NT1210 Introduction to Networking - YPW · The Internet as a Network of Networks SiIt td Et...
Transcript of NT1210 Introduction to Networking - YPW · The Internet as a Network of Networks SiIt td Et...
ObjectivesObjectives
Id tif th j d d t k h ld f tIdentify the major needs and stakeholders for computer networks and network applications.
Identify the classifications of networks and how they areIdentify the classifications of networks and how they are applied to various types of enterprises.
Explain the functionality and use of typical networkExplain 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.
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ObjectivesObjectives
Diff ti t j t f LAN d WANDifferentiate 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 subnettingPlan 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 functionsfunctions.
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ObjectivesObjectives
R l t h diff t t h l i d tRelate how different technologies are used to access the Internet.
Define how IP routing is used in the Internet to moveDefine how IP routing is used in the Internet to move data from source to destination.
Define classless routing.Define classless routing.
Evaluate the need for NAT, PAT, CIDR, and IPv6 in current networks.
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The Internet as a Network of Networks
Figure 9-1Internet Access Links from TCP/IP Networks, Large and Small5
The Internet as a Network of Networks
I t t S i P id (ISP ) t I t tInternet Service Providers (ISPs) create Internet core
Creates physical network for IP packets to travel between enterprises and individual usersbetween enterprises and individual users
Figure 9-2The Internet Core, with Multiple Service Providers6
The Internet as a Network of Networks
C ti t iConnecting enterprises
Figure 9-3Typical Organizations Whose TCP/IP Networks Connect to the Internet7
The Internet as a Network of Networks
C ti t I t t dConnecting 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
The Internet as a Network of Networks
F t k l tiFrom network layer perspective: Internet access link acts like any other WAN link between yrouters
Figure 9-5T3 Serial Link Connection to the Internet9
The Internet as a Network of Networks
S i I t t d E t iSecuring Internet edge: Enterprises use many security measures and devices to make Internet connection more secure
Firewalls Intrusion Prevention Systems (IPS)
E l Fi ll it i thExample: Firewall sits in path that all packets take; IPS sits outside path so LAN switch pforwards packets to IPS and it analyzes packets and watches for signs of problemsfor signs of problems
Figure 9-6An Example Case of Using an Enterprise Firewall and IPS10
The Internet as a Network of Networks
T i l l f t i fi llTypical 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 packetanother rule allows packet
C. (New Rule): Allow outside clients to connect to the two public
b i DMZweb servers in DMZ
Example: Two attempts from users in Internet to connect to two different servers inInternet to connect to two different servers in enterprise
Figure 9-7Firewall Allowing Connections to Public Web Servers Only11
The Internet as a Network of Networks
E h WAN t h l t ti b tEach WAN technology creates connection between user’s device and ISP
WAN connection mightWAN 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
The Internet as a Network of Networks
Connecting Customers to ISP Point of Presence (PoP):Connecting Customers to ISP Point-of-Presence (PoP): Each ISP has to create connections
Connections between ISP’s customers d ISP P Pand ISP PoP
Connections between all ISP’s PoPs create ISP’s own network and allow all of customers to send packets to one anotherConnections 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
The Internet as a Network of Networks
E l T i l P P ith t i di tExample: 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
The Internet as a Network of Networks
C ti P P t t ISP t k lConnecting PoPs to create ISP network exampleISP might put two more routers at centralized site and use 10-Gbps Ethernet or SONET pequivalent (called OC-192) on all links (center of graphic)
Figure 9-11Connecting All ISP PoP Routers to Create an ISP TCP/IP Network15
The Internet as a Network of Networks
ISP k t th t t I t tISPs work together to create Internet core
Internet core connects all ISPs to all otherall ISPs to all other ISPs (sometimes directly; sometimes indirectly)
Result: All ISPs can send packets to hosts connectedpackets to hosts connected to every other ISP
Figure 9-12Creating the Internet Core: Connections Between Large ISPs16
The Internet as a Network of Networks
Ti 2 ISP l ti t Ti 1 ISP fTier 2 ISPs rely on connections to Tier 1 ISPs for some of their connections to Internet
