NT1210. Final Exam Review 8 to 10

Transcription

1 NT1210 Final Exam Review 8 to 10

2 Introducing the Internet Protocol (IP) TCP/IP Model review: Layers 1 and 2 Protocols Example LAN/WAN Standards and Types in the TCP/IP Model 2 Figure 8-1

3 Introducing the Internet Protocol (IP) TCP/IP Model review: Upper layers define non-physical (logical) networking functions Various Perspectives on the TCP/IP Model and Roles 3 Figure 8-2

4 4 Introducing the Internet Protocol (IP) Network Layer protocols IP: Most important protocol defined by Network layer Almost every computing device on planet communicates, and most use IP to do so Network layer also defines other protocols

5 Introducing the Internet Protocol (IP) Network Layer protocols: Part 1 Name Full Name Comments ICMP ARP DHCP DNS Internetwork Control Message Protocol Address Resolution Protocol Dynamic Host Configuration Protocol Domain Name System/Service Messages that hosts and routers use to manage and control packet forwarding process; used by ping command Used by LAN hosts to dynamically learn another LAN host s MAC address Used by host to dynamically learn IP address (and other information) it can use Allows hosts to use names instead of IP address; needs DNS server to translate name into corresponding IP address (required by IP routing process) Other TCP/IP Network Layer Protocols 5 Table 8-1

6 Introducing the Internet Protocol (IP) Network Layer protocols: Part 2 Name Full Name Comments RIP EIGRP OSPF Routing Information Protocol Enhanced Interior Gateway Routing Protocol Open Shortest Path First Application that runs on routers so that routers dynamically learn IP routing tables (used to route IP packets correctly); open standard protocol defined in RFC 2453 Proprietary routing protocol owned by Cisco Systems Open source routing protocol defined in RFC 2328 Other TCP/IP Network Layer Protocols 6 Table 8-1

7 7 Introducing the Internet Protocol (IP) IPv6: Next generation of IP addressing. Needed because IPv4 addresses exhausted. 128-bit long addresses: or 3.4x1038 or over 340 undecillion IPs, that s 340 with 36 zero s after it. Customer usually gets /64 subnet, which yields 4 billion times IPs available in all of IPv4. Comparison: Number of IPv4 addresses equal to weight of cat; number of IPv6 addresses equal to weight of Earth and provides enough IP addresses for every grain of sand on every beach on earth.

8 Introducing the Internet Protocol (IP) Migration to IPv6 has taken over decade and still in process. IPv6 originally defined back in mid-1990s. June 6, 2012 Was the scheduled IPv6 Day, official worldwide switch over day, moved up to February IPv4 Vs. IPv6 Timeline 8 Figure 8-3

9 Introducing the Internet Protocol (IP) IP defines many functions that work together with one ultimate goal: To send data from one host to another host through any TCP/IP network. Most important functions include: Creating end-to-end physical paths through TCP/IP network by interconnecting physical networks (LANs and WANs) using routers Identifying individual hosts and groups of hosts using IP addressing Routing (forwarding) IP packets to correct destination host Example of a Post Office Sorting a Letter Sent to Hollywood, California 9 Figure 8-4

10 Introducing the Internet Protocol (IP) IP is like Post Office Example of a Post Office Sorting a Letter Sent to Hollywood, California 10 Figure 8-4

11 Introducing the Internet Protocol (IP) Routers in IP network: Interconnect LANs and WANs via physical connectors called interfaces Example: Cisco 1841 router with two built-in Gigabit Ethernet LAN interfaces that use RJ-45 connectors Enterprise Class Router, LAN Interfaces, and WAN Interfaces 11 Figure 8-5

12 Introducing the Internet Protocol (IP) IP interconnects LANs and WANs Interconnected LANs and WANs: Redundancy, but No LAN/WAN Detail 12 Figure 8-7

13 Introducing the Internet Protocol (IP) IPv4 Addresses 32 bits Expressed in binary and dotted decimal forms Source and destination IP addresses included in 20-byte IP header added to all IP packets IPv4 Header Format and Fields 13 Figure 8-8

14 Introducing the Internet Protocol (IP) Converting binary IP address to dotted decimal 1. Separate 32 bits into 4 groups of 8 bits each 2. Do binary-to-decimal conversion of each 8-bit number (each decimal value between 0 and 255) 3. Put period (dot) between each decimal number Generic View of Converting from Binary IP Address to DDN Format 14 Figure 8-9

15 Introducing the Internet Protocol (IP) Example: Converting binary IP address to dotted decimal Converting Binary IP Address to DDN Figure 8-10

16 Introducing the Internet Protocol (IP): Routing Routing IP Packets from Source to Destination IP addressing groups addresses into networks All addresses with same value in first parts of addresses considered to be in one network Example: All addresses that begin with 11, 12, 13, 14, or 15 in that particular network Example IP Address Groupings: All with the Same First Octet in the Same Group 16 Figure 8-11

