IP Addressing  To go somewhere on the Internet, you must type a Uniform Resource Locator (URL).  A query is sent to the nearest DNS (Domain Name System) server to translate the URL to an IP address.  Routers and switches that run the Internet don’t recognize domain names.  All internet addresses are IP addresses.  IANA (Internet Assigned Number Authority) issues IP addresses.  InterNIC (Internet’s Network Information Center) it is the organization that issues domain names.

IP Addressing  These two organization make sure that IP addresses and domain names are unique.  Every node on the Internet must have an IP address.  IP addresses are 32 bits long and divided into four sections, each 8bits long, called octets.  From bits to dotted-decimal format  Invented so people called read binary IP addresses  Dotted decimal takes its name from the fact that it converts bits to decimal numbers for each octet, punctuated with periods.

IP Addressing  Two reserved addresses  Broadcast octet – 255  Network Octet – 0  IP address classes  IETF (Internet Engineering Task Force) divided IP addresses into three general classes (plus two specialized ones).  This designation of ranges is called the first octet rule.  The majority of networks are numbered using either Class B or Class C IP addresses. The first octet ranges for each class are as follows:

IP Addressing  0 to 127 Class A  range of network numbers is to for 128 networks.  However, the network must not consist of only 0's, and is reserved for loopback. What's left are 126 networks-1 to 126  There are 16,777,214 possible host addresses (16,777,216 minus 2).  128 to 191 Class B  range of network numbers is to for 16,384 networks.  There are 65,534 possible host addresses (65,536 minus 2).

IP Addressing  192 to 223 Class C  range of network numbers is to for 2,097,152 networks.  There are 254 possible host addresses (256 minus 2).  224 to 254  Are reserved for two special classes (multicasting and research)  Private Addressing  The IANA reserved three blocks of IP addresses for private addresses.  A private IP address is one that is not registered with the IANA and will not be used beyond the bounds of the enterprise's internetwork-in other words, not on the Internet.  Privately numbered internetworks are also sometimes called private internets.

IP Addressing  to  The 10 block is a single Class A network number.  to  The 172 block is 16 contiguous Class B network numbers.  to  The 192 block is 256 contiguous Class C network numbers.  Two IP address translation services are used to assign valid public Internet IP numbers temporarily to hosts with permanent private IP addresses.  One technique is Network Address Translation (NAT), and the other is Port Address Translation (PAT).

IP Addressing  NAT – assigns unique reusable public IPs  PAT – assigns global address  Advantage of Private Addressing  virtually unlimited address space for numbering internal networks and hosts.  hackers see no indication of the private internetwork's topology.

Subnetting  Subnetting is the practice of squeezing more network addresses out of a given IP address than are available by default.  IP address classes define which bits, by default, will address networks versus hosts. What by default means here is that upon reading the first octet in an address, a router knows which bits to treat as network address bits.  However, in the real world, most enterprises need more network address space than they are assigned by their ISPs. This creates the need to "cheat" by claiming some of the default host bits for use in addressing networks. This is done by reassigning bits from the host portion of the IP address to the network portion.

Subnetting  Whole Octet Subnet Example  Class B public IP address –  Subnetted the entire third octet  254 subnetworks  254 hosts per subnetwork  What Subnet Masks Look Like and Where They Exist  All subnet masks are 32 bits in length.  masks are not addresses  they are overlays that define how an IP address is to be used

Subnetting  They differ from IP addresses in two key ways:  Form A subnet mask is represented as a string of 1's in binary, or a number-like 255-in dotted-decimal format.  Location A subnet mask is applied to a specific host network interface and within the configuration file of the router to which the subnetwork is attached.  Ex. The interface's proper IP address is (a Class B address), and the subsequent tells the router to subnet the entire third octet

Subnetting  Partial Octet Subnetting  In most cases, however, subnets aren't quite so simple. This is because most enterprises are issued Class C IP addresses, where only the fourth octet is reserved, by default, as host address space. In these cases, the subnet mask extends only partway into the host address space, and is thus represented by a dotted-decimal number less than 255.  Ex  This is one of two so-called.240 masks-this one permitting up to 14 subnets. Each subnet in this example has enough address space for 14 hosts-for a total of 196 possible hosts.

Subnetting

 Subnetting is a mechanism for using some bits in the host ID octets as a subnet-id.  Without subnetting = network-id + host id  With subnetting = net-id + subnet-id + host-id  Subnet is a subdivision of a network  Subnetting is used when a single network ID is subdivided into multiple network IDs by applying custom subnet mask.

Subnetting  Defining Networks by IP address  – class Ahosts – 16, 777, 214  128 – 191 – class Bhosts – 65, 534  192 – 223 – class Chosts – 254  In binary  Class A – starts at 0  Class B – starts at 10  Class C – starts at 110

Subnetting  Subdividing a network  Internetwork are networks made up of individual segments connected by routers.  The reason for having distinct segments are as follows:  To permit physically remote LAN connections.  To mix network technologies such as Ethernet and token ring, on a single logical network  To allow an unlimited number of hosts to communicate, regardless of the underlying topology.  To reduce network congestion because broadcasts and logical network traffic are limited to the logical segment  Each segment is a subnet of the internetwork and requires a unique network ID.

Five Steps of Subnetting a Network  Step 1: Determine the Number of Network IDs Required  A unique network ID is required for each of the following :  Each subnet  Each WAN connection  Step 2: Determine the number of Host IDs per Subnet Required  Ahost ID is required for each of the following:  Each TCP/IP computer network interface card  Each TCP/IP printer network interface card  Each router interface on each subnet

Five Steps of Subnetting a Network  Step 3: Define the Subnet Mask  Gives the desired number of subnets and allows enough host per subnet  Ex. Class B network ID of  Default subnet mask –  Valid host IDs – –  IP address –  Binary –  Subnet mask –  Network ID –

Five Steps of Subnetting a Network  Step 3: Define the Subnet Mask  Ex. Add 3 bits  New subnet mask   Can create different network IDs  –  –  –  –  –  –  Step 4: Define the Network IDs to Use  Step 5: Define the Host IDs to Use