modem: Cable modem uses different frequency channels than those used for video (TV) Cable Internet

service just like another TV channel

Instead of video, channel sends data

Figure 9-22Cable Internet Using Multiple Frequencies over a Single Circuit on Co-axial Cable30


Cable modem example: Cable modem feed comes from same cable as TV connection

Figure 9-23Home Cabling and Devices for Cable Internet31


Fiber to the Neighborhood (FTTN): Fiber goes to front of neighborhood with coaxial rest of way to houses

Fiber to the Curb (FTTC): Fiber goes into neighborhood and is buried at curb (closer to homes)

Figure 9-24Hybrid Fiber Coax (HFC) and Fiber-to-the-Curb (FTTC)32


Head End: CATV (cable access TV) company’s equivalent of Telco’s Central Office (CO) Has space to hold various devices, including those that

connect to ends of HFC cables

Figure 9-25CMTS and Head End Multiplexes Video and Data 33


Differences and similarities between cable Internet, DSL, analog modems

Table 9-3Internet Access Link Comparison Points34

Name Analog Circuit DSL CablePhysical link Telco local loop Telco local loop CATV cable Always on? No Yes Yes Allows voice at same time over same medium? No Yes Yes

Asymmetric? (Faster downlink possible?) No Yes Yes

Approximate real-life downlink speeds 56 Kbps 24 Mbps 50 Mbps


Wireless Telco and 4G: Wireless WAN technology supports many devices (mobile phones, tablets, laptops or other computers)

Devices can have built-in wireless WAN card or can use wireless WAN expansion card

Figure 9-26Wireless WAN Examples35


Consumer Internet-access technologies use cabling already in most homes; makes it inexpensive and affordable

Figure 9-27Enterprise WAN Options Used as Internet Access Technologies36

Short Break

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Take 10

Network Layer Concepts Before Scarce IP Addresses

Individual IP addresses must be unique to each host connected to Internet before they can send or receive IP packets

Hosts use IP addresses based on class A, B, or C networks

Addresses can not be assigned randomly Organized IP addresses helps routers to build usable

routing tables of networks Makes routing tables shorter and routing more efficient

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Network Layer Concepts Before Scarce IP Addresses Many different organizations (typically part of some not-

for-profit organization) work together to assign IP addresses for Internet worldwide IANA: Part of ICANN (Internet Corporation for Assigned Names

and Numbers) works with five worldwide regional organizations to manage address assignment process

Table 9-4Regional Internet Registries (RIRs)39

Name Locations ServedAfriNIC Africa APNIC Asia Pacific ARIN North America LACNIC Latin America, Caribbean RIPE NCC Europe, Middle East, Central Asia

Network Layer Concepts Before Scarce IP Addresses Early days of Internet: Original rule for assigning

addresses was for each company to use one classful IP network for its network When company wanted to

connect to Internet, it applied to IANA for classful network

IANA reviewed application and assigned network ID

Figure 9-29IANA Assigned Classful IP Network Numbers40

Network Layer Concepts Before Scarce IP Addresses IANA IP network assignments followed these general

rules:1. Only assign network IDs not yet

assigned to any other enterprise2. Assign class of network just large

enough to meet need of enterprise At end of process, each

enterprise had public address that fell into class A, B, or C IP address from public network

could be used to send packets to any other network in Internet

Figure 9-30Enterprises Subnet their One Classful IP Network41

Network Layer Concepts Before Scarce IP Addresses Example of SOHO address assignment in early days:

ISP1 reserved class C network 200.2.2.0 When PC2 and PC3 connect to ISP, they are given addresses

by ISP1 router

Figure 9-31Assigning IP Addresses to SOHO PCs42

Network Layer Concepts Before Scarce IP Addresses Border Gateway Protocol (BGP): Internet IP routing

protocol Prefers routes through less

expensive links Creates large routing tables

Figure 9-32BGP: Choosing Routes (Indirectly) Based on Business Rules 43

Network Layer Concepts Before Scarce IP Addresses In Internet core, routing tables have grown to over

400,000 routes So BGP built to be better able to handle larger

numbers of routes

Figure 9-33Scale of Internet Routing Tables: Large Enterprise Vs. Internet Core Routers 44

Network Layer Concepts Before Scarce IP Addresses Once classful network

has been assigned to company, all routers in Internet core need to know how to forward packets so they can reach ISP connected to company

Figure 9-34Internet Routing: IP Routes to Each Classful IP Network45

Network Layer Concepts Before Scarce IP Addresses Routers receive packets and then send them to next

router

Figure 9-35IP Forwarding (Routing) on Several ISP Routers 46

Network Layer Concepts Before Scarce IP Addresses Single-homed connection means that enterprise has

only one WAN link connecting to ISP

Figure 9-36Single-Homed Connection with Default Route 47

Network Layer Concepts Before Scarce IP Addresses Dual-homed Internet connection means enterprise has

two (or more) connections to Internet Gives enterprise choice of

where to send Internet packets

Default route might not work well in suchnetwork designs

Figure 9-37Inefficient Routes With Dual-homed Internet Connections 48

Network Layer Concepts Before Scarce IP Addresses Dual-homed example: Enterprise uses BGP between

itself and both ISP1 and ISP2 ISP2’s router would

advertise routes for networks 22.0.0.0 and 23.0.0.0, and routers R1 and R2 view route to Internet through ISP2 as better route