17 Introducing the Internet Protocol (IP): Routing IP routing example with routing tables: PC11 in left LAN sends IP packet to address (LAN on upper right) Example IP Address Groupings: All with the Same First Octet in the Same Group 17 Figure 8-12

18 Introducing the Internet Protocol (IP): Routing Routers build routing tables in two ways Static configuration: Routes entered manually and do not change Dynamic routing protocol: Application router uses to automatically learn new routes from other routers Routing Protocols Advertising All Addresses that Begin with 12 as One Route 18 Figure 8-13

19 Introducing the Internet Protocol (IP): Other Protocols Domain Name System/Service (DNS): Mapping names to IP addresses Users use names; IP routing uses numbers DNS translates name into corresponding IP address DNS client sends DNS Request message DNS server returns DNS Reply DNS Name Resolution Request, Reply, and Packet to Server1 IP Address 19 Figure 8-14

20 Introducing the Internet Protocol (IP): Other Protocols Layer 3 - Network IP with its Support Protocols 20 Figure 8-15

21 IP Addressing on User LANs: Network Settings Locations Need IP addresses Each LAN and WAN interface on hosts and routers need IP address to communicate IP Addresses Used on Every LAN/WAN Interface 21 Figure 8-17

22 IP Addressing on User LANs: Network Settings IP Address grouping: Allows IP routing to work better Routers list one number to represent each network (address group) in routing tables IP Address Groupings: IP Networks 22 Figure 8-18

23 IP Addressing on User LANs: Network Settings Original IPv4 RFC defined way to group IPv4 addresses using IP address classes (classful IP addressing) Every possible IPv4 address falls into class First Octet Class Purpose 0 A Reserved A Unicast addresses, in class A networks 127 A Reserved for loopback testing B Unicast addresses, in class B networks C Unicast addresses, in class C networks D Multicast addresses; not used as unicast IP addresses E Experimental; not used as unicast IP addresses Summary of IPv4 Address Classes Based on First Octet Values 23 Table 8-2

24 IP Addressing on User LANs: Network Settings Class A includes lower half of IPv4 address space: All IPv4 address that begin with first octet between 0 and 127 Network ID Class A IP Network Concept Size (Number of Addresses) All addresses with a first octet equal to 1 > 16,000, All addresses with a first octet equal to 2 > 16,000, All addresses with a first octet equal to 3 > 16,000, All addresses with a first octet equal to 4 > 16,000,000 Etc. > 16,000, All addresses with a first octet equal to 126 > 16,000,000 Example Class A Networks 24 Table 8-3

25 IP Addressing on User LANs: Network Settings Class B includes ¼ of IPv4 address space with first octet value from Includes medium number (2 16 ) of medium sized IP networks for approximately 65,000 hosts per network Network ID Concept Size (Number of Addresses) All with a first two octets equal to > 65, All with a first two octets equal to > 65, All with a first two octets equal to > 65, All with a first two octets equal to > 65, All with a first two octets equal to > 65, All with a first two octets equal to > 65,000 Example Class B Networks 25 Table 8-4

26 IP Addressing on User LANs: Network Settings Class C includes 1/8 th of IPv4 address space with first octet between 192 and 223 Large number of small IP networks: over 2,000,000 IP networks, each with 256 IP addresses each Network ID Concept Size (Number of Addresses) All with a first three octets equal to All with a first three octets equal to All with a first three octets equal to All with a first three octets equal to All with a first three octets equal to All with a first three octets equal to Example Class C Networks 26 Table 8-5

27 IP Addressing on User LANs: Network Settings LAN IP address classes summary Summary of How Class Rules Break Down the IPv4 Address Space 27 Figure 8-20

28 IP Addressing on User LANs: Network Settings Private addresses: Classful IP networks reserved for enterprises to use in their network designs Can only be used on local LAN; can t be routed through WAN (non-routable) Not regulated by agencies such as ARIN or ICANN Network ID Concept 10.x.x.x x.x x.x x.x Class A Private IP addressing space Class B Private IP addressing space Class C Private IP addressing space Size (Number of Addresses) Over 16,000,000 networks of over 16,000,000 IPs each Over 65,000 networks of over >65,000 IPs each Over 65,000 networks of 256 IPs each 28

29 IP Addressing on User LANs: Network Settings Static IP address assignment: Manually configured Static IP Address Assignment on Mac OS X 29 Figure 8-21

30 IP Addressing on User LANs: Network Settings Most host OS s allow static configuration of several network settings Host IP Settings 30 Figure 8-22