Tier 2 ISPs connect to one orTier 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
The Internet as a Network of Networks
Other providers of Internet services: Companies whoOther providers of Internet services: Companies who provide services available through Internet
Web hostingSearch enginesSocial mediaCloud services
Figure 9-14Other Service Providers Connected to the Internet18
The Internet as a Network of Networks
Oth id f I t t iOther providers of Internet services Web Hosting: Customer picks URL for its website, creates content for website, and puts website files onto servers that sitcontent 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 systematicallyhave 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 f f (provide framework for users to add their own content (text,
photos, video, apps)
Cloud Services: Large variety of services available through g y gInternet
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The Internet as a Network of Networks
Web hosting example: Company websiteWeb 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
Ph li d l d (L 1 d 2) I t tPhone 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 momentp gExample: Two ISP customers with analog modems
If ISP wants to support many concurrent users in PoP, they need many modemsneed many modemsOnce 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
Internet Access Technologies
PPP d DHCP T th th h l t ’ PCPPP 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 g y,access Internet
Figure 9-17Role of PPP on a Analog Dial-up Circuit to an ISP22
Internet Access Technologies
U i l h li f I t tUsing analog phone lines for Internet accessAnalog 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 upstreamp
Asymmetric service with faster downstream speeds actually works better
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Internet Access Technologies
U i l h li f I t tUsing analog phone lines for Internet access
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
Table 9-1Comparison Points: Analog Modem24
Internet Access Technologies
Di it l t h l i f T l I t t d S iDigital 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 COTraditional CO voiceTraditional CO voice switch does not know what to do with DSL higher frequencies, g e eque c es,so CO needs DSL Access Multiplexer(DSLAM) for DSL frequencies
Figure 9-18DSL Using Multiple Frequencies over a Single Local Loop25
Internet Access Technologies
Li litt ll b th l h d DSL dLine splitter allows both analog phone and DSL modem to connect to same phone line and transmit simultaneouslyy
Figure 9-19Home Cabling and Devices for DSL26
Internet Access Technologies
DSLAM uses Frequency Division Multiplexing (FDM) to separate voice and data frequencies in same electrical signalgDSLAM does not process data or voice; just passes data or voice off to
t d icorrect device (router or traditional voice switch)
Figure 9-20DSLAM Multiplexes Voice to the PSTN and Data to the ISP27
Internet Access Technologies
DSL D t Li k t l PPP (P i t t P i tDSL 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
Internet Access Technologies
Diff d i il iti b t l d DSLDifferences and similarities between analog and DSL modems
N A l Ci it DSLName 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
A i t l lif d li k d 56 Kb 24 Mb
Table 9-2Internet Access Link Comparison Points: Analog and DSL29
Approximate real-life downlink speeds 56 Kbps 24 Mbps
Internet Access Technologies
C bl TV d bl d C bl dCable TV and cable modem: Cable modem uses different frequency channels than those used for video (TV)( )
Cable Internet service just like another TV channelanother TV channel
Instead of video, channel sends data
Figure 9-22Cable Internet Using Multiple Frequencies over a Single Circuit on Co-axial Cable30
Internet Access Technologies
C bl d l C bl d f d fCable modem example: Cable modem feed comes from same cable as TV connection
Figure 9-23Home Cabling and Devices for Cable Internet31
Internet Access Technologies
Fib t th N i hb h d (FTTN) Fib t f tFiber to the Neighborhood (FTTN): Fiber goes to front of neighborhood with coaxial rest of way to houses
Fiber to the Curb (FTTC): Fiber goes intoFiber 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
Internet Access Technologies
H d E d CATV ( bl TV) ’Head End: CATV (cable access TV) company’s equivalent of Telco’s Central Office (CO)
Has space to hold various devices including those thatHas 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
Internet Access Technologies
Diff d i il iti b t bl I t tDifferences and similarities between cable Internet, DSL, analog modems
Name Analog Circ it DSL CableName Analog Circuit DSL CablePhysical link Telco local loop Telco local loop CATV cable Always on? No Yes Yes yAllows voice at same time over same medium?
