Expl net fund_chapter_06_i_pv4_part_2

Chapter 6 Addressing the Network - IPV4 Part II

Addressing the Network: IPv4 Legacy IPv4 Addressing

Legacy IPv4 Addressing In the early 1980’s, unicast address ranges were grouped into specific sizes or classes of address. Each class defined: A specifically sized network. Specific address blocks for these networks. Class High Order Bits First Octet Range Number of Network Bits Number of Host Bits Number of Networks Number of Hosts per Network A 0 0-127 8 24 128 16,777,216 B 10 128-191 16 16 16,384 65,536 C 110 192-223 24 8 2,097,152 256 D 1110 224-239 Used for Multicasting to multiple hosts. E 1111 240-255 Reserved for research and development.

IPv4 Classful Addressing Devices examined the first octet of the address and could determine the address range. The high order bits never change for each class. Classful Addressing: 192 .168.23.2 is in the Class C range Therefore – 24 network bits and 8 hosts bits. Class High Order Bits First Octet Range Number of Network Bits Number of Host Bits Number of Networks Number of Hosts per Network A 0 0-127 8 24 128 16,777,216 B 10 128-191 16 16 16,384 65,536 C 110 192-223 24 8 2,097,152 256

IPv4 Classful Addressing In a classful addressing scheme, these divisions take place at the octet boundaries . This may seem obvious now but is important to remember when we explore how to divide a single network into several smaller subnets (subnetting) . Class High Order Bits First Octet Range Number of Network Bits Number of Host Bits Number of Networks Number of Hosts per Network A 0 0-127 8 24 128 16,777,216 B 10 128-191 16 16 16,384 65,536 C 110 192-223 24 8 2,097,152 256

IPv4 Classful Addressing In the early 1990s, the subnet mask was added to IPv4. The subnet mask allowed networks to subdivided or subnetted . Each class was assigned a default subnet mask. Class First Octet Range Number of Network Bits Number of Host Bits Default Subnet Mask Number of Networks Number of Hosts per Network A 0-127 8 24 255.0.0.0 128 16,777,216 B 128-191 16 16 255.255.0.0 16,384 65,536 C 192-223 24 8 255.255.255.0 2,097,152 256

IPv4 Classful Addressing Let’s quickly review…. In order to function properly with network devices, every IP network must contain three types of addresses: Network Address: All HOST BITS are set to 0 . Host Address: HOST BITS will vary. Broadcast Address: All HOST BITS are set to 1 . For a host to communicate directly with another host on the same network, they must have the same network portion.

IPv4 Classful Addressing SO: For every IP address range that we assign to a network segment, we automatically lose two addresses …. One for the network address (sometimes called the wire address or subnetwork address) One for the broadcast address for that network.

IPv4 Classful Addressing Our numbers for the number of hosts per network have to change to allow for the special use of the network number and broadcast addresses. As we will see, the formula (2 number_of_bits - 2 or 2 n - 2) is an important part of assigning an IP address range to a network segment. Class Number of Network Bits Number of Host Bits Number Hosts Per Network Number of Useable Hosts per Network A 8 24 2 24 = 16,777,216 2 24 - 2 = 16,777,214 B 16 16 2 16 = 65,536 2 16 - 2 = 65,534 C 24 8 2 8 = 256 2 8 - 2 = 254

IPv4 Classless Addressing The system currently in use is classless addressing . Address blocks appropriate to the number of hosts are assigned to companies or organizations without regard to the class . This is accomplished by subnetting with Variable Length Subnet Masking (VLSM) . To understand classless addressing, you must first understand classful addressing.

Addressing the Network: IPv4 Calculating Addresses

Calculating Addresses Skills: To work with an IPv4 network: Find the network address for the host. Find the broadcast address for the network. Find what host addresses are available in the network. Divide a large network into smaller networks.

The Network Number A host on a network can communicate directly with other devices on the same network, only if all the devices have the same network number and the same subnet mask .

The Network Number Routers use the network number to build their routing tables so it cannot be used for a host . The IP address that indicates the network number has all 0 bits in the host portion of the IP Address.

The Broadcast If a host needs to send a broadcast , it also uses the network number with all of the host bits set to 1 . A broadcast address is used for that purpose only and cannot be assigned to a host .

The Host Number The host number is the portion of the IP address that uniquely identifies the individual host on that network.