31 IP Addressing on User LANs: Network Settings Dynamic Host Configuration Protocol (DHCP) defines way hosts can lease IP address from DHCP network server so does not have to be configured statically Operates on client-server concept DHCP protocol defined by set of RFCs Sample Network for DHCP Discussions 31 Figure 8-23

32 IP Addressing on User LANs: Network Settings Example: IP address assignment design using both DHCP and statically assigned addresses Location Type Range Atlanta LAN Static DHCP Boston LAN Static DHCP San Fran LAN Static DHCP Address Planning: Some Static, Some DHCP, for Every LAN 32 Table 8-6

33 IP Addressing on User LANs: Network Settings Once DHCP server exists in network and has been configured with set of IP addresses to lease, DHCP clients can request IP addresses DHCP Lease Process between a DHCP Client and Server 33 Figure 8-24

34 IP Addressing on User LANs: Network Settings User can see results of DHCP process from computer DHCP Client Configuration on Mac OS X 34 Figure 8-25

35 IP Addressing on User LANs: Network Settings DHCP example: Crossing networks to access DHCP server Remote DHCP Client in Boston 35 Figure 8-26

36 IP Routing with Focus on Layer 3 IP defines how to route packets across TCP/IP network Some routing tasks must use logic from lower two layers because Network layer (3) cannot physically send bits Network layer relies on Layers 1 and 2 logic for this IP Routing Perspective, While Ignoring LAN/WAN Details 36 Figure 8-27

37 37 IP Routing with Focus on Layer 3 Router must have IP routing table with useful entries to route IP packets. Routing table may list multiple routes. Each IP route identifies network, as well as other information about how to send packets to that network. Routers look at incoming packet s destination IP address and compare it to list of network IDs in its routing table to determine where to send packet to destination.

38 IP Routing with Focus on Layer 3 Finding a classful network ID based on IP address Five Classful Networks in a Small Corporate Network 38 Figure 8-28

39 IP Routing with Focus on Layer 3 Each route in routing table lists: Information about how to match IP packets Forwarding instructions that tell router where to forward packets to (e.g., next router) Example: R1 s IP routing table shows five network IDs so it knows routes to all five networks R1 Routing Table with Routes for Five Classful Networks 39 Figure 8-29

40 IP Routing with Focus on Layer 3 Router compares incoming IP packet s destination address to information in its routing tables to find best route to destination How Router R1 Uses its IP Routing Table: Match and Forward 40 Figure 8-30

41 IP Routing with Focus on Layer 3 Routing from End-to-End: Multiple Cooperative Routing Decisions 41 Figure 8-31

42 IP Routing with Focus on Layer 3: Subnetting Classful IP networks and wasted IP addresses Subnetting: Process of subdividing network to create smaller groups of consecutive IP addresses Subnets (subdivided networks): Smaller groups of addresses Numbers of Classful Networks, and Their Sizes 42 Figure 8-32

43 IP Routing with Focus on Layer 3: Subnetting Example: Several subnets created by subnetting network Each subnet has subnet/network ID Subdividing (Subnetting) Class A Network Figure 8-33

44 IP Routing with Focus on Layer 3: Subnetting Example continued: IP addresses and networks replaced with five subnets of network Sample Corporate Network Using Subnets of Network Figure 8-34

45 IP Routing with Focus on Layer 3: Subnetting Subnet mask: Shows how much of IP address for each device is in common to all IPs in subnet Example (/24): First three octets (first 24 bits) must be equal for all subnets in network PC11 sends packet to PC21 (destination IP address ) R1 will have route for PC21 s subnet (network ID ) Routing Logic with Subnets and Masks 45 Figure 8-35

46 IP Routing with Focus on Layer 3: Subnetting Classful networks have default subnet mask based on each class Class A: (8 bits) Class B: (16 bits) Class C: (24 bits) If subnet mask anything other than default, then subnetting being used Routing Logic with Subnets and Masks 46 Figure 8-35

47 47 IP Routing with Focus on Layer 3: Subnetting How to calculate subnets 1. Determine network class (A, B, or C) 2. Determine EITHER number of hosts needed for each subnet OR how many subnets needed 3. Determine how many bits needed to provide correct number of hosts/subnets; last subnet is NOT usable 4. Calculate IPs for each subnet; first IP identifies subnet (Network ID) and last IP identifies broadcast address 5. Determine subnet mask (total number of bits for network/subnet ID)

48 48 IP Routing with Focus on Layer 3: Subnetting Example: Calculating subnets for network Class: C Number of subnets needed: 14 Number of bits needed to supply 14 subnets: 3 Number of bits left to determine number of IPs per subnet: 5 (results in 32 IPs per subnet) Subnet mask: (default 16 bits + 3 more bits for subnetting = 19 bits)

49 49 IP Routing with Focus on Layer 3: Subnetting Subnet No. Network ID Host Range IPs Broadcast IP

