IT220 Network Standards & Protocols. Unit 9: Chapter 9 The Internet

Transcription

1 IT220 Network Standards & Protocols Unit 9: Chapter 9 The Internet

2 3 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.

3 4 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.

4 5 Objectives 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. 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.

5 The Internet as a Network of Networks Internet Service Providers (ISPs) create Internet core Creates physical network for IP packets to travel between enterprises and individual users The Internet Core, with Multiple Service Providers 6 Figure 9-2

6 The Internet as a Network of Networks Typical Organizations Whose TCP/IP Networks Connect to the Internet 7 Figure 9-3

7 T3 Serial Link Connection to the Internet Figure Connecting to the Internet Edge Connecting to Internet edge: Part of Internet topology between ISP and customer (sits at edge of both networks) From network layer perspective: Internet access link acts like any other WAN link between routers

8 Securing the Internet Edge Enterprises use many security measures and devices to make Internet connection more secure Firewalls Intrusion Prevention Systems (IPS) An Example Case of Using an Enterprise Firewall and IPS 9 Figure 9-6

9 Securing the Internet Edge 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 An Example Case of Using an Enterprise Firewall and IPS 10 Figure 9-6

10 Securing the Internet Edge with a Firewall Typical rules for enterprise firewall A. (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 Firewall Allowing Connections to Public Web Servers Only 11 Figure 9-7

11 Securing the Internet Edge with a Firewall Example: Two attempts from users in Internet to connect to two different servers in enterprise Firewall Allowing Connections to Public Web Servers Only 12 Figure 9-7

12 Connecting to the WAN 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) Four Main Options for Individual Internet Access 13 Figure 9-8

13 Connecting to the WAN 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 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 14 Figure 9-9

14 Connecting to the WAN To create effective Internet access service, ISP needs number of PoPs in different locations 15 Figure 9-9

15 Internet Core 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) Connecting All ISP PoP Routers to Create an ISP TCP/IP Network 16 Figure 9-11

16 Internet Core 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 Creating the Internet Core: Connections Between Large ISPs 17 Figure 9-12

17 Internet Core: Tier 1, 2, 3 ISPs 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 Connectivity Between Tier 1 and Tier 2 ISPs 18 Figure 9-13

18 Internet Services Other Service Providers Connected to the Internet 19 Figure 9-14

19 Web Hosting Service Example Company website ( exists on servers owned by web hosting company When user browses to packets flow to/from servers at web hosting company Hosting a Web Site at a Web Hosting Service, Not in the Enterprise s IP Network 20 Figure 9-15

20 Internet Access Technologies: Analog Modems 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 Two ISP Customers Using Analog Modems and Analog Phone Lines 21 Figure 9-16

21 Internet Access Technologies: PPP & DHCP PPP and DHCP: Help customer s PC learn its public IP address, subnet mask, default gateway, and IP addresses of DNS servers so PCs can access Internet Role of PPP on a Analog Dial-up Circuit to an ISP 22 Figure 9-17

22 Internet Access Technologies: ISDN, DSL 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 DSL Using Multiple Frequencies over a Single Local Loop 23 Figure 9-18

23 Internet Access Technologies: DSL Line splitter allows both analog phone and DSL modem to connect to same phone line and transmit simultaneously Home Cabling and Devices for DSL 24 Figure 9-19

24 Internet Access Technologies: DSL Multiplexing 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) DSLAM Multiplexes Voice to the PSTN and Data to the ISP 25 Figure 9-20

25 Internet Access Technologies: DSL and PPP 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 PPP Encapsulated IP Packets Going from Home to ISP Router over DSL 26 Figure 9-21

26 Internet Access Telco Technologies Comparison 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 Internet Access Link Comparison Points: Analog and DSL 27 Table 9-2

27 Internet Access Technologies: Cable 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 Cable Internet Using Multiple Frequencies over a Single Circuit on Co-axial Cable 28 Figure 9-22

28 Internet Access Technologies: Cable Example Home Cabling and Devices for Cable Internet 29 Figure 9-23

29 Internet Access Technologies: Cable 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 CMTS and Head End Multiplexes Video and Data 30 Figure 9-25

30 Internet Access Technologies: FTTN, FTTC Fiber to the Neighborhood: Fiber goes to front of neighborhood with coaxial rest of way to houses Fiber to the Curb: Fiber goes into neighborhood and is buried at curb (closer to homes) Hybrid Fiber Coax (HFC) and Fiber-to-the-Curb (FTTC) 31 Figure 9-24

31 Internet Access Technologies Comparisons Differences and similarities between cable Internet, DSL, analog modems Name Analog Circuit DSL Cable Physical 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 Internet Access Link Comparison Points 32 Table 9-3

32 Internet Access Technologies: Wireless 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 Wireless WAN Examples 33 Figure 9-26

33 34 Short Break Take 10

34 35 IPv4 Addressing Review 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

35 IP Address Assignment 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 worldwide regional organizations to Name Locations Served manage address AfriNIC Africa APNIC Asia Pacific assignment process Regional Internet Registries (RIRs) ARIN LACNIC RIPE NCC 36 North America Latin America, Caribbean Europe, Middle East, Central Asia Table 9-4

36 IPv4 Address Assignment Example 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 IANA Assigned Classful IP Network Numbers 37 Figure 9-29

