This article will provide you need to configure basic information for your router as routing IP, such as how the address is divided and how branch subnet works. You will learn the only subnet in the router to allocate each interface IP address with a unique subnet. And don't worry, let's show you a lot of examples to help relation. For more information on file conventions before you start, see Cisco Technical Tips. Prerequisites This document does not have special prerequisites. The components used are not limited to specific software and hardware versions. Other information If the definition is helpful, let you start some vocabulary. Address - Unique number ID is assigned to a host or interface in the network. Subnet - Share a part of the network of a specific subnet address. Subnet mask - part of the address refers to the subnet and partially refers to the 32-bit combination of the host once described. Interface - network connection. If you have received your legal address from the Internet (Internet Network Information Center), you are ready to start. If the connection is not planned to the Internet, we strongly recommend that you use the reservation address from RFC 1918. Understanding the IP address IP address is an address unique to identify a device in an IP network. The address can be a can be divided into the network portion and the host portion consisting of 32 binary locations with a subnet mask. 32 binary bits are divided into four eight-bit groups (1 eight-bit group = 8 bits). Each eight-bit group is converted into a decimal and is previously separated in one sentence (small point). To this end, IP addresses are considered to be expressed in dotted decimal format (eg, 172.16.81.100). Value in each octacular group from 0 to 255 decimal or 00000000 - 11111111 binary. This is how binary eight-bit groups turn into ten credits: the rightmost bit, or the minimum effective bit, the eight-bit group will indicate the value of 20. The bit will indicate the value of 21 on the left. This continues until the leftmost bit, or the maximum active bit, the value is 27. Thus, if the binary bit is that, the corresponding decimal number is 255 as shown below. 1 1 1 1 1 1 1 1 128 64 32 16 8 4 2 1 (128 64 32 16 8 4 2 1 = 255) This is an example eight-bit conversion when not all bits set to 1 Time. 0 1 0 0 0 0 0 1 0 64 0 0 0 0 0 1 (0 64 0 0 0 0 0 1 = 65) and this is the IP address representative of the example display in binary and decimal. 10. 1. 23. 19 (DECIMAL) 00001010.000000011.00010111.00010011 (binary) These eight-bit groups are divided into addressing schemes that adapt to large and small networks. There are five different types of networks, A to E. This paper focuses on addressing groups A to C, as groups D and E are backup and discuss that they are outside the scope of this article. Note: And note the terms "Class C, Class B" and, etc. Are used herein to help achieve IP addressing and subnet division. These terms are rarely used in the industry due to the latter (CIDR) in the uncoated domain. A IP address is given, and the group can be determined from three high order. The following is displayed in three high-order and divided into address ranges for each group. Displayed for information purposes, class D and E-class addresses. At Class A address, the first eight-bit group is a network part, so the example above the A class has a primary network address of 10. The eight-bit groups 2, 3 and 4 (lower 24 bits) are to be separated by the network manager into a subnet and the host when she adapts. Class A address is a network of more than 65,536 hosts (actually, 16,581,375 hosts!). At class B address, the first two eight-bit groups are network part, so the examples of the B class have a primary network address of 172.16. The eight-bit groups 3 and 4 (16 bits) are for local subnets and hosts. Class B address is available between 256 and 65,536 hosts. At Class C Address, the first three eight-bit groups are network parts. The example above Class C has a major network address to 193.18.9.
The eight-bit group 4 (8-bit) is for local subnets and hosts - for networks with less than 256 hosts. Network mask Network mask helps you know which part of the address of the address identifies the network and which partial identification node. Class A, B and C have default masks, also known as natural masks, as shown below. Class A: 255.0.0.0 Class C: 255.255.0.0 Class C: 255.255.255.0 IP Address Class A network of unburred subnets will have an Address / Mask to similar to: 8.20.15.1 255.0.0.0. Discover the mask to help you identify the network and node parts of the address, the conversion address, and the mask into binary number. 8.20.15.1 = 00001000.00010100.00001111.00000001 255.0.0.0 = 11111111.0000000000.00000000.000000 Once the arrangement address and mask are indicated in binary, then identifying the network and host IDs easier. There is a corresponding mask bit to 1 represent any address bits of the network ID. There is a corresponding mask bit set to the 0 table show any address bits of the node ID. 8.20.15.1 = 0000001000.00010100.00001111.00000001 255.0.0.0 = 111111111111.000000000000000000.00000000 --------------------- Net ID | Host ID Netid = 00001000 = 8 Hostid = 00010100.00001111.0000000100.00001111.00000001 = 20.15.1 Understanding Subsidiary PETs Allows you to create multiple logical networks existing within a single A, B or C network. If you don't branch, you can only use a network from your Class A, B or C network, is unrealistic. Each data link must have a unique network ID in the network, with each node is a member of the same network. If you interrupt a major network (Class A, B or C) into a smaller subnet, you allow you to create an internet subsystem. Each data link is here online and will have a unique network / subnetory ID. All devices or gateways, connected N network / subnets have n obvious IP addresses, one for interconnect each network / subnet. Branch subnet network, use certain bits to expand the natural mask from the host ID section of the address. For example, a Class C network 204.15.5.5, which is a natural mask is 255.255.255.0, and you can create subnets in the following ways. 204.15.5.0 - 10101100.00001111.00000101.0000000000 255.255.255.224 - 11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111) --------------------------- | SUB | The code is 255.255.255.224, you get three (see as "Sub") from the original host part of the address and use them to work. It is possible to create eight subnets with these three bits. With the remaining five host ID, each subnet can have 32 host addresses, 30 may actually allocate to the device because all zero host IDs or all parts are not allowed (it is very important to remember this). So, given this, the following subnets were created.