The Subnet Mask Subnet Mask: Let's not forget about the subnet mask. Each class has a default or "natural" subnet mask based on the default number of bits used for the network and host portion. Class Number of Network Bits Number of Host Bits Default Prefix Default Subnet Mask A 8 24 /8 255.0.0.0 B 16 16 /16 255.255.0.0 C 24 8 /24 255.255.255.0

Classful IP Addressing – Class C Class C: Address range: 192 - 223 Number of network bits: 24 Number of networks: 2,097,152 Number of host bits: 8 Number of hosts per network: 2 8 = 256 Number of Useable Hosts per network: 2 8 - 2 = 254 Default Subnet Mask: 255.255.255.0 or /24

Classful IP Addressing – Class C We know from the Class C subnet mask (255.255.255.0) : The first 24 bits are the network number and the last 8 bits are the host numbers. 11111111 01001101 00010100 11010010 255 77. 20. 210. The last host address (all 1's) is reserved for the broadcast address. 00000000 01001101 00010100 11010010 0 77. 20. 210. The first host address (all 0's) is reserved for the network address.

Classful IP Addressing – Class C Because the host portion of the subnet mask is all zero's (255.255.255. 0 ), the remaining host addresses can be used for individual hosts on the network. The number of usable host addresses for the entire network is 2 8 - 2 = 254 11111110 01001101 00010100 11010010 254 77. 20. 210. 00000001 01001101 00010100 11010010 1 77. 20. 210. The range of available addresses is:

Classful IP Addressing – Class B Class B: Address range: 128 - 191 Number of network bits: 16 Number of networks: 16,384 Number of host bits: 16 Number of hosts per network: 2 16 = 65,536 Number of Useable Hosts per network: 2 16 - 2 = 65,534 Default Subnet Mask: 255.255.0.0 or /16

Classful IP Addressing – Class B We know from the Class B subnet mask (255.255.0.0) : The first 16 bits are the network number and the last 16 bits are the host numbers. 11111111 11111111 01010100 10010010 255 255. 84. 146. The last host address (all 1's) is reserved for the broadcast address. 00000000 00000000 01010100 10010010 0 0. 84. 146. The first host address (all 0's) is reserved for the network address.

Classful IP Addressing – Class B Because the host portion of the subnet mask is all zero's (255.255. 0.0 ), the remaining host addresses can be used for individual hosts on the network. The number of usable host addresses for the entire network is 2 16 - 2 = 65,534 11111110 11111111 01010100 10010010 254 255. 84. 146. 00000001 00000000 01010100 10010010 1 0. 84. 146. The range of available addresses is:

Classful IP Addressing – Class A Class A: Address range: 0 - 127 Number of network bits: 8 Number of networks: 126 Number of host bits: 24 Number of hosts per network: 2 24 = 16,777,216 Number of Useable Hosts per network: 2 24 - 2 = 16,777,214 Default Subnet Mask: 255.0.0.0 or /8

Classful IP Addressing – Class A Class A (Usable Networks): An address range of 0 –127 is 128 networks. The actual number of usable networks for Class A is 126. Network 0 is reserved for special use for default routes. Network 127 is reserved as a loopback network. The address 127.0.0.1 is automatically available in every device after TCP/IP has been installed. If you "ping" that address and get a good response, it means that TCP/IP is installed correctly.

Classful IP Addressing – Class A We know from the Class A subnet mask (255.0.0.0) : The first 8 bits are the network number and the last 24 bits are the host numbers. 11111111 11111111 11111111 01000010 255 255. 255. 66. The last host address (all 1's) is reserved for the broadcast address. 00000000 00000000 00000000 01000010 0 0. 0. 66. The first host address (all 0's) is reserved for the network address.

Classful IP Addressing IP Address: 130.61.22.204 / 16 Network Address is: Broadcast Address is: Subnet Mask: Number of Useable host addresses: What are they? Address Class: B 130.61.0.0 255.255.0.0 130.61.255.255 2 16 - 2 = 65,534 130.61.0.1 - 130.61.255.254

Classful IP Addressing IP Address: 197.101.28.83 / 24 Network Address is: Broadcast Address is: Subnet Mask: Number of Useable host addresses: What are they? Address Class: C 197.101.28.0 255.255.255.0 197.101.28.255 2 8 - 2 = 254 197.101.28.1 - 197.101.28.254

Classful IP Addressing IP Address: 64.133.65.101 / 8 Network Address is: Broadcast Address is: Subnet Mask: Number of Useable host addresses: What are they? Address Class: A 64.0.0.0 255.0.0.0 64.255.255.255 2 24 - 2 = A Bunch! 64.0.0.1 - 64.255.255.254

Addressing the Network: IPv4 Basic Subnetting

IP Address Crisis The world is running short of available IP addresses. If every organization connected to the Internet used an entire Class A, B or C address: The number of organizations would be limited and many IP addresses would be wasted. e.g. An organization with 256 hosts owns a Class B address. 65,000 addresses not used. Owning an address means that the organization has applied for and received that address range from the IANA.

IP Address Crisis The goal, then, is to use owned addresses (or public addresses) as efficiently as possible to avoid waste. Subnetting CIDR Network Address Translation (NAT). It is also desirable to avoid waste within the organization when using private IP addressing. Careful planning of the addressing scheme is key to a successful implementation.

