GeorgeAlmeida.com Learn IP Subnetting in 15 minutes

1 Learn IP Subnetting in 15 minutes George Almeida 3-8-2015 GeoGeoGeoGeo ssssblogogogog 1 Contents Preface .. 2 Terms and Definitions .. 3 Introduction .. 3 Obtaining an IP Address for the internet .. 4 Verifying TCP/IP with IPCONFIG and PING .. 4 Microsoft TCP/IP protocol 4 IP Addressing .. 5 Address Classes .. 5 Addressing Guidelines .. 6 Private 10 Network .. 6 Converting IP addresses from Binary to 7 Subnetting .. 7 What is a segment? .. 8 Subnet Masks .. 8 Default Subnet Masks .. 9 Implementing Subnetting .. 9 Defining a Subnet Mask(one Octet) .. 10 Example - Subnetting one Octet: .. 10 Subnetting More than One Octet .. 12 Example - Subnetting more than one Octet: .. 12 Finding a Network ID given the IP address of a host and the subnet .. 14 GeoGeoGeoGeo ssssblogogogog 2 Preface I wrote this tutorial as part of a training session I conducted for co-workers back in 1999.

2 Back then, TCP/IP was relatively new to many in the IT field, especially those of us who were just started to migrate to an Ethernet network. I knew that I needed to understand the basic concepts of TCP/IP if I was to progress in my career. Therefore I took some courses and read a lot of material between 1998 -1999 and put together this brief tutorial. I have distributed this book to several IT folks over the years. Many of them who were struggling to fully understand the concept of calculating the IP subnet for various scenarios. For example, would you like to know how to manually calculate the IP scheme for a company r example uses a private class A subnet and needs 1,000 networks with an average of 750 hosts per subnet. I know that today there are IP calculators that do all of this work for you so why should you have to read or even understand the concepts of IP concepts, specifically Subnetting ?

3 I feel if you understand how IP works and how to calculate hosts and subnets manually, without a calculator, then it will help you get a better grasp of the topic. This is especially true for those who are studying to take certification exams which require mastering the understanding of calculating IP addressing without use of a calculator or other reference. If you want to fully grasp and understand the calculations behind figuring out IP subnet configurations in real world environments then please continue reading. After reading the next 14 pages, I am confident that you will be more confident in your understanding of TCP/IP protocol specifically from a Subnetting perspective. GeoGeoGeoGeo ssssblogogogog 3 Terms and Definitions Here are some terms that will be used through out the documentation: packet is a unit of information transmitted as a whole from one device to another on a network.

4 Each packet contains a set amount of data along with a header, containing information about the type of packet and the network address to which it is being sent. routable - TCP/IP packets can be routed on the internet or on a company Intranet. Routing is the process of choosing a path over which to send packets. Routing occurs at a TCP/IP host when it sends IP packets and routing also occurs at an IP router. router - a router is a device that forwards the packets from one physical network to another. Routers are commonly referred to as gateways. In both cases a decision has to be made as to where the packet is to be forwarded. To make these decisions, the IP layer consults a routing table that is stored in memory on a router and chooses the best possible path to send the packets. host - an IP host can is any device with a valid IP address on a network. It can be an Ethernet adapter, router, and a physical port on a router, a jet direct card connected to a printer.

5 Segment - when we refer to a segment or a physical segment in these notes, we are referring to a physical portion, or section of a network. Our network at XCompany is segmented. We have a segment in Branch Office 1 and a segment in branch office 2. You will see examples later. Subnetting - a subnet is NOT the same as a segment. Subnetting is used to minimize network traffic and as a way of organizing IP addresses. It's a way to apply one network across multiple physical segments. subnet mask - A subnet mask is a 32-bit address used to: Block out a portion of the IP address to distinguish the network ID from the host ID. Specify whether the destination host's IP address is located on a local network or a remote network. Introduction What is TCP/IP? Transmission Control protocol / internet protocol is an industry-standard suite of communication protocols designed for wide area networks.