204.15.5.0 255.255.255.224 host address range 1 to 30 204.15.5.32 255.255.255.224 host address range 33 to 62 204.15.5.64 255.255.255.224 host address range 65 to 94 204.15.5.96 255.255.255.224 host address range 96 to 126 204.15. 5.128 255.255.255.224 host address range 129 to 158 204.15.5.160 255.255.255.224 host address range 161 to 190 204.15.5.192 255.255.255.224 host address range 193 to 222 204.15.5.224 255.255.255.224 host address range 225 to 254 Note: there are two The method represents the above mask. First of all, because you use three more than the "Nature" Class C class, you can indicate that these addresses are 3-bit subnet mask. Alternatively, the second, the mask is 255.255.255.224 may also also indicate that it is / 27 despite the 27 bits set in the mask. This second method uses with CIDR. Using this method, one of the above networks can be described with symbol prefix / length. For example, 204.15.5.32 / 27 representation of the network 204.15.5.32 255.255.255.224. When appropriate for Prefix / Length symbol indicates that the mask is in the rest of this article. Using the above network subnet mechanism, eight subnets are allowed, and the network may appear as shown below. Note that each of the upper routers are attached to four sub-networks, and a subnet is common to two routers. Also, each router has an IP address as each subnet attached. Each sub-network can potentially support 30 host addresses. This brings an interesting point. The more the host is used for the subnet mask, more you have a subnet available. However, multi-branch subnets are available, and fewer host addresses can be used for each subnet. For example, Class C network 204.17.5.0 and mask are 255.255.255.224 (/ 27) Allow you to have eight subnets, each with 32 host addresses (30. If you use a mask 255.255. 255.240 (/ 28), are divided. 204.15.5.0 - 10101100.com, China, Sub | --- Because you have four subnets now, you only have four left-to-host addresses. You can have 16 subnets in this case, where each can have 16 host addresses (14 can Assigned to the device). Take a look at how the network is in the Class B network. If there is a network 172.16.0.0, you know that its natural mask is 255.255.0.0 or 172.16.0.0.0/16. Expand the mask to anything 255.255.0.0 means you branch subnet. You can quickly find that you create a subnet C network Class C network than the above capabilities. If you use a mask 255.255.248.0 (/ 21), how many parts of the net and host Is this allowed? 172.16.0 - 10101100.000000000000000000.00000000 255.255.248.0 - 111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 )- - You use five origin from the original host. This will allow you to have 32 subnets (25). After using the five digits for subnet, you are left to 11-bit as host addresses.