Why Multiple Segments? If organizations grow significantly, the physical segment and the logical network traffic can quickly become unmanageable. Solution? Break the larger network into smaller, more manageable segments. Router: Each segment becomes physically smaller and each must have their own unique, logical, Layer 3 network address.

Why Multiple Segments? This company has multiple networks connected by a router. The network number for each network must be unique . The company IT headquarters has assigned a Class B address of 131.15.0.0 to use for ALL these networks.

Why Multiple Segments? Class B 131.15.0.0 What happens here? 131.15.1.0 131.15.2.0 131.15.3.0 131.15.4.0 131.15.5.0 Subnetting

Why Multiple Segments? Network numbers MUST be unique. You should: Plan what you need. Plan for the future. Make efficient use of addresses. 131.15.1.0 131.15.3.0 131.15.4.0 131.15.5.0 131.15.2.0 131.15.6.0 131.15.7.0 Subnetting

Creating a Subnet To subnet a network, the IP address host portion of the subnet mask is divided into two parts. Bits are borrowed from the host portion and assigned to the network portion to create a new network address. The new network address covers a smaller portion of the original network number. It is a sub-network of the original or a subnet .

Creating a Subnet The borrowed bits become part of the network portion of the IP Address and form the network number . The remaining host bits become the host portion and are used to identify individual network hosts and create broadcasts for the new subnet.

Creating a Subnet The subnet mask changes to reflect the new network/host bit assignment. The same subnet mask applies to ALL networks derived from the subnetting process. Original Subnet Mask: 255.255.0.0 11111111.11111111.00000000.00000000 Borrow 8 bits: 11111111.11111111. 11111111 .00000000 New Subnet Mask: 255.255.255.0

Creating a Subnet - The Rules Host bits must be borrowed in descending order , starting with the left-most bit position and working to the right. A minimum of two bits must remain for host addresses. A remaining host mask of all 0's or all 1's cannot be assigned as a host address. To determine the number of subnets or hosts: Subnets: 2 number_of_ borrowed_host _bits Usable Hosts Per Subnet: 2 number_of_ remaining_host _bits - 2

Subnets and Useable Hosts – Class C Default: 255.255.255.0 - 24 network bits and 8 host bits Leave at least 2 Borrowed Bits Number of Subnets Number of Usable Hosts Subnet Mask Prefix 0 0 (default) 2 8 - 2 = 254 255.255.255.0 /24 1 2 1 = 2 2 7 - 2 = 126 255.255.255.128 /25 2 2 2 = 4 2 6 - 2 = 62 255.255.255.192 /26 3 2 3 = 8 2 5 - 2 = 30 255.255.255.224 /27 4 2 4 = 16 2 4 - 2 = 14 255.255.255.240 /28 5 2 5 = 32 2 3 - 2 = 6 255.255.255.248 /29 6 2 6 = 64 2 2 - 2 = 2 255.255.255.252 /30 7 2 7 = 128 2 1 - 2 = 0 unusable

Subnetting - Class C This is our network and we have decided to use the private Class C network: 192.168.80.0 We need 4 networks with addresses for 5 hosts and want to leave room for some future expansion . Borrowed Bits Number of Subnets Number of Usable Hosts Subnet Mask Prefix 2 2 2 = 4 2 6 - 2 = 62 255.255.255.192 /26 3 2 3 = 8 2 5 - 2 = 30 255.255.255.224 /27 4 2 4 = 16 2 4 - 2 = 14 255.255.255.240 /28 5 2 5 = 32 2 3 - 2 = 6 255.255.255.248 /29

Subnetting - Class C Looking at the table, we see that borrowing 3 bits gives us 8 subnets with 30 useable hosts on each network. This choice meets the current requirements and leaves room for expansion. Borrowed Bits Number of Subnets Number of Usable Hosts Subnet Mask Prefix 2 2 2 = 4 2 6 - 2 = 62 255.255.255.192 /26 3 2 3 = 8 2 5 - 2 = 30 255.255.255.224 /27 4 2 4 = 16 2 4 - 2 = 14 255.255.255.240 /28 5 2 5 = 32 2 3 - 2 = 6 255.255.255.248 /29

Magic Numbers To make the job of subnetting easier, there is a method that allows you to calculate a "magic" number. The magic number we're looking for is the number of addresses in each network, including the network, broadcast and host range . The calculation 2 number_ of_ host_ bits yields the "magic" number. We have 5 host bits remaining so….. 2 5 = 32 - our "magic" number.

