A classic TCP / IP basics of English articles INTRODUCTIONWhen you configure the TCP / IP protocol on a Microsoft Windows computer, an IP address, subnet mask, and usually a default gateway are required in the TCP / IP configuration settings.
To configure TCP / IP correctly, it is necessary to understand how TCP / IP networks are addressed and divided into networks and subnetworks. This article is intended as a general introduction to the concepts of IP networks and subnetting. A glossary is included at the end of article. MORE INFORMATIONThe success of TCP / IP as the network protocol of the Internet is largely because of its ability to connect together networks of different sizes and systems of different types. These networks are arbitrarily defined into three main classes (along with a few others) that have predefined sizes, each of which can be divided into smaller subnetworks by system administrators. A subnet mask is used to divide an IP address into two parts. One part identifies the host (computer), the other part identifies the network to WHICH IT Belongs. To Better Understand How IP Addresses and Subnet Masks Work, Look AT An IP (Internet Protocol) Address and See How IT Is Organized. IP Addresses: Networks and Hostsan IP Address IS A 32-bit Number That Unique Identifies A Host (Computer Or Other Device, SUCH AS A Printer or Router) ON A TCP / IP NetWork.
IP addresses are normally expressed in dotted-decimal format, with four numbers separated by periods, such as 192.168.123.132. To understand how subnet masks are used to distinguish between hosts, networks, and subnetworks, examine an IP address in binary notation.
For example, the dotted-decimal IP address 192.168.123.132 is (in binary notation) the 32 bit number 110000000101000111101110000100. This number may be hard to make sense of, so divide it into four parts of eight binary digits.These eight bit sections are known as octets. The example IP address, then, becomes 11000000.10101000.01111011.10000100. This number only makes a little more sense, so for most uses, convert the binary address into dotted-decimal format (192.168.123.132). The decimal numbers separated by Periods are the octets converted from binary to decimal notation.
For a TCP / IP wide area network (WAN) to work efficiently as a collection of networks, the routers that pass packets of data between networks do not know the exact location of a host for which a packet of information is destined. Routers only know what network the host is a member of and use information stored in their route table to determine how to get the packet to the destination host's network. After the packet is delivered to the destination's network, the packet is delivered to the appropriate host.
For this process to work, an IP address has two parts. The first part of an IP address is used as a network address, the last part as a host address. If you take the example 192.168.123.132 and divide it into these two parts you get the following:. 192.168.123 Network .132 Host -or- 192.168.123.0 - network address 0.0.0.132 - host address Subnet maskThe second item, which is required for TCP / IP to work, is the subnet mask... THE SUBNET MASK IS Used by The TCP / IP Protocol To Determine WHETHER A HOST IS ON The Local Subnet OR ON A Remote NetWork.
In TCP / IP, the parts of the IP address that are used as the network and host addresses are not fixed, so the network and host addresses above can not be determined unless you have more information. This information is supplied in another 32-bit number . called a subnet mask in this example, the subnet mask is 255.255.255.0 It is not obvious what this number means unless you know that 255 in binary notation equals 11111111; so, the subnet mask is:. 11111111.11111111.11111111.0000000 Lining up the IP address and the subnet mask together, the network and host portions of the address can be separated: 11000000.10101000.01111011.10000100 - IP address (192.168.123.132) 11111111.11111111.11111111.00000000 - Subnet mask (255.255.255.0) The first 24 bits (the number of ones in the subnet mask) are identified as the network address, with the last 8 bits (the number of remaining zeros in the subnet mask) identified as the host address This gives you the following:. 11000000.10101 000.01111011.00000000 - Network address (192.168.123.0) 00000000.00000000.00000000.10000100 - Host address (000.000.000.132) So now you know, for this example using a 255.255.255.0 subnet mask, that the network ID is 192.168.123.0, and the host address is 0.0.0.132. When a packet arrives on the 192.168.123.0 subnet (from the local subnet or a remote network), and it has a destination address of 192.168.123.132, your computer will receive it from the network and process IT.
