Guide to TCP/IP, Third Edition. Chapter 2: IP Addressing and Related Topics

Transcription

1 Guide to TCP/IP, Third Edition Chapter 2: IP Addressing and Related Topics

2 Objectives Understand IP addressing, anatomy and structures, and addresses from a computer s point of view Recognize and describe the various IP address classes from A to E, and explain how they re composed and used Understand the nature of IP address limitations, and how techniques like Classless Inter-Domain Routing and Network Address Translation ease those limitations IP Addressing and Related Topics 2

3 Objectives (continued) Define the terms subnet and supernet, and apply your knowledge of how subnets and supernets work to solve specific network design problems Understand how public and private Internet addresses are assigned, how to obtain them, and how to use them properly Recognize the importance and value of an IP addressing scheme IP Addressing and Related Topics 3

4 IP Addressing Basics Computers deal with network addresses as bit patterns IP uses a three-part addressing scheme Symbolic Example support.dell.com Logical numeric Example Physical numeric Six-byte numeric address, burned into firmware (on a chip) by network interface manufacturers IP Addressing and Related Topics 4

5 IP Addressing Basics (continued) Address Resolution Protocol (ARP) Permits computers to translate numeric IP addresses to MAC layer addresses ReverseARP (RARP) Translates MAC layer addresses into numeric IP addresses IP Addressing and Related Topics 5

6 Anatomy of an IP Address IP addresses Dotted decimal notation Take the form n.n.n.n, where n is guaranteed to be between 0 and 255 Each number is an 8-bit number called an octet Duplication is not allowed IP Addressing and Related Topics 6

7 IP Address Classes IP addresses Subdivided into five classes: Class A to Class E For first three classes octets are divided as follows Class A n. h.h.h Class B n.n. h.h Class C n.n.n. h n = network, h = host IP Addressing and Related Topics 7

8 IP Address Classes (continued) Address Classes D and E are for special uses Class D addresses Multicast communications Class E addresses Reserved entirely for experimental use IP Addressing and Related Topics 8

9 More About Class A Addresses Class A addresses in binary form 0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb b can be 1s or 0s Reserved for special uses Addresses consisting of all 0s and all 1s Reserved for private network use Address for network 10 ( ) Reserved for loopback testing Address 127.n.n.n IP Addressing and Related Topics 9

10 IP Addressing and Related Topics 10

11 More About Class B Addresses Class B addresses take the following binary form 10bbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb b can be 1s or 0s Maximum number of usable network addresses 16,366 Maximum number of public IP addresses IP Addressing and Related Topics 11

13 More About Class C Addresses Class C addresses take the following binary form 110bbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb b can be 1s or 0s The maximum number of usable network addresses Reserved for private use 256 Class C addresses, from to IP Addressing and Related Topics 13

15 More About Address Classes D and E Class D addresses 1110bbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb b can be 1s or 0s Multicast addresses Class E addresses 11110bbb.bbbbbbbb.bbbbbbbb.bbbbbbbb b can be 1s or 0s Only for experimental purposes IP Addressing and Related Topics 15

16 Network, Broadcast, Multicast, and Other Special IP Addresses Network address Any IP address where all host bits are 0 Broadcast address Address that all hosts on a network must read Broadcast traffic Seldom forwarded from one physical network to another IP Addressing and Related Topics 16

17 Broadcast Packet Structures IP broadcast packets have two destination address fields Data Link layer destination address field Destination network address field IP Addressing and Related Topics 17

19 Multicast Packet and Address IP gateway Structures Router or other device that will forward traffic to the host s physical network The Internet Corporation for Assigned Names and Numbers (ICANN) Allocates multicast addresses on a controlled basis IP Addressing and Related Topics 19

22 The Vanishing IP Address Space Address space saving techniques Classless Inter-Domain Routing (CIDR) Trade in existing IP network addresses RFC 1918 Reserves three ranges of IP addresses for private use Network Address Translation (NAT) Lets networks use private IP addresses internally and maps them to public IP address externally IP Addressing and Related Topics 22

23 Understanding Basic Binary Arithmetic Four binary calculations must be mastered Converting binary to decimal Converting decimal to binary Understanding how setting increasing numbers of high-order bits to 1 in eight-bit binary numbers corresponds to specific decimal numbers Understanding how setting increasing low-order bits to 1 in eight-bit binary numbers corresponds to specific decimal numbers IP Addressing and Related Topics 23

24 Converting Decimal to Binary Converting decimal number 125 to binary 125 divided by 2 equals 62, remainder 1 62 divided by 2 equals 31, remainder 0 31 divided by 2 equals 15, remainder 1 15 divided by 2 equals 7, remainder 1 7 divided by 2 equals 3, remainder 1 3 divided by 2 equals 1, remainder 1 1 divided by 2 equals 0, remainder 1 IP Addressing and Related Topics 24

25 Converting Binary to Decimal Count the total number of digits in the number Subtract 1 from the total (8-1 = 7) Convert to exponential notation, using all the digits as multipliers converts as follows = 1*27+1*26+0*25+1*24+1*23+0*22+1*21+1*20 = = 219 IP Addressing and Related Topics 25