Subnetting - Class C Network: 192.168.80.0 Subnet Mask: 255.255.255.224 Network: 27 bits Host: 5 bits Magic Number: 2 5 = 32 192.168.80.255 192.168.80.225 – 192.168.80.254 192.168.80.224 7 192.168.80.223 192.168.80.193 – 192.168.80.222 192.168.80.192 6 192.168.80.191 192.168.80.161 – 192.168.80.190 192.168.80.160 5 192.168.80.159 192.168.80.129 – 192.168.80.158 192.168.80.128 4 192.168.80.127 192.168.80.97 – 192.168.80.126 192.168.80.96 3 192.168.80.95 192.168.80.65 – 192.168.80.94 192.168.80.64 2 192.168.80.63 192.168.80.33 – 192.168.80.62 192.168.80.32 1 192.168.80.31 192.168.80.1 – 192.168.80.30 192.168.80.0 0 Broadcast Address Subnet Address Range Network Address ID

Subnetting – Class C Result is 8 subnets with 30 useable hosts each. Allows the expansion of hosts in each network and the addition of two more networks without changing our IP Addressing scheme . 192.168.80.0/27 192.168.80.32/27 192.168.80.64/27 192.168.80.96/27

Subnetting – Class A or Class B The subnetting process for class A and B networks is the same. You are simply working with more bits. Determine what is required. Number of networks and number of hosts per network. Determine the number of bits to be borrowed. Determine your magic number. Subnet to produce the ranges for each subnetwork.

Subnetting - Class B Let's try one. You are the network administrator for a world-wide organization with 7,500 users. (Yep – the head IT honcho!) You have 10 world-wide central offices and each of those have their own networks and branch offices. Central and Branch office networks range from 100 to 3,000 users . You have decided that a Class B network will be sufficient for your needs and you must subnet the network to include yourself and the central offices. Each central office handles their own network maintenance and it will be up to them to further subnet the network you design.

Subnetting - Class B You have decided to use the Class B private address of 172.25.0.0 / 16 Head Office Central 01 Central 02 Central 03 Central 10 Branch 01 Branch nn Your objective is to provide enough addresses so that each central office can cover their branches and allow room for future expansion.

Subnetting - Class B Head Office + 10 Central Offices ---100 to 3,000 users each Borrowed Bits Number of Subnets Number of Usable Hosts Subnet Mask Prefix 0 0 (default) 2 16 - 2 = 65,534 255.255.0.0 /16 1 2 1 = 2 2 15 - 2 = 32,766 255.255.128.0 /17 2 2 2 = 4 2 14 - 2 = 16,382 255.255.192.0 /18 3 2 3 = 8 2 13 - 2 = 8,190 255.255.224.0 /19 4 2 4 = 16 2 12 - 2 = 4,094 255.255.240.0 /20 5 2 5 = 32 2 11 - 2 = 2,046 255.255.248.0 /21 6 2 6 = 64 2 10 - 2 = 1,022 255.255.252.0 /22 7 2 7 = 128 2 9 - 2 = 510 255.255.254.0 /23 8 2 8 = 256 2 8 - 2 = 254 255.255.255.0 /24

Subnetting – Class B Determining your magic number – Class A and B. The trick here in determining the magic number is to only work with the remaining host bits up to a total of 8 . The rest of the bits will fall in line as host bits. e.g. Borrow 4 bits – subnet mask 255.255.240.0 11111111.11111111. 1111 0000.00000000 4 remaining host bits: 11111111.11111111.1111 0000 .00000000 Magic Number = 2 4 = 16

Subnetting – Class B 172.25.255.255 15 14 13 12 11 10 9 8 7 6 5 4 172.25.63.255 172.25.48.1 to 172.25.63.254 172.25.48.0 3 172.25.47.255 172.25.32.1 to 172.25.47.254 172.25.32.0 2 172.25.31.255 172.25.16.1 to 172.25.31.254 172.25.16.0 1 172.25.15.255 172.25.0.1 to 172.25.15.254 172.25.0.0 0 Broadcast Address Subnet Address Range Network Address ID 172.25.239.255 172.25.223.255 172.25.207.255 172.25.191.255 172.25.175.255 172.25.159.255 172.25.143.255 172.25.127.255 172.25.111.255 172.25.95.255 172.25.79.255 172.25.240.1 to 172.25.255.254 172.25.224.1 to 172.25.239.254 172.25.208.1 to 172.25.223.254 172.25.192.1 to 172.25.207.254 172.25.176.1 to 172.25.191.254 172.25.160.1 to 172.25.175.254 172.25.144.1 to 172.25.159.254 172.25.128.1 to 172.25.143.254 172.25.112.1 to 172.25.127.254 172.25.96.1 to 172.25.111.254 172.25.80.1 to 172.25.95.254 172.25.64.1 to 172.25.79.254 172.25.240.0 172.25.224.0 172.25.208.0 172.25.192.0 172.25.176.0 172.25.160.0 172.25.144.0 172.25.128.0 172.25.112.0 172.25.96.0 172.25.80.0 172.25.64.0

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