Networking Fundamentals Part of the SolarWinds IT Management Educational Series VOLU me 6 IP Addressing This paper examines IP Addressing with an emphasis on understanding how address are allocated and managed. As part of the Network Fundamentals series, it is meant to be an introductory level paper. Networking Fundamentals » Volume 6, IP Addressing Page 2 Table of Contents Section 1 — IP Terminology and Number Formats ......... 3 Section 2 — IPv4 Classful IP Addressing..................4 Private IP Addresses .................................4 Network Address Translation (NAT)...................5 Section 3 — Classless Internet Domain Routing (CIDR) Addressing . 6 Requesting a Registered CIDR Block ...................6 Section 4 — Device IP Address Configuration.............8 Dynamic Host Configuration Protocol (DHCP) .........13 Section 5 — IPv6 .......................................9 Address Formats ....................................9 Special Address Types ...............................9 Other Notable IPv6 Features..........................9 Section 6 — Review ...................................10 Related SolarWinds Products ............................11 About SolarWinds......................................12 About the Author.......................................12 Copyright© 1995–2010 SolarWinds. 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IN NO EVENT SHALL SOLARWINDS, ITS SUPPLIERS OR ITS LICENSORS BE LIABLE FOR ANY DAMAGES, WHETHER ARISING IN TORT, CONTRACT OR ANY OTHER LEGAL THEORY EVEN IF SOLARWINDS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Document Revised: Oct 1, 2010 Networking Fundamentals » Volume 6, IP Addressing Page 3 SectiON 1 So to translate 172 I see that the bit in position 8 has the closest value to 172 so I set that to 1. Now I subtract 128 from 172 to get 44. The bit IP Terminology and that is closest to, but less than 44 is in position 6, so I set this to 1 and add its decimal value to 128 to get 160. Getting closer! Now 12 remains. Number Formats We can’t use the bit in position 5 as 16 is larger than 12, bus seeing as I need to represent 12 the bits in positions 3 and 4 will take care of this. Before we dive into the details of what IP addresses are, how there are So the resulting bit format translation of the decimal 172 is 10101100 or assigned and how they are routed we should make sure some of the basic (see Figure 2): concepts are covered. Figure 2. For computing purposes, one of three notations is normally used to represent numbers. These are Hexadecimal, a base 16 system, decimal, a base 10 system and binary (base 2) system. Here is a quick review of these number systems and how they are used to represent numbers in IP addressing. Decimal IP Addresses are base 10 numbers, also known as dotted (or dot) decimal format and are in the standard form of XXX.XXX.XXX.XXX, Translating the remaining octets we get the full bit format address of 10 where X is a single digit between 0 and 9 inclusive. 172.16.5.54 is an 101100.00010000.00000101.00110110. example of an IP address in dotted decimal format. This format is the most human-readable of the three. We are accustomed to representing Hexadecimal (Hex) Address Table 1. numbers base 10. Translation is easiest done from bit format rather than directly from a Nibble Decimal Hex Binary IP Addresses are binary numbers in the standard format of decimal number. Hex IPv6 address 0000 0 0 xxxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx, where x is either 1 or 0. Each numbers are four digits per octet set of eight bits are divided by dots is called a byte or octet. While each with each digit having a value of 0001 1 1 individual bit can only be a 1 or a 0, the position of each bit in the octet 0 to F, making 16 possible values 0010 2 2 gives it an order of significance. Let’s examine one octet and see how per digit. The standard format 0011 3 3 this works. (see Figure 1). of a hex IPv6 address is XXXX: XXXX:XXXX:XXXX:XXXX:XXXX: 0100 4 4 Figure 1. XXXX:XXXX. Translation of a bit 0101 5 5 format number to hex is done by 0110 6 6 breaking each bit octet into two nibbles, or half octets and then 0111 7 7 translating each nibble to a hex 1000 8 8 value. A decimal to hex value table 1001 9 9 can be useful in translating to hex Each bit in the octet occupies a position relative to the other bits. The as we are more accustomed to 1010 10 A bit on the far right in known as the least significant bit as its maximum dealing with decimal numbers. 1011 11 B value when the bit is set to 1, is a decimal 1. This bit can only represent a To the right (Table 1) is a bit to 1100 12 C decimal 0 or 1. Moving to the left, the bit in position 2 also has the possible decimal to hex table. 1101 13 D bit values of 1 or 0 and possible decimal values of 0 and 2 only. Below is a table showing each So even though each bit can only be a 1 or a 0, the position number the bit nibble in the IPv4 address 1110 14 E occupies allows it to represent a maximum decimal value of 2n, where n 172.16.5.54 and the nibbles hex 1111 15 F is the bit position. Being that the bit on the far left has the decimal value equivalents (see Table 2). of 128 it is known as the most significant bit. Table 2. Let’s take a look at the sample dotted decimal IP address of 172.16.5.54 and how it is represented in bit format. Because each section of a dotted 1010 1100 0001 0000 0000 0101 0011 0110 decimal address is derived from an octet of bits, they are also referred to A C 1 0 0 5 3 6 as octets. To translate a dotted decimal address into a bit format address, each octet is translated independently. To translate a decimal number to So in proper hex format, the dotted decimal address 172.16.5.54 is bit format follow these steps: 0xAC010536 or AC:01:05:36. Hex format is most commonly used to represent Media Access Control (MAC) addresses and IPv6 addresses 1. Locate the bit with a decimal value closest to, but less than the decimal partially due to the ability of hex to represent large numbers in a compact value to translate. format. 2. Set that bit to 1 3. Subtract the decimal value of that bit from the original decimal number. 4. Locate the bit with a decimal value closest to, but less than the decimal value calculated in step 3. 5. Set that bit to 1 6. Continue until the sum of the decimal values for all bits set to 1 equals the original decimal number. Networking Fundamentals » Volume 6, IP Addressing Page 4 SectiON 2 Below are screen captures showing class B (Figure 4) and class C (Figure 5) sample network addresses. Note the changes in how bits are shown in IPv4 Classful IP Addressing the Subnet Bit Mask sections. When IP networking first began, the standard format for any IP address Figure 4. Class B Figure 5. Class C was to specify the network number in the first octet and the remaining three octets were called the rest. Only a few governmental and educational networks that had any ability to access the Internet, then called the ARPANET (Advanced Research Projects Agency Network). ARPANET began using packet switching protocols like X.25 and switched over to TCP/IP January 1, 1983. It soon became apparent that the 254 network addresses that the original design allowed would be quickly exhausted. The classful IP addressing system provides about 3.7 billion unique IP RFC 791 was already in the works. This RFC describes in detail several addresses as shown below in Table 3. of the internet protocols and a new form of addressing that extends the flexibility of network addressing — Classful IP Addressing. Classful Table 3. addressing allows for the division of what was the rest field to allow for Number of significantly more networks. Here is how classful address is defined. Number of Address per • The most significant bits of the first octet signify the network class Class Applicable Networks Networks Network • If the most significant bit is 0, this is a class A network and the A 1.0.0.0 – 126.0.0.0 126 16,777,214+ next 7 bits represent the network number. The remaining 24 bits B 128.0.0.0 – 191.255.0.0 16,384+ 65,534 represent host addresses. C 192.0.1.0 – 223.255.255.0 2,097,151 254 • If the first 2 most significant bits are 1 0, this is a class B network and the remaining 14 bits of the first 2 octets represent the network This was assumed to allow for plenty of unique IP addresses for the number and the last 2 octets represent host addresses.