Almost all decimal subnet masks convert to binary numbers that are all ones on the left and all zeros on the right Some other common subnet masks are:. Decimal Binary 255.255.255.192 1111111.11111111.1111111.11000000 255.255.255.224 1111111.11111111.1111111.11100000 Internet RFC 1878 (available from http://www.internic.net) describes the valid subnets and subnet masks that can be used on TCP / IP networks. Network classesInternet addresses are allocated by the InterNIC (http://www.internic.net), the organization that administers the Internet. These IP addresses are divided into classes. The most common of these are classes A, B, and C. classes D and E exist, but are not generally used by end users. Each of the address classes has a different default Subnet Mask. You CAN Identify The Class of An IP address by Looking at ITS First Oct. Following Area The Ranges of Class A, B, AND C Internet Addresses, Each With An Example Address:? Class A Netw orks use a default subnet mask of 255.0.0.0 and have 0-127 as their first octet. The address 10.52.36.11 is a class A address. Its first octet is 10, which is between 1 and 126, inclusive.? Class B networks Use a default subnet mask of 255.255.0.0 and have 128-191 as their first actens. The address 172.16.52.63 is a class b address. ITS First OcTet IS 172, Which Is Between 128 and 191, Inclusive.?
Class C networks use a default subnet mask of 255.255.255.0 and have 192-223 as their first octet. The address 192.168.123.132 is a class C address. Its first octet is 192, which is between 192 and 223, inclusive. In some scenarios, the default subnet mask values do not fit the needs of the organization, because of the physical topology of the network, or because the numbers of networks (or hosts) do not fit within the default subnet mask restrictions. The next section explains how networks can be divided using subnet masks. SubnettingA Class A, B, or C TCP / IP network can be further divided, or subnetted, by a system administrator. This becomes necessary as you reconcile the logical address scheme of the Internet (the abstract world of IP addresses and subnets) with the physical networks in use by the real world.A system administrator who is allocated a block of IP addresses may be administering networks that are not organized in a way that easily fits these addresses. For example, you have a wide area network with 150 hosts on three networks (in different cities) that are connected by a TCP / IP router. Each of these three networks has 50 hosts. You are allocated the class C network 192.168.123.0. (For illustration, This means 192.168.123.1 to 192.168.123.1 To 192.168.123.254 for your 150 hosts.
Two addresses that can not be used in your example are 192.168.123.0 and 192.168.123.255 because binary addresses with a host portion of all ones and all zeros are invalid. The zero address is invalid because it is used to specify a network without specifying a host . The 255 address (in binary notation, a host address of all ones) is used to broadcast a message to every host on a network. Just remember that the first and last address in any network or subnet can not be assigned to any individual host. you should now be able to give IP addresses to 254 hosts. This works fine if all 150 computers are on a single network. However, your 150 computers are on three separate physical networks. Instead of requesting more address blocks for each network, you divide Your Network Into Subnets That Enable You To Use ONE BLOCK OF Addreses on Multiple Physical Networks.
In this case, you divide your network into four subnets by using a subnet mask that makes the network address larger and the possible range of host addresses smaller. In other words, you are 'borrowing' some of the bits usually used for the host address , and using them for the network portion of the address. The subnet mask 255.255.255.192 gives you four networks of 62 hosts each. This works because in binary notation, 255.255.255.192 is the same as 1111111.11111111.1111111.11000000. The first two digits of the last octet become network addresses, so you get the additional networks 00000000 (0), 01000000 (64), 10000000 (128) and 11000000 (192). (Some administrators will only use two of the subnetworks using 255.255.255.192 as a subnet mask. for more information on this topic, see RFC 1878.) In these four networks, the last 6 binary digits can be used for host addresses.Using a subnet mask of 255.255.255.192, your 192.168.123.0 network then becomes the four networks 192.168.123.0, 192.1 . 68.123.64, 192.168.123.128 and 192.168.123.192 These four networks would have as valid host addresses: 192.168.123.1-62 192.168.123.65-126 192.168.123.129-190 192.168.123.193-254 Remember, again, that binary host addresses With all ones or all zeros Are Invalid, SO You Cannot USE Addresses with The Last OcTet Of 0, 63, 64, 127, 128, 191, 192, or 255.