26 High-Order Bit Patterns Binary Decimal IP Addressing and Related Topics 26

27 Low-Order Bit Patterns Binary Decimal Exponent IP Addressing and Related Topics 27

28 IP Networks, Subnets, And Masks Subnet mask Special bit pattern that blocks off the network portion of an IP address with an all-ones pattern Default masks for Classes A, B, and C Class Layout Default Mask Class A n h.h.h Class B n.n h.h Class C n.n.n h IP Addressing and Related Topics 28

29 IP Subnets and Supernets Subnetting Stealing (borrowing) bits from the host portion to further subdivide the network portion of an address Supernetting Stealing bits from network portion Using them to create a single, larger contiguous address space for host addresses IP Addressing and Related Topics 29

30 Calculating Subnet Masks Types of subnet masking techniques Constant-length subnet masking (CLSM) Variable-length subnet masking (VLSM) In a VLSM addressing scheme Different subnets may have different extended network prefixes IP Addressing and Related Topics 30

31 Designing a Constant-Length Subnet Mask Decide how many subnets are needed Add 2 to number of subnets needed then jump to the nearest higher power of two Reserve bits of host portion s address from the top down Be sure that there are enough host addresses left over on each subnet to be usable If using RIP Use the formula 2 b 2 to calculate the number of usable subnets from a mask IP Addressing and Related Topics 31

32 Designing a Variable-Length Subnet Mask Analyze requirements for individual subnets Aggregate requirements by their relationships to the nearest power of two Use subnets that require largest number of devices To decide the minimum size of the subnet mask Aggregate subnets that require fewer of hosts Define VLSM scheme that Provides the necessary number of subnets of each size to fit its intended use best IP Addressing and Related Topics 32

33 Calculating Supernets Supernets Steal bits from network portion of an IP address to lend those bits to the host Permit multiple IP network addresses to be combined Allow an entire group of hosts to be reached through a single router address IP Addressing and Related Topics 33

34 Classless Inter-Domain Routing Limitations Network addresses must be contiguous When address aggregation occurs CIDR address blocks work best when they come in sets that are greater than 1 and equal to some lowerorder bit pattern that corresponds to all 1s Addresses commonly applied to Class C addresses To use a CIDR address on any network Routers in routing domain must understand CIDR notation IP Addressing and Related Topics 34

35 Public Versus Private IP Addresses Private IP addresses ranges May be in the form of IP network addresses Address masquerading May be performed by boundary devices that include proxy server capabilities Private IP address limitation Some IP services require a secure end-to-end connection IP Addressing and Related Topics 35

37 Public Versus Private IP Addresses Public IP addresses (continued) Remain important for identifying all servers or services that must be accessible to the Internet Most organizations need public IP addresses only for two classes of equipment Devices that permit organizations to attach networks to the Internet Servers designed to be accessible to the Internet IP Addressing and Related Topics 37

38 Managing Access To IP Address Reverse proxying Information Permits the proxy server to front for servers inside the boundary Important service that proxy server provides Manages what source addresses appear in outbound packets that pass through it IP Addressing and Related Topics 38

39 Obtaining Public IP Addresses Public IP addresses Issued by ISPs IP renumbering Switching addresses on every machine that uses address from old ISP to unique address obtained from new ISP ICANN Manages all IP-related addresses, protocol numbers, and well-known port addresses Assigns MAC layer addresses for use in network interfaces IP Addressing and Related Topics 39

40 IP Addressing Schemes IP addressing scheme constraints Number of physical locations Number of network devices at each location Amount of broadcast traffic at each location Availability of IP addresses Delay caused by routing from one network to another IP Addressing and Related Topics 40

41 The Network Space Application Specific Integrated Circuits (ASICs) Hardware used by switches to make decisions Layer-3 switch Implements the layer-3 logic from the software into its own ASICs Allows you to partition a large network into many smaller subnets with almost no loss of performance IP Addressing and Related Topics 41

42 The Host Space Reasons for using binary boundaries You may want to implement layer-3 switching to reduce the broadcast traffic One day you will want to classify your traffic to apply Quality of Service (QoS) or policies of some sort Can be applied to firewall rules IP Addressing and Related Topics 42

43 Summary IP addresses Provide foundation for identifying individual network interfaces on TCP/IP networks IP addresses Come in five classes named through E Understanding binary arithmetic Essential to knowing how to deal with IP addresses IP Addressing and Related Topics 43

44 Summary (continued) Classless Inter-Domain Routing (CIDR) Permits network-host boundary to fall away from octet boundaries Subnetting Permits additional bits to be taken from the host portion of a network Address masquerading and address substitution Techniques used to hide internal network IP addresses from outside view IP Addressing and Related Topics 44

45 Summary (continued) Within the Class A, B, and C IP address ranges IETF has reserved private IP addresses or address ranges Internet Corporation For Assigned Names and Numbers (ICANN) Ultimate authority for obtaining public IP addresses IP Addressing and Related Topics 45