Figure 9-38Partial BGP Updates 49


Example: User device connects to Internet without using router Host has OS that includes TCP/IP software IP software includes concept of default router When connected

to Internet, host’s default router setting refers to ISP router

Figure 9-39Default Routers and Default Routes 50

Network Layer Concepts Before Scarce IP Addresses Name resolution and Global DNS system: Creating

globally unique hostnames DNS names assigned by IANA Process for how

companies and individuals get and use hostnames in Internet similar to assigning IP addresses

Figure 9-40Review: IANA Assigns IP Networks 51

Network Layer Concepts Before Scarce IP Addresses To create globally unique hostnames, process relies on

domain names With this format, names exist as

characters with periods in between Subdomain: Last part of name

Figure 9-41Format and Examples Using Domain Names 52

Network Layer Concepts Before Scarce IP Addresses To ensure unique hostnames throughout Internet,

company or individual must register subdomains with IANA-authorized company

If requested name not already in use, agency registers name so no other entitycan use it

Figure 9-42IANA/Others Approve Subdomain Registrations 53

Network Layer Concepts Before Scarce IP Addresses Hostnames on LANs follow domain name format, too Administrative process ensures no two hostnames will

ever be same Enterprises must

not duplicate names inside company

Figure 9-43IANA/Others Approve Subdomain Registrations 54


Example: Name server for companies Ent-1, Ent-2, and Ent-3 In each case, name server

lists short version of name, along with IP address used by that host

Name server considers each short name to have correct subdomain at end of name

Figure 9-44DNS Servers and Distributed Server Configurations 55


DNS defines how world creates distributed database of hostnames and their addresses DNS server for each subdomain

knows all hostnames and IP addresses for that subdomain

Root DNS servers: Special DNS servers inside Internet know IP addresses of all DNS servers

DNS defines protocol that servers use to ask among all DNS servers to find DNS server for right subdomain

Figure 9-45Finding the Right DNS Server for a Domain Name in Another Company 56

Network Layer Concepts Before Scarce IP Addresses At this point, client does not yet know www.ent-1.com’s

IP address Step 5: Server 128.1.9.9 sends name

resolution request to DNS for subdomain server ent-1.com

Step 6: DNS server ent-1.com knows name “www.ent-1.com,” so replies with IP address 1.1.1.1

Step 7: DNS server replies to ClientA with IP address of 1.1.1.1 so Clientcan now send packet with correct IPaddress on it

Figure 9-46Getting a Response from the Authoritative DNS Server for Ent-1.com 57

Network Layer Concepts with Scarce IPv4 Addresses IPv4 address exhaustion

Became clear by late 1980s that world would run out of IPv4 addresses with current IP class plan

Original address assignment plan had problems in part because of sizes of classful IP networks and number of each that existed

Table 9-4Number and Sizes of Classful IP Networks58

Class Number of Networks Size (Number of Host Addresses)

A 126 224 – 2 (>16,000,000) B 16,384 216 – 2 (>65,000) C 2,097,192 28 – 2 (254)

Network Layer Concepts with Scarce IPv4 Addresses Example of IP address assignment: Enterprise asks for

Class B network from IANA IANA grants network

128.1.0.0 Internet routers

update routing tables with routes for 128.1.0.0; entire class B network must be in one place

Figure 9-47Wasted IP Addresses: Got 65,000, Need 50059

Network Layer Concepts with Scarce IPv4 Addresses Graph: Number of estimated

Internet hosts 1984 – 1992 Data derived primarily from RFC

1296, which collected growth data in part because of IP address exhaustion problem

Figure 9-48Approximate Number of Hosts Connected to the Internet, 1984 - 199260

Network Layer Concepts with Scarce IPv4 Addresses Classless Interdomain Routing (CIDR): One method to

deal with IP address depletion Used by IANA Each CIDR block is set of

consecutive IP addresses unique in Internet (same as classful IP networks)

Figure 9-49IANA Assigns to ISP; ISP Assigns Smaller CIDR Block to Customer61

Network Layer Concepts with Scarce IPv4 Addresses

CIDR reduces routing table growth with route aggregation Example: ISP1 has 3 customers, each of which has CIDR block

of public IP addresses Router R4 (part

of ISP1’s network) has routes for each customer’s CIDR block

Figure 9-50CIDR Address Assignment Creates Larger Routing Tables62

Network Layer Concepts with Scarce IPv4 Addresses Route aggregation requires worldwide IP address

assignment process to assign numbers in large, consecutive groups Large group first assigned

to large enterprise such as ISP

Then ISP assigns smaller CIDR blocks to its customers

Administrative process allows routers to create aggregate routes for original large blocks, rather than separate routes for each individual smaller block