You can see how this works by looking at two host addresses, 192.168.123.71 and 192.168.123.133. If you used the default Class C subnet mask of 255.255.255.0, both addresses are on the 192.168.123.0 network. However, if you use the subnet mask of 255.255.255.192, they are on different networks; 192.168.123.71 is on the 192.168.123.64 network, 192.168.123.133 is on the 192.168.123.128 network Default gatewaysIf a TCP / IP computer needs to communicate with a host on. another network, it will usually communicate through a device called a router. In TCP / IP terms, a router that is specified on a host, which links the host's subnet to other networks, is called a default gateway. This section explains how TCP / IP determines whether or not to send packets to its default gateway to reach another computer or device on the network.When a host attempts to communicate with another device using TCP / IP, it performs a comparison process using the defined subnet mask and the destination IP Address Versus ................. ..
If the result of this process determines the destination to be a local host, then the computer will simply send the packet on the local subnet. If the result of the comparison determines the destination to be a remote host, then the computer will forward the packet to the default gateway defined in its TCP / IP properties. It is then the responsibility of the router to forward the packet to the correct subnet. TroubleshootingTCP / IP network problems are often caused by incorrect configuration of the three main entries in a computer's TCP / . IP properties By understanding how errors in TCP / IP configuration affect network operations, you can solve many common TCP / IP problems.Incorrect Subnet mask: If a network uses a subnet mask other than the default mask for its address class, and a client Is Still Configured with The Default Subnet Mask for the Address Class, Communication Will Fail To Some Near Networks But Not To Distant Ones. As An Example, IF You Create Four Subnets (Such as in The S ubnetting example) but use the incorrect subnet mask of 255.255.255.0 in your TCP / IP configuration, hosts will not be able to determine that some computers are on different subnets than their own. When this happens, packets destined for hosts on different physical networks that are part of the same Class C address will not be sent to a default gateway for delivery. A common symptom of this is when a computer can communicate with hosts that are on its local network and can talk to all remote networks except those that are NEARBY AND HAVE THE CLASS A, B, OR C Address. TO FIX THIS PROBLEM, JUST Enter The Correct Subnet Mask In The TCP / IP Configuration for That Host.
Incorrect IP Address:. If you put computers with IP addresses that should be on separate subnets on a local network with each other, they will not be able to communicate They will try to send packets to each other through a router that will not be able to forward them correctly. A symptom of this problem is a computer that can talk to hosts on remote networks, but can not communicate with some or all computers on their local network. to correct this problem, make sure all computers on the same physical network have IP addresses on the same IP subnet If you run out of IP addresses on a single network segment, there are solutions that go beyond the scope of this article.Incorrect default Gateway:. A computer configured with an incorrect default gateway will be able to communicate WITH HOSTS ON ITS OWN NETWORK Segment t gateway, a host will be able to communicate with some remote networks, but not others. This problem is common if an organization has a router to an internal TCP / IP network and another router connected to the Internet. REFERENCESTwo popular references on TCP / IP Are:
"TCP / IP ILLUSTRATED, VOLUME 1: The Protocols," Richard Stevens, Addison Wesley, 1994
"Internetworking with TCP / IP, VOLUME 1: Principles, Protocols, And Architecture," DOUGLAS E. COMER, Prentice Hall, 1995
It is strongly recommended that a system administrator responsible for TCP / IP networks have at least one of these references available GlossaryBroadcast address -. An IP address with a host portion that is all ones.
Host - a Computer or Other Device ON A TCP / IP Network.Internet - The Global Collection of NetWorks That Are Connected Together and Share A CommON Range of IP Addresses.
Intern - The Organization RESPONSIBLE for Administration of IP Addresses on the Internet.
IP - The Network Protocol Used for Sending Network Packets over A TCP / IP Network or The Internet.
IP Address - a Unique 32-bit Address for a Host ON A TCP / IP Network OR InternetWork.
NetWork - There Are THIS ARTICLE. ONE IS A Group of Computers ON A Single Physical Network Segment; The Other IS AN IP Network Address Range That Is Allocated by a system administrator.
Network address - An IP address with a host portion That Is All Zeros.
OcTet - An 8-Bit Number, 4 of Which Comprise A 32-Bit IP Address. The the since the decimal value 0- 255.
Packet - a Unit of Data Passed over a TCP / IP Network OR Wide Area Network.
RFC (Request for Comment) - a Document Used to Define Standards on The Internet.
Router - a Device That Passs Network Traffic BetWeen Different IP Networks.
Subnet Mask - a 32-bit number used to distinguish the network and host portions of an ip address.