No Yes Yes
Asymmetric? (FasterAsymmetric? (Faster downlink possible?)
No Yes Yes
Approximate real-life do nlink speeds
56 Kbps 24 Mbps 50 Mbps
Table 9-3Internet Access Link Comparison Points34
downlink speeds
Internet Access Technologies
Wi l T l d 4G Wi l WAN t h lWireless Telco and 4G: Wireless WAN technology supports many devices (mobile phones, tablets, laptops or other computers)p )Devices can have built-in wireless WAN card or can use wireless WAN expansion card
Figure 9-26Wireless WAN Examples35
Internet Access Technologies
C I t t t h l i bliConsumer Internet-access technologies use cabling already in most homes; makes it inexpensive and affordable
Figure 9-27Enterprise WAN Options Used as Internet Access Technologies36
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
I di id l IP dd t b i t h h tIndividual IP addresses must be unique to each host connected to Internet before they can send or receive IP packetsp
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 IPNetwork Layer Concepts Before Scarce IP Addresses
M diff t i ti (t i ll t f tMany 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 processg g p
Name Locations ServedAfriNIC Africa APNIC Asia Pacific ARIN North America LACNIC Latin America, Caribbean
Table 9-4Regional Internet Registries (RIRs)39
,RIPE NCC Europe, Middle East, Central Asia
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
E l d f I t t O i i l l f i iEarly 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 networkto IANA for classful network
IANA reviewed application and assigned
t k IDnetwork ID
Figure 9-29IANA Assigned Classful IP Network Numbers40
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
IANA IP t k i t f ll d th lIANA IP network assignments followed these general rules:1. Only assign network IDs not yet y g y
assigned to any other enterprise2. Assign class of network just large
enough to meet need of enterpriseg p
At end of process, each enterprise had public address th t f ll i t l A B Cthat 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 IPNetwork Layer Concepts Before Scarce IP Addresses
E l f SOHO dd i t i l dExample 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 , y gby ISP1 router
Figure 9-31Assigning IP Addresses to SOHO PCs42
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
B d G t P t l (BGP) I t t IP tiBorder Gateway Protocol (BGP): Internet IP routing protocol
Prefers routes through lessPrefers 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 IPNetwork Layer Concepts Before Scarce IP Addresses
In Internet core, routing tables have grown to over 400,000 routes
S BGP b ilt t b b tt bl t h dl lSo 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 IPNetwork Layer Concepts Before Scarce IP Addresses
O l f l t kOnce classful network has been assigned to company, all routers in p y,Internet core need to know how to forward packets so they canpackets so they can reach ISP connected to company
Figure 9-34Internet Routing: IP Routes to Each Classful IP Network45
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
R t i k t d th d th t tRouters receive packets and then send them to next router
Figure 9-35IP Forwarding (Routing) on Several ISP Routers 46
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
Si l h d ti th t t i hSingle-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 IPNetwork Layer Concepts Before Scarce IP Addresses
D l h d I t t ti t i hDual-homed Internet connection means enterprise has two (or more) connections to Internet
Gives enterprise choice ofGives enterprise choice of where to send Internet packets
Default route might not work well in suchnetwork designsnetwork designs
Figure 9-37Inefficient Routes With Dual-homed Internet Connections 48
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
D l h d l E t i BGP b tDual-homed example: Enterprise uses BGP between itself and both ISP1 and ISP2
ISP2’s router wouldISP2 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 gas better route
Figure 9-38Partial BGP Updates 49
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
E l U d i t t I t t ith tExample: User device connects to Internet without using router
Host has OS that includes TCP/IP softwareHost has OS that includes TCP/IP software
IP software includes concept of default router
When connectedWhen 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 IPNetwork Layer Concepts Before Scarce IP Addresses
N l ti d Gl b l DNS t C tiName resolution and Global DNS system: Creating globally unique hostnames