Figure 9-51CIDR Route Aggregation Keeps Other ISP Routing Tables Smaller63

Network Layer Concepts with Scarce IPv4 Addresses Network Address Translation (NAT): Way to translate

multiple PRIVATE addresses to single PUBLIC address for Internet access

Figure 9-52Hosts with Public IP Addresses Connected to Servers in the Internet64

Network Layer Concepts with Scarce IPv4 Addresses Three different connections from one host Server maps IP address for each connection

Figure 9-53One Client Host with Three Application Connections65

Network Layer Concepts with Scarce IPv4 Addresses NAT combines connections into one

Example: Three real devices each connect to same real web server

Router implementing NAT makes all three connections look like they come from single host (128.1.1.4)

Figure 9-54NAT Function on a Router66

Network Layer Concepts with Scarce IPv4 Addresses Example using private and public IP addresses

Three separate enterprises use PRIVATE networks based on 10.0.0.0

Each company uses different PUBLIC IP address block to access Internet

Figure 9-55Three Enterprises Networks, Each Using Private Network 10.0.0.067

Network Layer Concepts with Scarce IPv4 Addresses Public and private IP addresses: RFC 1918 sets aside

several private IP network address blocks Enterprise can pick private address block, assign IP

addresses from that block, subnet that block, etc.

Table 9-5Private IP Networks68

Class Number of Networks Network IDs

A 1 10.0.0.0 B 16 172.16.0.0 - 172.31.0.0

C 256 All that begin 192.168 (192.168.0.0, 192.168.1.0, 192.168.2.0, and so on, through 192.168.255.0)

Network Layer Concepts with Scarce IPv4 Addresses Basic NAT mechanics: NAT translates (changes) IP

addresses inside IP headers as packets pass through device doing NAT Step 1: PC sends

packet to router Steps 2-3: Router

translates private IP to public IP

Step 4: Router sends updated packet to public Internet

Figure 9-56NAT Translating the Source Address in Packet from Inside to Outside69

Network Layer Concepts with Scarce IPv4 Addresses

NAT example, Part 2: Server replies to host Packet comes into NAT router with IP address of 200.1.1.1 Step 6: Router

consults its NAT table to translate packet’s addressto Client A’s IP address (10.1.1.1)

Step 7: Router forwards packet to Client A

Figure 9-57NAT Translating the Destination Address in Packet from Outside to Inside70

Network Layer Concepts with Scarce IPv4 Addresses Enterprise still needs some public IP addresses so can

access Internet and be accessible by users outside enterprise (e.g., for web services)1. For NAT devices

2. For hosts in enterprise that need static, public IP addresses (typically servers)

Figure 9-58Public and Private IP Addresses in the Enterprise71

Network Layer Concepts with Scarce IPv4 Addresses SOHO address assignment: Most SOHO connections to

Internet use small, consumer-grade routers that typically combine many functions into one device

Figure 9-59Various Roles of Consumer “Router”72

Network Layer Concepts with Scarce IPv4 Addresses Router typically has defaults such as

Dynamically uses one public IP address (from ISP) on WAN port

Uses that one public IP for NAT Makes WAN port “outside” port for NAT Processes traffic coming in from LAN ports with NAT Picks one private IP network to use on LAN (typically

192.168.1.0) Acts as DHCP server on LAN ports to lease IP addresses to all

hosts on LAN Acts as firewall, allowing Intranet clients to connect to Internet

and preventing Internet clients from getting onto Intranet

Figure 9-59Various Roles of Consumer “Router”73

Network Layer Concepts with Scarce IPv4 Addresses Example SOHO address assignment User can change router defaults

or use directly out of box as is

Figure 9-60Default Settings on a Consumer-Grade Integrated Router74

Summary - This Chapter… Explained how individual devices, some home-based

TCP/IP networks, corporate TCP/IP networks, and ISP TCP/IP networks connect to create the global Internet.

Showed the typical devices and connections used in a connection from a corporate TCP/IP network and an ISP.

Described how ISPs work together to create the Internet core.

Generally described the layer 1 and 2 features used when connecting to an ISP using analog modems, DSL modems, and cable modems.

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Summary - This Chapter… Compared and contrasted analog modems, DSL, and

cable as Internet access technologies. Explained IP routing in the Internet, in the direction

from Enterprise towards the Internet and from the Internet towards an Enterprise.

Listed the typical steps that occur when a client needs to do name resolution for a hostname that exists in a different DNS subdomain.

Compared and contrasted the public IP address assignment process that was used before IP address exhaustion, and after the introduction of CIDR.

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Summary - This Chapter… Explained the basic reasons why CIDR needed a route

aggregation feature, and how route aggregation helped fill that need.

Explained the fundamental concepts behind how NAT reduces the number of required public IP addresses.

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Questions? Comments?

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NT1210 Introduction to Networking

Documents

internet connection

internet topology

network components

network of networksfigure

network applications

internet access links

typical data network

internet access link