Subnet OR Subnetwork - A Smaller Network Created by Dividing A Larger Network Into Equal Parts.
TCP / IP - Used Broadly, The Set of Protocols, Standards and Utilities Commonly Used On The Internet and Large Networks.
Wide Area NetWork (WAN) - A Large Network That Is A Collection of Smaller Networks Separated by Routers. The Internet IS AN EXAMPLE OF A VERY LARGE WAN.
Introduction When configuring a TCP / IP protocol on a Microsoft Windows computer, the IP address and subnet mask are required in TCP / IP configuration settings, which typically requires a default gateway.
To properly configure TCP / IP, it is necessary to understand the addressing method of the TCP / IP network and the division of networks and subnets. This article is intended to introduce the concept of IP networks and subnets. This article contains a glossary. More information As the Internet protocol, the success of TCP / IP is largely achieved in its ability to connect different sizes of networks and different types of systems. These networks are forced to define three major classes with predefined sizes (there are other categories), each category can be divided into smaller subnets by system administrators. The subnet mask is used to divide the IP address into two parts. A section identifies the host (computer), and the other part identifies the network it belongs. View IP (Internet Protocol) address and study its organization can help you better understand the IP address and subnet mask. IP Address: Network and host IP addresses are a 32-bit number that uniquely identifies hosts on TCP / IP networks (computers, or other devices such as printers or routers). The IP address is typically represented in dot decimal format, and four numbers are separated by periods, such as 192.168.123.132. To understand how the subnet mask is used to distinguish between different hosts, networks, and subnets, check the IP address represented by binary.
For example, point division decimal IP address 192.168.123.132 is 32 digits in binary representation 1100000000000000000000000000100. The meaning of this number may be difficult to understand, so it is divided into four parts, each of which has eight binary numbers.
These eight parts are called eight groups. The example IP address is turned 11000000.10101000.01111011.10000100. The meaning of this number is just a little bit, so in most applications, the binary address will be converted to the dot decimal format (192.168.123.132). The duty decimal number is an eight-bit group that is converted from binary into a decimal representation.
In order to make TCP / IP WAN (WAN) efficiently in a network set, the router that deliver packets between networks does not know the exact location of the target host of the packet. The router only knows which network of the host is, and uses the information stored in the routing table to determine how to send the data package to the network of the target host. When the packet is transmitted to the target network, the packet is transmitted to the corresponding host.
In order to make this process, the IP address is divided into two parts. The previous part of the IP address is used as the network address, and the latter part is used as the host address. Take 192.168.123.132 as an example, it is divided into these two parts, it will be: 192.168.123. Network .132 Host - or - 192.168.123.0 - Network address. 0.0.0.132 - Host address. The second item of the subnet mask is the subnet mask, which is necessary for TCP / IP. TCP / IP Protocol Use Subnet Mask to determine that the host is in the local subnet or in a remote network.
In TCP / IP, which part of the IP address is used as a network address and host address, so unless you have a detailed information, the above network address and host address cannot be determined. This information is provided in another 32-bit number called subnet mask. In this example, the subnet mask is 255.255.255.0. If you don't know that 255 in the binary representation is equal to 11111111, it may not be aware of the meaning of the number; according to this analysis, the subnet mask is: 111111111.11111111.1111111.0000000, the IP address and subnet mask are arranged together, Dividing the network part and host part of this address: 11000000.10101000.01111011.10000100 - IP address (192.168.123.132) 111111111.11111111111111.111111111111.111111111111.1111111111.1111111111111.1111111111111.00000000 - Subnet mask (25555555.0) before 24 bits (Number 1 in the subnet mask 1) The logo is a network address, and the remaining number of the subnet mask is identified as the host address. According to this: 11000000.10101000.01111011.00000000 - Network address (192.168.123.0) 00000000.00000000.00000000.100000000 - Host address (000.000.000.132) This, we can know that in this example, use 255.255.255.0 subnet mask, The network ID is 192.168.123.0, and the host address is 0.0.0.132. When the packet reaches 192.168.123.0 subnet (from a local subnet or remote network), and its target address is 192.168.123.132, your computer will receive it from the network and process it.