50 IP Routing with Focus on Layer 3: Subnetting What happens when PC11 sends IP packet to PC12: Same subnet 1. PC11 determines its own IP address and subnet mask ( and ) 2. PC11 decides determines destination is in same subnet 3. PC11 sends packet directly to PC12 without going through router R1 IP Host Routing Logic: Local Destination 50 Figure 8-36

51 IP Routing with Focus on Layer 3: Subnetting What happens when PC11 sends IP packet to PC12: Different subnets 1. Host s default gateway (default router) setting tells it where to send packets when they have destination address in different subnet 2. Default gateway tells host IP address of router attached to its LAN 3. Router then consults its routing table and determines how to deliver packet IP Host Routing Logic: Remote Destination 51 Figure 8-37

52 IP Routing with Layer 1, 2, and 3 Interactions Encapsulation: Action taken by lower layer when it takes data from higher layer and adds header (and sometimes trailer) to higher layer s data Example: PC11 opened web browser and tried to connect to URL at web server: PC11 creating bits it uses to send to server S1 (web server) Encapsulation Review: Application, Transport, and Network Layers 52 Figure 8-38

53 IP Routing with Layer 1, 2, and 3 Interactions PC encapsulating IP packet into Ethernet frame (step 4) Sending bits over LAN cable into network (step 5) Encapsulation Review: Data Link Layer 53 Figure 8-39

54 IP Routing with Layer 1, 2, and 3 Interactions De-encapsulation: On the destination side De-encapsulation on a Receiving Host (S1) 54 Figure 8-40

55 IP Routing with Layer 1, 2, and 3 Interactions Addressing frames and packets when crossing SAME subnet: Both MAC and IP addresses in Ethernet frame and encapsulated IP packet IP and Ethernet Addresses, PC11 to server S1, Same Subnet 55 Figure 8-42

56 IP Routing with Layer 1, 2, and 3 Interactions To learn destination MAC address, sending device uses Address Resolution Protocol (ARP) and info in ARP table Address Short Answer Long Answer Given to Ethernet NIC by manufacturer; sending Source MAC On NIC host can find MAC on NIC hardware. Source IP Configuration Either through static configuration or DHCP Destination MAC Destination IP ARP User From its ARP table, or if not found, by using ARP protocol and sending ARP Request and waiting for ARP Reply from destination Either typed or clicked by user How a Sending IP Host Knows What Addresses to Use 56 Table 8-9

57 IP Routing with Layer 1, 2, and 3 Interactions Discovering MAC addresses using ARP: ARP Request and ARP Reply ARP Request (ARP Broadcast): Sending device queries for MAC address of destination device; sends Request as broadcast to all other devices on subnet Example: PC11 wants to send packet to server S1 (in same subnet) but does not know S1 s MAC address; PC11 sends ARP Request to all devices on subnet ARP Request (Broadcast) 57 Figure 8-43

58 IP Routing with Layer 1, 2, and 3 Interactions ARP Reply: Lists IP address ARP Request asked about with corresponding MAC address of that host Example: ARP Reply that server S1 makes in response to PC11 s ARP Request ARP Reply is unicast since ARP Request generated from one particular device ARP Reply (Unicast) 58 Figure 8-44

59 IP Routing with Layer 1, 2, and 3 Interactions Routing data between different subnets IP packets in network act like person traveling to destination, using all forms of transportation; packet goes from end-to-end Data Link frames act like individual vehicles used for only part of trip (e.g., just train); frames never leave their own LAN/WAN Example, IP Packet End-to-End, Data Link Heads Stay on LAN or WAN 59 Figure 8-45

60 IP Routing with Layer 1, 2, and 3 Interactions Addressing frames and packets when crossing subnets example: PC11 ( ) sends IP packet to PC21 ( ) Hosts sit on different LANs (may also be in different subnets) IP Addresses Stay the Same Through End-to-End Path 60 Figure 8-46

61 IP Routing with Layer 1, 2, and 3 Interactions Example: PC11 sends IP packet to PC21 PC11 s logic tells it to send packet to default router because destination is in different network or subnet PC11 encapsulates packet inside Ethernet frame with destination MAC address R1 Ethernet Frames Use MAC on that LAN (Only) 61 Figure 8-47

62 IP Routing with Layer 1, 2, and 3 Interactions Removing/adding Data Link headers: Router removes IP packet from incoming Data Link frame (deencapsulation) and then adds new Data Link header and trailer before sending packet (encapsulation) Steps router goes through: 1. De-encapsulates IP packet from inside Data Link frame 2. Makes routing decision using packet s destination IP address and its own IP routing table, identifying correct outgoing interface 3. Encapsulates packet into new Data Link frame that works on outgoing interface 4. Sends packet through outgoing interface to destination Routers Discard Old and Add New Data Link Framing 62 Figure 8-48