This will allow each subnet therefore have 2048 host addresses (211), 2046 may be assigned to the device. Note: From now, there is limited to use subnet 0 (all subnets are adjusted to zero) and all partial branch subnets (all subnet are set to one). Some devices are not allowed to use these subnets. When configuring, the Cisco system device will allow these subnet IP Subnet ZERO commands. Example Exercise 1 is clear that you have a understanding of the subnet, place this knowledge to use. In this case, you generate two address / mask combinations, the following written with Prefix / Length symbol, assigned to two devices. Your task is to determine if these devices are in the same subnet or different subnets. You can do this by using each device address and mask to determine which subnet each address belongs to. DeviceA: 172.16.17.30/20 DeviceB: 172.16.28.15/20 determine subnet DeviceA: 172.16.17.30 - 10101100.00010000.00010001.00011110 255.255.240.0 - 11111111.11111111.11110000.00000000 ---------------- - | SUB | ------------ Subnet = 10101100.00010000.00010000.00000000 = 172.16.16.0 Viewing a corresponding mask bit set to one address bits and adjust all other address bits to zero ( This is equal to between mask and address as the execution logic "and" is equal to which of the subnets. In this case, Devicea belongs to the subnet 172.16.16.0. Determining the subnets for Deviceb: 172.16.28.15 - 10101100.000111 255.255.240 - 1111111111111111111111111111111111110000.00000000 ------------------- - Subnet = 10101100.00010000.00010000.00000000 = 172.16.16.0 So from the above, Devicea and Deviceb are the address of the same subnet. Example Exercise 2 Make Class C Network 204.15.5.0/24, branch subnet network In order to create the following network with displayed host needs. View the above network, you can find that you ask you to create five subnets. The largest subnet must support 28 host addresses. This may be with Class C network? As if you have, how is it? You can start by looking at the subnet requirements. In order to create you will need to use three necessary subnets from the Class C host bit. Two will only give you four subnets (22). Because you need three subnets, leave you five-bit host parties. How many mains will be supported? 25 = 32 (30 available). This meets the requirements. So you are sure that you create the above network and Class C networks. Example How do you might allocate a subsystem as follows: Neta: 204.15.5.07 Host Address Range 1 to 30 Netb: 204.15.5.32/27 host address range 33 to 62 Netc: 204.15.5.64/27 host address range 65 to 94 NETD: 204.15.5.96/27 Host Address Range 97 To 126 Nete: 204.15.5.128/27 Host Address Range 129 To 158 VLSM Sample Tmalic Subnet Division Previous Example You Note The same subnet mask is applicable to all subnets. This means that each subnet has the same number of host addresses available. You may have need this in some cases, but in many cases, there is a similar subnet mask to all subnets cause a waste address space.
For example, at the second exercise of the above, C networks are split into eight phase-equivalent large sizes; however, each subnet does not use all available host addresses, resulting in wasteful address space. This can be imaged as follows: View the image above, you can find the subnet, Neta, Netc, and NetD have many unused host address spaces. This may be a deliberate design accounting for the future growth, but in many cases this is a waste of address space due to such a fact that the same subnet mask is used for all subnets. Variable Length Subnet Mask (VLSM) allows you to use different masks for each subnet to efficiently use address space. VLSM examples If network and needs and demand use VLSM to develop a subnet mechanism using VLSM in an example exercise 2. In the case of the following: Neta: Must Support 28 Hosts Netc: Must Support 2 Hosts Netd: Must Support 7 Hosts Netd: Must Support 28 Host determines what mask will recognize the required number of hosts. Neta: Requires A / 28 (255.255.255.240) Mask to Support 14 Hosts Netb: Requires A / 27 (255.255.255.224) Mask to Support 28 Hosts Netc: Requires A / 30 (25555555.252) Mask to Support 2 Hosts Netd * : requires a / 28 (255.255.255.240) mask to support 7 hosts netE: requires a / 27 (255.255.255.224 mask to support 28 hosts * a / 29 (255.255.255.248) would only allow 6 usable host addresses therefore netD requires a / 28 Mask. The easiest way to allocate the subnet will begin to allocate the biggest one. So you can assign the following ways. Netb: 204.15.5.0/27 Host Address Range 1 To 30 Nete: 204.15.5.32/27 Host Address Range 33 To 62 Neta: 204.15.5.64/28 Host Address Range 65 To 78 Netd: 204.15.5.80/28 Hostc: 204.15.5.96/30 Host Address Range 97 To 98 This can be represented by graphics as follows. From the above Image You can find half of the address space to find the helpful VLSM save. CIDR Introducing unbeatable within the Internet (CIDR) Improved address space utilization and routing scalability. It is required for the internet in Internet router The rapid growth and growth of IP routing tables. CIDR moves from traditional IP classes (Class C, Class C, Class C, etc.). In CIDR, IP network is represented by the prefix, is the length of the IP address and mask Sign. The length means it is set to a maximum of the leftmost continuous mask bit. Network 172.16.0.0 255.255.0.0 can be shown as 172.16.0.0/16. CIDR also represents a more hierarchical Internet architecture, each Domain adopt its IP address from a higher level . This allows the domain summary to perform at a higher level. For example, if the ISP has a network 172.16.0.0.0/16, then ISP can provide users with 172.16.1.0/24, 172.16.2.0/24, etc. However, when making an advertisement to other providers, only ISP needs to do notices 172.16.0.0/16. For more information on CIDR, see RFC 1518 and RFC 1519.