Almost all decimal subnet masks are converted to the left side, all of which are all zero binary numbers on the right side. Some other common subnet masks are: Decimal Binary 255.255.255.192 1111111.11111111.1111111.11000000 255.255.255.224 1111111.11111111.1111111.11100000 Internet RFC 1878 (available from http://www.internic.net) described can be used in TCP / IP networks A effective subnet and subnet mask. The network type Internet address is assigned by the organization of the organization INTERNET (http://www.internic.net). These IP addresses are divided into several classes. The most common of these is A, B and C class. There are also D and E Class, but end users are usually not used. Each address class has a different default subnet mask. The category of the IP address can be identified by viewing the first eight-bit group of the IP address. Below is the scope of the A, B and CTERNET addresses, each of the types of addresses:? The default subnet mask used by Class A network is 255.0.0.0, and the first eight-bit group is 0-127. Address 10.52.36.11 is a Class A address. Its first eight-bit group is 10, between 1 to 126 (including 1 and 126). • The default subnet mask used by Class B network is 255.255.0.0, and the first eight-bit group is 128-191. Address 172.16.52.63 is a B address. Its first eight-bit group is 172, between 128 to 191 (including 128 and 191). • The default subnet mask for C networks is 255.255.255.0, and the first eight-bit group is 192-223. Address 192.168.123.132 is a Class C address. Its first eight-bit group is 192, between 192 to 223 (including 192 and 223). In some cases, the default subnet mask value may not be suitable for institutional needs due to the physical topology of the network or because the number of networks (or hosts) is limited by the default subnet mask. The next part will explain how to use the subnet mask to divide the network. Subnet Configuration System Administrators can further divide A, B or Class Class TCP / IP network or subsequently configured for these networks. When you coordinate the Internet's logical address structure (Abstract World of IP Address and Subnet) to coordinate the physical network used in the real world, the subnet configuration is necessary. System administrators accepted by IP address blocks can manage unconditioned networks with easy in line with these addresses. For example, you have a wide area network that there are 150 hosts in the three networks (located in different cities) in the WAN network. Each network in these three networks has 50 hosts. Assign you Class C network 192.168.123.0. (This address is for convenience of explanation, actually from the range of unallocated in the Internet.) This means that the address 192.168.123.1 to 192.168.123.254 is used for your 150 hosts.
The two addresses that cannot be used in the example are 192.168.123.0 and 192.168.123.255 because the host part is all the binary addresses for one and all zero. The reason for the zero address is to use it to specify the network without specifying the host. 255 Address (all of the host addresses in the binary representation) are used to broadcast messages to each host in the network. Just remember that the first address and the last address in any network or subnet cannot be assigned to any individual host.
Now you should be able to give 254 hosts to the IP address. This operation will be smooth if all 150 computers are in a network. However, your 150 computers are located in three separate physical networks. Without more address blocks for each network, simply divide the network to enable you to use an address block in multiple physical networks. In this case, the network is divided into four subnets using a subnet mask that makes the network address larger and possible host address range. That is, you are "borrow" some of us commonly used for the host address, and use them for the network part of the address. Subnet mask 255.255.255.192 gives you four networks, each network has 62 hosts. This operation can be carried out successfully due to binary representation 255.255.255.192 and 111111111111111111111111111111111111111111110000. The first two digits of the last eight groups becomes a network address, so you get an additional network 00000000 (0), 01000000 (64), 10000000 (128) and 11000000 (192). (Some administrators only use two subnets that will be 255.255.255.192 as the subnet mask. For more information on this topic, see RFC 1878.) In these four networks, the last 6 binary numbers can be used Host address.
Using subnet masks 255.255.255.192, your 192.168.123.0 networks becomes four networks 192.168.123.0, 192.168.123.64, 192.168.123.128 and 192.168.123.192. These four networks would have as valid host addresses: 192.168.123.1-62 192.168.123.65-126 192.168.123.129-190 192.168.123.193-254 retrial again, all the invalid or all zeros of binary host addresses, so you can not Using the last eight-bit group of 0, 63, 64, 127, 128, 191, 192, or 255.