63 IP Routing with Layer 1, 2, and 3 Interactions Example: When R1 receives packet destined to subnet on R2 Routers Discard Old and Add New Data Link Framing 63 Figure 8-48

64 IP Routing with Layer 1, 2, and 3 Interactions Using ARP with routers: R2 needs to deliver IP packet to host PC21 1. R2 builds Ethernet header with PC21 s MAC address as destination 2. If R2 does not know PC21 s MAC address (i.e., it is not in its ARP table), R2 uses ARP to learn MAC address 3. When R2 receives ARP Reply with PC21 s MAC address, sends frame Example of Router R2 Using ARP to Learn a Local Host s MAC Address 64 Figure 8-49

65 The Internet as a Network of Networks Internet Access Links from TCP/IP Networks, Large and Small 65 Figure 9-1

66 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 66 Figure 9-2

67 The Internet as a Network of Networks Connecting enterprises Typical Organizations Whose TCP/IP Networks Connect to the Internet 67 Figure 9-3

68 The Internet as a Network of Networks Connecting to Internet edge: Part of Internet topology between ISP and customer (sits at edge of both networks) Comparing an Enterprise and ISP Network 68 Figure 9-4

69 The Internet as a Network of Networks From network layer perspective: Internet access link acts like any other WAN link between routers T3 Serial Link Connection to the Internet 69 Figure 9-5

70 The Internet as a Network of Networks 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 An Example Case of Using an Enterprise Firewall and IPS 70 Figure 9-6

71 The Internet as a Network of Networks 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 Example: Two attempts from users in Internet to connect to two different servers in enterprise Firewall Allowing Connections to Public Web Servers Only 71 Figure 9-7

72 The Internet as a Network of Networks 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 72 Figure 9-8

73 The Internet as a Network of Networks 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 ISP Point-of-Presence (PoP) Concept with Customer Access 73 Figure 9-9

74 The Internet as a Network of Networks Example: Typical PoP with access routes using direct link to distribution router which connects to rest of ISP s network Example of Dividing Responsibilities Inside an ISP PoP 74 Figure 9-10

75 The Internet as a Network of Networks 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) Connecting All ISP PoP Routers to Create an ISP TCP/IP Network 75 Figure 9-11

76 The Internet as a Network of Networks 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 76 Figure 9-12

77 The Internet as a Network of Networks 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 77 Figure 9-13

78 The Internet as a Network of Networks Other providers of Internet services: Companies who provide services available through Internet Web hosting Search engines Social media Cloud services Other Service Providers Connected to the Internet 78 Figure 9-14

79 79 The Internet as a Network of Networks 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

80 The Internet as a Network of Networks Web hosting 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 80 Figure 9-15

81 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 Two ISP Customers Using Analog Modems and Analog Phone Lines 81 Figure 9-16

82 Internet Access Technologies 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 Role of PPP on a Analog Dial-up Circuit to an ISP 82 Figure 9-17

83 83 Internet Access Technologies 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

84 Internet Access Technologies Using analog phone lines for Internet access Name Physical link Always on? Allows voice at same time over same medium? Asymmetric? (Faster downlink possible?) Approximate real-life downlink speeds Analog Modem Telco local loop No No No 56 Kbps Comparison Points: Analog Modem 84 Table 9-1

85 Internet Access Technologies 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 DSL Using Multiple Frequencies over a Single Local Loop 85 Figure 9-18

86 Internet Access Technologies Line splitter allows both analog phone and DSL modem to connect to same phone line and transmit simultaneously Home Cabling and Devices for DSL 86 Figure 9-19

87 Internet Access Technologies 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 87 Figure 9-20

88 Internet Access Technologies 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 88 Figure 9-21

89 Internet Access Technologies Differences and similarities between analog and DSL modems 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 89 Table 9-2

90 Internet Access Technologies 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 Cable Internet Using Multiple Frequencies over a Single Circuit on Co-axial Cable 90 Figure 9-22

91 Internet Access Technologies Cable modem example: Cable modem feed comes from same cable as TV connection Home Cabling and Devices for Cable Internet 91 Figure 9-23

92 Internet Access Technologies 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) Hybrid Fiber Coax (HFC) and Fiber-to-the-Curb (FTTC) 92 Figure 9-24

93 Internet Access Technologies 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 93 Figure 9-25

94 Internet Access Technologies 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 94 Table 9-3

95 Internet Access Technologies 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 95 Figure 9-26

96 Internet Access Technologies Consumer Internet-access technologies use cabling already in most homes; makes it inexpensive and affordable Enterprise WAN Options Used as Internet Access Technologies 96 Figure 9-27

