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

2. 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

3. IP Addressing and Related Topics3 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

4. IP Addressing and Related Topics4 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 172.16.1.10 –Physical numeric Six-byte numeric address, burned into firmware (on a chip) by network interface manufacturers

5. IP Addressing and Related Topics5 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

6. IP Addressing and Related Topics6 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

7. IP Addressing and Related Topics7 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

8. IP Addressing and Related Topics8 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

9. IP Addressing and Related Topics9 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 (00001010) Reserved for loopback testing –Address 127.n.n.n

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11. IP Addressing and Related Topics11 More About Class B Addresses Class B addresses take the following binary form –10bbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb –b can be 1s or 0s 2 14 – 2 –Maximum number of usable network addresses 16,366 –Maximum number of public IP addresses

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13. IP Addressing and Related Topics13 More About Class C Addresses Class C addresses take the following binary form –110bbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb –b can be 1s or 0s 2 21 – 2 –The maximum number of usable network addresses Reserved for private use –256 Class C addresses, from 192.168.0.0 to 192.168.255.255

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15. IP Addressing and Related Topics15 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

16. IP Addressing and Related Topics16 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

17. IP Addressing and Related Topics17 Broadcast Packet Structures IP broadcast packets have two destination address fields –Data Link layer destination address field –Destination network address field

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19. IP Addressing and Related Topics19 Multicast Packet and Address Structures IP gateway –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

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22. IP Addressing and Related Topics22 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

23. IP Addressing and Related Topics23 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

24. IP Addressing and Related Topics24 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

25. IP Addressing and Related Topics25 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 11011011converts as follows –11011011 = 1*27+1*26+0*25+1*24+1*23+0*22+1*21+1*20 = 128+64+0+16+8+0+2+1 = 219

26. IP Addressing and Related Topics26 High-Order Bit Patterns Binary Decimal 10000000 128 11000000 192 11100000 224 11110000 240 11111000 248 11111100 252 11111110 254 11111111 255

27. IP Addressing and Related Topics27 Low-Order Bit Patterns Binary Decimal Exponent 00000001 1 2 1 - 1 00000011 3 2 2 - 1 00000111 7 2 3 - 1 00001111 15 2 4 - 1 00011111 31 2 5 - 1 00111111 63 2 6 - 1 01111111 127 2 7 - 1 11111111 255 2 8 - 1

28. IP Addressing and Related Topics28 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 255.0.0.0 Class B n.n h.h 255.255.0.0 Class C n.n.n h 255.255.255.0

29. IP Addressing and Related Topics29 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

30. IP Addressing and Related Topics30 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

31. IP Addressing and Related Topics31 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

32. IP Addressing and Related Topics32 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

33. IP Addressing and Related Topics33 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

34. IP Addressing and Related Topics34 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 lower- order 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

35. IP Addressing and Related Topics35 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

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37. IP Addressing and Related Topics37 Public Versus Private IP Addresses (continued) Public IP addresses –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

38. IP Addressing and Related Topics38 Managing Access To IP Address Information Reverse proxying –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

39. IP Addressing and Related Topics39 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

40. IP Addressing and Related Topics40 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

41. IP Addressing and Related Topics41 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

42. IP Addressing and Related Topics42 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

43. IP Addressing and Related Topics43 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

44. IP Addressing and Related Topics44 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

45. IP Addressing and Related Topics45 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