DNS names assigned by IANADNS names assigned by IANA
Process for how companies andcompanies and individuals get and use hostnames in Internet similar to assigning IP addressessimilar to assigning IP addresses
Figure 9-40Review: IANA Assigns IP Networks 51
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
T t l b ll i h t liTo create globally unique hostnames, process relies on domain namesWith this format names exist asWith this format, names exist as characters with periods in between
Subdomain: Last part of nameSubdomain: Last part of name
Figure 9-41Format and Examples Using Domain Names 52
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
T i h t th h t I t tTo ensure unique hostnames throughout Internet, company or individual must register subdomains with IANA-authorized companyp y
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 IPNetwork Layer Concepts Before Scarce IP Addresses
H t LAN f ll d i f t tHostnames on LANs follow domain name format, too
Administrative process ensures no two hostnames will ever be sameever be same
Enterprises must not duplicate namesnot duplicate names inside company
Figure 9-43IANA/Others Approve Subdomain Registrations 54
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP AddressesE l N f i E t 1 E t 2 dExample: Name server for companies Ent-1, Ent-2, and Ent-3
In each case name serverIn each case, name server lists short version of name, along with IP address used byIP address used by that host
Name server considers each short name toeach short name to have correct subdomain at end of name
Figure 9-44DNS Servers and Distributed Server Configurations 55
Network Layer Concepts Before Scarce IPNetwork Layer Concepts Before Scarce IP Addresses
DNS d fi h ld t di t ib t d d t b fDNS defines how world creates distributed database of hostnames and their addresses
DNS server for each subdomain knows all hostnames and IP addresses for that subdomainRoot DNS servers: SpecialRoot DNS servers: Special DNS servers inside Internet know IP addresses of all DNS serversDNS 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 IPNetwork Layer Concepts Before Scarce IP Addresses
At thi i t li t d t t k t 1 ’At this point, client does not yet know www.ent-1.com’s IP address
Step 5: Server 128 1 9 9 sends nameStep 5: Server 128.1.9.9 sends name resolution request to DNS for subdomain server ent-1.comStep 6: DNS server ent 1 comStep 6: DNS server ent-1.com knows name “www.ent-1.com,” so replies with IP address 1.1.1.1Step 7: DNS server replies to ClientStep 7: DNS server replies to ClientA with IP address of 1.1.1.1 so Clientcan now send packet with correct IPaddress on itaddress on it
Figure 9-46Getting a Response from the Authoritative DNS Server for Ent-1.com 57
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
IP 4 dd h tiIPv4 address exhaustionBecame clear by late 1980s that world would run out of IPv4 addresses with current IP class planaddresses 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
ClassNumber of Networks
Size (Number of Host Addresses)
24A 126 224 – 2 (>16,000,000) B 16,384 216 – 2 (>65,000) C 2,097,192 28 – 2 (254)
Table 9-4Number and Sizes of Classful IP Networks58
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
E l f IP dd i t E t i k fExample of IP address assignment: Enterprise asks for Class B network from IANA
IANA grants networkIANA grants network 128.1.0.0
Internet routers d t tiupdate routing
tables with routes for 128.1.0.0; entire class B networkentire class B network must be in one place
Figure 9-47Wasted IP Addresses: Got 65,000, Need 50059
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
G h N b f ti t dGraph: Number of estimated Internet hosts 1984 – 1992
Data derived primarily from RFCData 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 IPv4Network Layer Concepts with Scarce IPv4 Addresses
Cl l I t d i R ti (CIDR) O th d tClassless Interdomain Routing (CIDR): One method to deal with IP address depletion
Used by IANAUsed by IANA
Each CIDR block is set of consecutive IPconsecutive IP addresses unique in Internet (same as classful IP networks)classful IP networks)
Figure 9-49IANA Assigns to ISP; ISP Assigns Smaller CIDR Block to Customer61
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
CIDR d ti t bl th ith tCIDR reduces routing table growth with route aggregation
Example: ISP1 has 3 customers each of which has CIDR blockExample: ISP1 has 3 customers, each of which has CIDR block of public IP addresses
Router R4 (part f ISP1’of ISP1’s