97 97 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

98 Network Layer Concepts Before Scarce IP Addresses Many different organizations (typically part of some notfor-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 Name AfriNIC APNIC ARIN LACNIC RIPE NCC Locations Served Africa Asia Pacific North America Latin America, Caribbean Europe, Middle East, Central Asia Regional Internet Registries (RIRs) 98 Table 9-4

99 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 IANA Assigned Classful IP Network Numbers 99 Figure 9-29

100 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 enterprise 2. 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 Enterprises Subnet their One Classful IP Network 100 Figure 9-30

101 Network Layer Concepts Before Scarce IP Addresses Example of SOHO address assignment in early days: ISP1 reserved class C network When PC2 and PC3 connect to ISP, they are given addresses by ISP1 router Assigning IP Addresses to SOHO PCs 101 Figure 9-31

102 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 BGP: Choosing Routes (Indirectly) Based on Business Rules 102 Figure 9-32

103 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 Scale of Internet Routing Tables: Large Enterprise Vs. Internet Core Routers 103 Figure 9-33

104 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 Internet Routing: IP Routes to Each Classful IP Network 104 Figure 9-34

105 Network Layer Concepts Before Scarce IP Addresses Routers receive packets and then send them to next router IP Forwarding (Routing) on Several ISP Routers 105 Figure 9-35

106 Network Layer Concepts Before Scarce IP Addresses Single-homed connection means that enterprise has only one WAN link connecting to ISP Single-Homed Connection with Default Route 106 Figure 9-36

107 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 such network designs Inefficient Routes With Dual-homed Internet Connections 107 Figure 9-37

108 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 and , and routers R1 and R2 view route to Internet through ISP2 as better route Partial BGP Updates 108 Figure 9-38

109 Network Layer Concepts Before Scarce IP Addresses 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 Default Routers and Default Routes 109 Figure 9-39

110 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 Review: IANA Assigns IP Networks 110 Figure 9-40

111 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 Format and Examples Using Domain Names 111 Figure 9-41

112 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 entity can use it IANA/Others Approve Subdomain Registrations 112 Figure 9-42

113 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 IANA/Others Approve Subdomain Registrations 113 Figure 9-43

114 Network Layer Concepts Before Scarce IP Addresses 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 DNS Servers and Distributed Server Configurations 114 Figure 9-44

115 Network Layer Concepts Before Scarce IP Addresses 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 115 Figure 9-45

116 Network Layer Concepts Before Scarce IP Addresses 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 116 Figure 9-46

117 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 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 117 Table 9-4

118 Network Layer Concepts with Scarce IPv4 Addresses Example of IP address assignment: Enterprise asks for Class B network from IANA IANA grants network Internet routers update routing tables with routes for ; entire class B network must be in one place Wasted IP Addresses: Got 65,000, Need Figure 9-47

119 Network Layer Concepts with Scarce 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

120 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) IANA Assigns to ISP; ISP Assigns Smaller CIDR Block to Customer 120 Figure 9-49

121 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 CIDR Address Assignment Creates Larger Routing Tables 121 Figure 9-50

122 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 CIDR Route Aggregation Keeps Other ISP Routing Tables Smaller 122 Figure 9-51

123 Network Layer Concepts with Scarce IPv4 Addresses 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 123 Figure 9-52

124 Network Layer Concepts with Scarce IPv4 Addresses Three different connections from one host Server maps IP address for each connection One Client Host with Three Application Connections 124 Figure 9-53

125 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 ( ) NAT Function on a Router 125 Figure 9-54

126 Network Layer Concepts with Scarce IPv4 Addresses 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

127 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. Class Number of Networks Network IDs A B C 256 All that begin ( , , , and so on, through ) Private IP Networks 127 Table 9-5

128 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 NAT Translating the Source Address in Packet from Inside to Outside 128 Figure 9-56

129 Network Layer Concepts with Scarce IPv4 Addresses NAT example, Part 2: 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 129 Figure 9-57

130 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) Public and Private IP Addresses in the Enterprise 130 Figure 9-58

131 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 Various Roles of Consumer Router 131 Figure 9-59

132 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 ) 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 Various Roles of Consumer Router 132 Figure 9-59

133 Network Layer Concepts with Scarce IPv4 Addresses 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 133 Figure 9-60

134 Transport and Application Protocols TCP/IP Transport: TCP/IP model s two upper layers (Application and Transport) define how applications communicate and other important features of what applications can do on network Transport and Application Layers focus on hosts Scope of Impact for TCP/IP Layers 134 Figure 10-1

135 Transport and Application Protocols Host perspectives on upper layers: Upper layer protocols exist in both application and OS Application developers include Application layer protocol in application (e.g., Telnet) OS vendor includes Transport protocol inside OS (e.g., IE in Windows) Software Architecture of Application and Transport Layers 135 Figure 10-2