Now, two host addresses 192.168.123.71 and 192.168.123.133, you will learn about its principles. If you use the default C subnet mask 255.255.255.0, both addresses are located in the 192.168.123.0 network. However, if you use subnet masks 255.255.255.192, they are located in different networks; 192.168.123.71 is located in 192.168.123.64, in 192.168.123.128 networks. The default gateway If the TCP / IP computer needs to communicate with the host in another network, it is usually communicated by a device called a router. In TCP / IP terms, the host specified in the host is referred to as the default gateway to the host subnet link to other networks. This section explains how TCP / IP determines whether a packet is sent to its default gateway to reach another computer or device in the network.
When the host attempts to communicate with another device using TCP / IP, it uses the defined subnet mask and the target IP address to compare the subnet mask and its own IP address. This comparison result tells the computer to the local host or a remote host.
If the result of this process determines that the target is a local host, the computer only sends the packet to the local subnet. If the comparison result determines that the target is a remote host, the computer forwards the packet to the default gateway defined in its TCP / IP property. Then, the router is responsible for forwarding the packet to the correct subnet. Troubleshooting TCP / IP network issues are usually caused by error configurations of three main entries from the computer's TCP / IP properties. Understand how the error in the TCP / IP configuration affects the network operation, you can solve many common TCP / IP issues.
Error subnet mask: If the network will use other subnet masks outside the default mask for its address classes, and the client still uses the default subnet mask of the address class to configure it, you can communicate with the remote network. But you cannot communicate with some nearby networks. For example, if you create four subnets (eg, in the subnet configuration example), the host will not be able to determine if some computers are in the same computer in the TCP / IP configuration. Net different subnet. When this happens, the packet sent to the host in different physical networks as part of the same Class C address will not be transmitted to the default gateway. The common symptoms of this problem are to communicate with hosts and all remote networks in their local network, but cannot communicate with the location of the same A, B or C address. To resolve this issue, just enter the correct subnet mask in the TCP / IP configuration of the host. Error IP Address: If you put together the IP addresses in different subnets of the local network, they cannot communicate. They will try to send packets with each other through the router, and the router cannot forward these packets correctly. The symptom of this problem is that the computer can communicate with hosts in the remote network, but cannot communicate with some or all of the computer in its local network. To resolve this issue, make sure that all computers in the same physical network have IP addresses in the same IP subnet. If the IP address in a network segment is run, you can also use some solutions to process, but it has exceeded the scope of this article.
Error Default Gate: The computer configured with the error can communicate with the host in its own network segment, but cannot communicate with the hosts in some or all remote networks. If a physical network has multiple routers, and the error router is configured as the default gateway, the host can communicate with some remote networks, but cannot communicate with other remote networks. If there is a router in the organization to connect to the internal TCP / IP network, another router is connected to the Internet, which is common. The two common references in TCP / IP are:
"TCP / IP ILLUSTRATED, VOLUME 1: The Protocols", Richard Stevens, Addison Wesley, 1994
"Internetworking with TCP / IP, Volume 1: Principles, Protocols, And Architecture", Douglas E. COMER, Prentice Hall, 1995
It is recommended to use the system administrator responsible for the TCP / IP network to use at least one of the references. Glossary Broadcast Address - The host part is all IP addresses.
Computers or other devices in the host - TCP / IP network.
Internet - Global Network Collection connecting together and sharing a public range of IP addresses.
InterNic - responsible for managing the IP address in the Internet.
IP - Network protocol for sending network packets on a TCP / IP network or Internet.
IP address - The unique 32-bit address of the TCP / IP network or Internet host.
Network - In this article, the word "network" has two meanings. One meanings refers to a computer set on a single physical network segment, and another meaning refers to the range of IP network addresses allocated by the system administrator.
Network address - The host part is all zero IP addresses.
Eight groups - an 8-digit number, 4 eight-bit groups constitute a 32-bit IP address. Their ranges are 00000000-11111111, corresponding to the decimal value 0- 255.
Packets - Data units transmitted through TCP / IP networks or wide area networks.
RFC (Request for Comment) - Documentation for defining the Internet standard.
Router - Transport network communication between different IP networks. Subnet mask - a 32-bit number for distinguishing the network part and the host part of the IP address.
Subnet - The smaller network created by dividing the larger network into equal parts.
TCP / IP - The collection of protocols, standards, and utilities that are typically widely used in Internet and large networks.
WAN (WAN) - large network, which is a collection of smaller networks separated by routers. For example, the Internet is a very large WAN.