37 IP Address Assignment Rules IANA IP network assignments followed these general rules: 1. Only assign network IDs not yet assigned to any other enterprise 2. Assign class of network just large enough to meet need of enterprise Enterprises Subnet their One Classful IP Network 38 Figure 9-30

38 IP Address Assignment Rules At end of process, each enterprise had public address that fell into class A, B, or C 1. IP address from public network could be used to send packets to any other network in Internet Enterprises Subnet their One Classful IP Network 39 Figure 9-30

39 WAN IP Routing Protocol: BGP Border Gateway Protocol (BGP): Internet IP routing protocol Prefers routes through less expensive links Creates large routing tables BGP: Choosing Routes (Indirectly) Based on Business Rules 40 Figure 9-32

40 WAN IP Routing 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 Scale of Internet Routing Tables: Large Enterprise Vs. Internet Core Routers 41 Figure 9-33

41 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 WAN IP Routing Internet Routing: IP Routes to Each Classful IP Network 42 Figure 9-34

42 WAN IP Routing: Single-Homed Connection Enterprise has only one WAN link connecting to ISP Single-Homed Connection with Default Route 43 Figure 9-36

43 WAN IP Routing: Dual-Homed Connection Enterprise has two (or more) connections to Internet Gives enterprise choice of where to send Internet packets Default route might not work well in such network designs Inefficient Routes With Dual-homed Internet Connections 44 Figure 9-37

44 WAN Connection: No 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 Default Routers and Default Routes 45 Figure 9-39

45 Name Resolution with DNS Name resolution and Global DNS system: Create 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 Review: IANA Assigns IP Networks 46 Figure 9-40

46 Name Resolution with DNS 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 Format and Examples Using Domain Names 47 Figure 9-41

47 Name Resolution with DNS 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 entity can use it IANA/Others Approve Subdomain Registrations 48 Figure 9-42

48 Name Resolution with DNS 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 IANA/Others Approve Subdomain Registrations 49 Figure 9-43

49 Name Resolution with DNS Example, Part 1 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 Finding the Right DNS Server for a Domain Name in Another Company 50 Figure 9-45

50 Name Resolution with DNS Example, Part 2 At this point, client does not yet know s IP address Step 5: Server sends name resolution request to DNS for subdomain server ent-1.com Step 6: DNS server ent-1.com knows name so replies with IP address Step 7: DNS server replies to Client A with IP address of so Client can now send packet with correct IP address on it Getting a Response from the Authoritative DNS Server for Ent-1.com 51 Figure 9-46

51 Scarcity of 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 Class Number of Networks Size (Number of Host Addresses) A (>16,000,000) B 16, (>65,000) C 2,097, (254) Number and Sizes of Classful IP Networks 52 Table 9-4

52 Scarcity of IPv4 Addresses Graph: Number of estimated Internet hosts Data derived primarily from RFC 1296, which collected growth data in part because of IP address exhaustion problem Approximate Number of Hosts Connected to the Internet, Figure 9-48

53 Scarcity of IPv4 Addresses Solution: CIDR 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) IANA Assigns to ISP; ISP Assigns Smaller CIDR Block to Customer 54 Figure 9-49

54 Scarcity of IPv4 Addresses Solution: CIDR 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 CIDR Address Assignment Creates Larger Routing Tables 55 Figure 9-50

55 Scarcity of IPv4 Addresses Solution: CIDR 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 customers Administrative process allows routers to create aggregate routes for original large blocks, rather than separate routes for each individual smaller block Figure

56 Scarcity of IPv4 Addresses Solution: Private IPs 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. Class Number of Networks Network IDs A B C 256 All that begin ( , , , and so on, through ) Private IP Networks 57 Table 9-5

57 Scarcity of IPv4 Addresses Solution: NAT Network Address Translation (NAT): Way to translate multiple PRIVATE addresses to single PUBLIC address for Internet access Hosts with Public IP Addresses Connected to Servers in the Internet 58 Figure 9-52

58 Scarcity of IPv4 Addresses Solution: NAT 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 ( ) NAT Function on a Router 59 Figure 9-54

59 Scarcity of IPv4 Addresses Solution: NAT Example using private and public IP addresses Three separate enterprises use PRIVATE networks based on Each company uses different PUBLIC IP address block to access Internet Three Enterprises Networks, Each Using Private Network Figure 9-55

60 Scarcity of IPv4 Addresses Solution: NAT 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 NAT Translating the Source Address in Packet from Inside to Outside 61 Figure 9-56

61 Scarcity of IPv4 Addresses Solution: NAT NAT example: Server replies to host Packet comes into NAT router with IP address of Step 6: Router consults its NAT table to translate packet s address to Client A s IP address ( ) Step 7: Router forwards packet to Client A NAT Translating the Destination Address in Packet from Outside to Inside 62 Figure 9-57

62 Scarcity of IPv4 Addresses Solution: NAT 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) Public and Private IP Addresses in the Enterprise 63 Figure 9-58

63 SOHO Address Assignment Small Office/Home Office (SOHO) address assignment: Most connections to Internet use small, consumer-grade routers that typically combine many functions into one device Various Roles of Consumer Router 64 Figure 9-59

64 SOHO Address Assignment Example SOHO address assignment User can change router defaults or use directly out of box as is Default Settings on a Consumer-Grade Integrated Router 65 Figure 9-60

65 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. 66

66 67 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.

67 68 Summary - This Chapter Compared and contrasted the public IP address assignment process that was used before IP address exhaustion, and after the introduction of CIDR. 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.

68 Questions? Comments? 69