136 Transport and Application Protocols Serving needs of next higher Layer: On hosts, each function has needs and supplies answer to needs of other functions Example: Web browser Application needs to get web page; Application protocol takes care of it using browser application and HTTP does that by using HTTP GET command Needing and Supplying Services in TCP/IP Upper Layers 136 Figure 10-3

137 137 Transport and Application Protocols Encapsulation and headers: Application and Transport layer protocols use headers to do their work Application protocol on sending host adds Application protocol header that destination host s Application layer protocol reads Transport layer adds headers based on protocol used: TCP or UDP

138 Transport and Application Protocols UDP header format TCP header format UDP/TCP Header Reference 138 Figure 10-4,5

139 Transport and Application Protocols Sending host adds original Application and Transport layer header to data to create message; upper layer messages remain mostly unchanged as they pass through network Example: Message from web server going the web browser; message shows TCP, HTTP, Data Link, and IP headers plus data going through route from host to host Encapsulation with Web Traffic, All Layers 139 Figure 10-6

140 Transport and Application Protocols Applications and their preferred Transport protocols Some Applications Using TCP, and Some Using UDP 141 Figure 10-8

141 Transport Layer Concepts Elements of Transport Protocols Addressing Connection Establishment Connection Release Flow Control and Buffering Multiplexing Crash Recovery Needing and Supplying Services in TCP/IP Upper Layers 142 Figure 10-3

142 Transport Layer Concepts TCP: Reliable, in-order delivery Congestion control Flow control Connection setup UDP: Unreliable, unordered delivery No-frills, best-effort delivery Delay guarantees Bandwidth guarantees Needing and Supplying Services in TCP/IP Upper Layers 143 Figure 10-3

143 144 Transport Layer Concepts Connection establishment using three-way handshake CR = CONNECTION REQUEST (a) Normal operation (b) Old CONNECTION REQUEST appearing out of nowhere (c) Duplicate CONNECTION REQUEST and duplicate ACK

144 145 Transport Layer Concepts Connection release (a) Normal case of three-way handshake release (b) Error case: Final ACK lost

145 146 Transport Layer Concepts Flow control: Window can dynamically resize According to network conditions According to sender s capacity According to receiver s capacity

146 147 Transport Layer Concepts Buffering (a) Chained fixedsize buffers (b) Chained variable-sized buffers. (c) One large circular buffer per connection

147 148 Transport Layer Concepts Multiplexing Multiplexing at sender: Handles data from multiple sockets, adds transport header (later used for demultiplexing) Demultiplexing at receiver: Uses header info to deliver received segments to correct socket

148 149 Transport Layer Concepts Crash Recovery: Different combinations of client and server strategies

149 Transport Layer Port Numbers Most host OSs allow multiprocessing which allows more than one program to be active at same time Each active program gets share of CPU and RAM with all programs taking turns Transport of data packets similar Protocol identifies correct application process on destination host and uses port to identify communication session Concept of Application-to-Application Flows Between Two Apps 150 Figure 10-9

150 Transport Layer Port Numbers Port numbers identify application processes Example: 3 TCP communication sessions with TCP port numbers; Both hosts are using TCP port 1024 so have to use different TCP port numbers to identify separate communication sessions Three TCP Flows with Unique TCP Ports per Host 151 Figure 10-10

151 Transport Layer Port Numbers Port numbers need to be unique on each source host because of how TCP uses destination port number Example: Right shows destination host s TCP software; when top segment arrives (destination port 80), Host2 looks at its list of active TCP ports to find port 80 Destination Host Chooses Right Destination Application Based on Destination Port 152 Figure 10-11

152 Transport Layer Port Numbers Initializing servers with well known ports example: Two server software processes (web server and server) Web server uses HTTP (Application protocol) which uses default port of 80 server uses POP3 (Application protocol) which uses port 110 Two Servers with Well-Known Ports Open and Listening for New Connections 153 Figure 10-12

153 Transport Layer Port Numbers What happens on server when server software registered to use specific port number? Example using web server: Software uses its default setting to use port for HTTP: TCP port 80 Server Initializing Well-Known Port 80 for HTTP 154 Figure 10-13

154 Transport Layer Port Numbers Web browser software knows web servers should use port 80 by default client software knows that POP3 servers use TCP port 110 by default Clients Send TCP Segments to Correct Well-Known Port Numbers 155 Figure 10-14

155 Transport Layer Port Numbers Application Protocol Transport Protocol Port Number Description HTTP TCP 80 Used by web browsers and web servers Telnet TCP 23 Used for terminal emulation SSH TCP 22 Used for secure terminal emulation FTP TCP 20, 21 Used for file transfer DNS UDP 53 Used for name-to-ip resolution SMTP TCP 25 Used to send POP3 TCP 110 Used to receive IMAP TCP 143 Used to receive SSL TCP 443 Used to encrypt data for secure transactions SNMP UDP 161, 162 Used to manage TCP/IP networks Common Application Protocols and Their Well-known Port Numbers 156 Table 10-1