network) has routes for each customer’s CIDRcustomer s CIDR block
Figure 9-50CIDR Address Assignment Creates Larger Routing Tables62
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
R t ti i ld id IP ddRoute aggregation requires worldwide IP address assignment process to assign numbers in large, consecutive groupsg p
Large group first assigned to large enterprise such as ISPas 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 IPv4Network Layer Concepts with Scarce IPv4 Addresses
N t k Add T l ti (NAT) W t t l tNetwork 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 IPv4Network Layer Concepts with Scarce IPv4 Addresses
Th diff t ti f h tThree different connections from one hostServer maps IP address for each connection
Figure 9-53One Client Host with Three Application Connections65
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
NAT bi ti i tNAT combines connections into oneExample: Three real devices each connect to same real web serverRouter 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 IPv4Network Layer Concepts with Scarce IPv4 Addresses
E l i i t d bli IP ddExample using private and public IP addresses Three separate enterprises use PRIVATE networks based on 10.0.0.010.0.0.0
Each company uses different PUBLIC IP address block to access Internetto access Internet
Figure 9-55Three Enterprises Networks, Each Using Private Network 10.0.0.067
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
P bli d i t IP dd RFC 1918 t idPublic and private IP addresses: RFC 1918 sets aside several private IP network address blocks
Enterprise can pick private address block assign IPEnterprise can pick private address block, assign IP addresses from that block, subnet that block, etc.
ClassNumber 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)
Table 9-5Private IP Networks68
9 . 68. .0, a d so o , t oug 9 . 68. 55.0)
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
B i NAT h i NAT t l t ( h ) IPBasic NAT mechanics: NAT translates (changes) IP addresses inside IP headers as packets pass through device doing NATg
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 IPv4Network Layer Concepts with Scarce IPv4 Addresses
NAT example Part 2: Server replies to hostNAT example, Part 2: Server replies to hostPacket comes into NAT router with IP address of 200.1.1.1
Step 6: RouterStep 6: Router consults its NAT table to translate packet’s addresspto Client A’s IP address (10.1.1.1)
Step 7: RouterStep 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 IPv4Network Layer Concepts with Scarce IPv4 Addresses
E t i till d bli IP ddEnterprise still needs some public IP addresses so can access Internet and be accessible by users outside enterprise (e.g., for web services)p ( g , )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 IPv4Network Layer Concepts with Scarce IPv4 Addresses
SOHO dd i t M t SOHO ti tSOHO address assignment: Most SOHO connections to Internet use small, consumer-grade routers that typically combine many yp y yfunctions into one device
Figure 9-59Various Roles of Consumer “Router”72
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
R t t i ll h d f lt hRouter typically has defaults such asDynamically uses one public IP address (from ISP) on WAN portUses that one public IP for NATMakes WAN port “outside” port for NATProcesses traffic coming in from LAN ports with NATProcesses traffic coming in from LAN ports with NATPicks 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 allActs as DHCP server on LAN ports to lease IP addresses to all hosts on LANActs as firewall, allowing Intranet clients to connect to Internet and preventing Internet clients from getting onto Intranetand preventing Internet clients from getting onto Intranet
Figure 9-59Various Roles of Consumer “Router”73
Network Layer Concepts with Scarce IPv4Network Layer Concepts with Scarce IPv4 Addresses
E l SOHO dd i tExample SOHO address assignment
User can change router defaults or use directly out of boxor 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-basedExplained 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 ISPISP.
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 andCompared and contrasted analog modems, DSL, and cable as Internet access technologies.
Explained IP routing in the Internet, in the direction p g ,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 routeExplained 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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