6 Some of the advantages of TCP/IP include: A standard routable enterprise networking protocol . All modern operating systems offer TCP/IP support. GeoGeoGeoGeo ssssblogogogog 4 A technology for connecting dissimilar systems. Many standard connectivity utilities are available to access and transfer data between dissimilar systems, including FTP and Telnet. Offers a method of gaining access to the internet . The internet made TCP/IP popular. Obtaining an IP Address for the internet When you plan to connect your network to the worldwide internet , you must obtain the network ID portion of the IP address to guarantee IP network ID uniqueness. The network ID and host id are covered in more detail in the IP Addressing section. For domain name registration and IP network number assignment, you must contact InterNIC and register. As of this writing, the only IP addresses being assigned are Class C addresses.

7 As more and more people register domain names, IP addresses are now becoming scarce under the current release of IP version 4. The initial design did not anticipate the growth of the internet and the eventual exhaustion of the IP Version 4 address space. Therefore a new version of IP is needed. This new version (version 6) is an entirely new packet structure, which currently is incompatible with IPv4 systems. IPv6 has 129-bit source and destination IP addresses (4 times larger than IPv4). Verifying TCP/IP with IPCONFIG and PING ipconfig - does the same thing as winipcfg but is used for Windows NT. ping - after the connection is verified with the winipcfg or ipconfig utility, you can use the PING utility to test connectivity. The PING utility is a diagnostic tool that tests TCP/IP configurations and diagnoses connection problems. The command syntax is: ping IP_address Microsoft TCP/IP protocol Suite Other topics of interest concerning the architecture of TCP/IP for Microsoft are: The Microsoft TCP/IP protocol Suite - a four-layer model Transport Layer - TCP versus UDP (User Datagram protocol ) UDP does not guarantee that packets will be delivered.

8 Application Layer - Windows Sockets and NetBIOS. Windows Sockets service provides a standard application programming interface (API) to many transport protocols such as TCP/IP and IPX. NetBIOS provides a standard GeoGeoGeoGeo ssssblogogogog 5interface to protocols that support the NetBIOS naming and messaging services, such as TCP/IP and NetBEUI. internet Layer - ICMP and IGMP management protocols. ARP (address resolution protocol ) converts IP addresses to mac addresses. Network Layer - LAN technologies such as Ethernet, Token Ring and FDDI. WAN technologies such as Serial Lines, Frame Relay, T1 and others. IP Addressing What is an IP address? Each TCP/IP address is identified by a logical IP address. A unique IP address is required for each host and network component that communicates using TCP/IP. Each IP address consists of the network ID and host ID. The network ID identifies the systems that are located on the same physical segment.

9 All systems on the same physical segment must have the same network ID. The network ID must be unique to the internetwork. The host ID identifies a workstation, server, router or other TCP/IP host within a segment. The address for each host must be unique to the network ID. < -------- 32 Bits -------- > Network ID | | | | | | | | | | | | | | | | Host ID | | | | | | | | | | | | | | | | Example: Each IP address is 32 bits long and is composed of four 8-bit fields, called octets. Octets are separated by periods. The octet represents a decimal number in the range of 0 - 255. This format is called dotted decimal notation. If not for this format, you would have remember the binary equivalent of : 00001010 00000001 00001010 00000001. I'm not sure about you, but I feel it's much easier to remember Address Classes The internet has defined five IP address classes to accommodate networks of varying sizes.

10 We will Learn about the three most widely used classes, A, B and C. The class of each address defines three things: 1. which bits are used for the network ID 2. which bits are used for the host ID 3. the possible number of networks and the number of hosts per network. The following chart shows the three different classes and the information regarding the number of networks and hosts allowed for each class: GeoGeoGeoGeo ssssblogogogog 6 Number of Networks Number of Hosts per Network Range of Network IDs (1st Octet) Class A 126 16,777,214 1 - 126 Class B 16,384 65,534 128 - 191 Class C 2,097,152 254 192 - 223 Addressing Guidelines The following guidelines must be followed when assigning network Ids and host Ids: The network ID cannot be 127. This ID is reserved for loopback functions. The network ID and host ID bits cannot all be 1's. If all bits are set to 1, the address is interpreted as a broadcast rather than a host ID.