156 Transport Layer Port Numbers Dynamically allocated port Client Initializing a Dynamic Port Number Assigned by OS (TCP) 157 Figure 10-15

157 Transport Layer Port Numbers Dynamic port assignment on client computer when user opens web browser Client Initializing a Dynamic Port Number Assigned by OS (TCP) 158 Figure 10-16

158 Transport Layer Port Numbers IANA regulates range of numbers for well known ports, dynamic ports, and registered ports Ranges apply to both TCP and UDP Type Port Number Range Well-known Registered 1,024 49,151 Dynamic 49,153 65,535 Well-known, Registered, and Dynamic Port Numbers 159 Table 10-2

159 Transport Layer Port Numbers To deliver data, TCP encapsulates data inside TCP segment Segment lists source port and destination port To begin communication process, servers initialize and start listening for new sessions from clients and Web Servers Waiting for Flows 160 Figure 10-17

160 Transport Layer Port Numbers Example: Client opens web browser to connect to web server which creates multiple TCP sessions Client needs three TCP port numbers, one per session User also checks his which creates fourth TCP session Four Flows with (Dynamic) Source Ports and Well-Known Destination Ports 161 Figure 10-18

161 Transport Layer Port Numbers Four returning messages with their respective port numbers Port Numbers Reversed for TCP Segments in the Opposite Direction 162 Figure 10-19

162 Other Transport Functions: Segmentation Packets restricted for size in TCP/IP network so use segmentation to break large data packages into smaller pieces Maximum Transmission Unit (MTU): Maximum size of IP packet that can be sent out network device interface (e.g., router) Based on interface s Data Link protocol; example: Ethernet has MTU of 1500 bytes for TCP IP MTU Concept on Ethernet Links 163 Figure 10-20

163 Other Transport Functions: Segmentation IP fragmentation and TCP segmentation play important roles in TCP/IP networks TCP on sending host breaks large data chunks into smaller pieces when creating original TCP segments TCP segmentation example: Web server needs to send web object (picture.jpg) which is 14,600 bytes File size exactly 10 times MSS on server s Ethernet interface so divided into 10 segments for transport Web Server Sends Web Object; TCP Segments 164 Figure 10-21

164 Other Transport Functions: Segmentation UDP datagram: UDP messages that include UDP header and its encapsulated data UDP also needs to segment data: Limited to maximum size of each link Example: UDP datagram MTU 1472 bytes on Ethernet link UDP Datagram Maximum Data Size on Ethernet Links 165 Figure 10-22

165 166 Other Transport Functions: Connection Management TCP guarantees delivery and has error recovery built in (connection-oriented) To confirm destination received data, TCP uses acknowledgments for each segment received with no errors Example: Web server sends three TCP segments to web browser with sequence numbers (SEQ); client sends message back to server (ACK) stating all three segments received and to send next set of segments

166 Other Transport Functions: Connection Management When using TCP, sender/receiver perform handshake before exchanging data Agree to establish connection (each knowing other willing to establish connection) Agree on connection parameters TCP Sequence Numbers and Acknowledgement Concepts 167 Figure 10-23

167 168 Other Transport Functions: Connection Management Three-way handshake client state LISTEN choose init seq num, x send TCP SYN msg SYNSENT received SYNACK(x) ESTAB indicates server is live; send ACK for SYNACK; this segment may contain client-to-server data SYNbit=1, Seq=x choose init seq num, y send TCP SYNACK msg, acking SYN SYN RCVD SYNbit=1, Seq=y ACKbit=1; ACKnum=x+1 ACKbit=1, ACKnum=y+1 received ACK(y) indicates client is live server state LISTEN ESTAB

168 169 Other Transport Functions: Connection Management Congestion control: Too many sources sending too much data too fast for network to handle Different from flow control! Manifestations Lost packets (buffer overflow at routers) Long delays (queuing in router buffers)

169 170 Other Transport Functions: Connection Management UDP: Connectionless protocol Does not use acknowledgements Does not use sequencing Will not retransmit missing datagrams Considered less reliable than TCP Has much less overhead than TCP Much faster than TCP

170 171 Other Transport Functions: Error Recovery TCP error recovery uses SEQ and ACK packets 1. Data sent from source in TCP segments with sequence numbers 2. Source expects to receive ACK from destination with next sequence number 3. If source does not receive ACK with expected value or receives no ACK at all in reasonable time, retransmits TCP segments

171 Other Transport Functions: Error Recovery When receiving host gets some, but not all segments, can send back ACK but with value that tells sender to retransmit some data Example: Second TCP segment has bit errors that occurred during its trip through network so destination router discards TCP segment An Example with an Error; the Recovery Happens Later 172 Figure 10-24