【導(dǎo)讀】both.WANistheInter.puter,workdevices).Maintopologies:Bus,Ring,Star,andMesh. Bustopology

　　

【正文】 Class Default sub Mask No. of possible Networks No. of possible Hosts A 127 16Millions B 16,000 65,000 C 2 Million 254 Understanding IP Addresses and How They Are Used (cont’d.) ? Public IP addresses: available to the Inter ? Private IP addresses: used on private intras – Use router with NAT redirection for Inter access – IEEE remendations ? through ? through ? through A+ Guide to Managing and Maintaining Your PC, 7e 67 Table 176 Reserved IP addresses Network+ Guide to Networks, 5th Edition 68 Subting ? Separates work – Multiple logically defined segments (subs) ? Geographic locations, departmental boundaries, technology types ? Sub traffic separated from other sub traffic ? Reasons to separate traffic – Enhance security – Improve performance – Simplify troubleshooting Network+ Guide to Networks, 5th Edition 69 Classful Addressing in IPv4 ? First, simplest IPv4 addressing type ? Adheres to work class distinctions ? Recognizes Class A, B, C addresses Figure 48 IP addresses and their classes Network+ Guide to Networks, 5th Edition 70 Classful Addressing in IPv4 (cont’d.) ? Network information (work ID) – First 8 bits in Class A address – First 16 bits in Class B address – First 24 bits in a Class C address ? Host information – Last 24 bits in Class A address – Last 16 bits in Class B address – Last 8 bits in Class C address Network+ Guide to Networks, 5th Edition 71 Classful Addressing in IPv4 (cont’d.) Figure 101 Example IPv4 addresses with classful addressing Network+ Guide to Networks, 5th Edition 72 Classful Addressing in IPv4 (cont’d.) ? Drawbacks – Fixed work ID size limits number of work hosts – Difficult to separate traffic from various parts of a work Network+ Guide to Networks, 5th Edition 73 IPv4 Sub Masks ? Identifies how work subdivided ? Indicates where work information located ? Sub mask bits – 1: corresponding IPv4 address bits contain work information – 0: corresponding IPv4 address bits contain host information Network+ Guide to Networks, 5th Edition 74 IPv4 Sub Masks (cont’d.) ? Network class – Associated with default sub mask Table 101 Default IPv4 sub masks Network+ Guide to Networks, 5th Edition 75 IPv4 Sub Masks (cont’d.) ? ANDing – Combining bits ? Bit value of 1 plus another bit value of 1 results in 1 ? Bit value of 0 plus any other bit results in 0 – ANDing logic ? 1: “true”, 0: “false Table 102 ANDing Network+ Guide to Networks, 5th Edition 76 IPv4 Sub Masks (cont’d.) ? ANDing example – Address’s fourth octet ? Any bination of 1s and 0s ? Results in work ID fourth octet of 0s Figure 102 Example of calculating a host’s work ID Network+ Guide to Networks, 5th Edition 77 Reserved Addresses ? Cannot be assigned to node work interface。 used as sub masks ? Network ID – Bits available for host information set to 0 – Classful IPv4 addressing work ID ends with 0 octet – Subting allows work ID with other decimal values in last octet(s) ? Broadcast address – Octet(s) representing host information equal all 1s – Decimal notation: 255 Network+ Guide to Networks, 5th Edition 78 IPv4 Subting Techniques ? Subting breaks classful IPv4 addressing rules – IP address bits representing host information change to represent work information ? Reduce usable host addresses per sub ? Hosts, subs available after subting related to host information bits borrowed – For example if you want to have 8 works with 32 hosts then. By default on a class C work you will have 256 hosts with a sub mask of or . Network+ Guide to Networks, 5th Edition 79 IPv4 Subting Techniques ? To get closer to the number of hosts you need, say 32 hosts you need to extend your work bits (. 1) to the host bits (.) – Now, 32 is 25 which means you need only 5 bits as hosts and 3 bits (. 83) as work like the ff: – N H – That means you have 23 or 8 works and 25 or 32 hosts. – And you sub mask is now Network+ Guide to Networks, 5th Edition 80 IPv4 Subting Techniques (cont’d.) ? Class C work – Fewer subs than Class B – Less hosts per sub than Class B Sub mask No. of Networks No. of Hosts No. of Effective Hosts 4 64 62 8 32 30 16 16 14 32 8 6 64 4 2 Network+ Guide to Networks, 5th Edition 81 Example 32 hosts at range Network IP Address Range Sub Address Broadcast Address Effective Hosts 1 – – 2 – – 3 – – 4 – – 5 – – 6 – – 7 – – 8 – – Network+ Guide to Networks, 5th Edition 82 Calculating IPv4 Subs (cont’d.) ? Class A, Class B, and Class C works – Can be subted ? Each class has different number of host information bits usable for sub information ? Varies depending on work class and the way subting is used ? LAN subting – LAN’s devices interpret device subting information – External routers ? Need work portion of device IP address Network+ Guide to Networks, 5th Edition 83 Figure 103 A router connecting several subs Activity on Subting ? Imagine you are the Network administrator in an anization and you have 4 Departments and each department has a maximum of 60 puters what would be the range of IP addresses that could be used for each subwork and what would be its corresponding sub mask? ? Refer to slide 7881 as reference for your format for your answer. 84 Network+ Guide to Networks, 5th Edition 85 CIDR (Classless Interdomain Routing) ? Also called classless routing or superting ? Not exclusive of subting – Provides additional ways of arranging work and host information in an IP address – Conventional work class distinctions do not exist ? Exam