IPv4 is the most common network addressing architecture used, though the use of IPv6 has been growing since An IP address is comprised of a network number routing prefix and a rest field host identifier. A rest field is an identifier that is specific to a given host or network interface. CIDR is a method used to create unique identifiers for networks, as well as individual devices.
Note : Also note that the terms "Class A, Class B" and so on are used in this document in order to help facilitate the understanding of IP addressing and subnetting. These terms are rarely used in the industry anymore because of the introduction of classless interdomain routing CIDR. Given an IP address, its class can be determined from the three high-order bits the three left-most bits in the first octet.
Figure 1 shows the significance in the three high order bits and the range of addresses that fall into each class. For informational purposes, Class D and Class E addresses are also shown. In a Class A address, the first octet is the network portion, so the Class A example in Figure 1 has a major network address of 1.
Class A addresses are used for networks that have more than 65, hosts actually, up to hosts! In a Class B address, the first two octets are the network portion, so the Class B example in Figure 1 has a major network address of Octets 3 and 4 16 bits are for local subnets and hosts.
Class B addresses are used for networks that have between and hosts. In a Class C address, the first three octets are the network portion. The Class C example in Figure 1 has a major network address of Octet 4 8 bits is for local subnets and hosts - perfect for networks with less than hosts.
A network mask helps you know which portion of the address identifies the network and which portion of the address identifies the node. Class A, B, and C networks have default masks, also known as natural masks, as shown here:.
In order to see how the mask helps you identify the network and node parts of the address, convert the address and mask to binary numbers. Once you have the address and the mask represented in binary, then identification of the network and host ID is easier.
Any address bits which have corresponding mask bits set to 1 represent the network ID. Any address bits that have corresponding mask bits set to 0 represent the node ID.
Subnetting allows you to create multiple logical networks that exist within a single Class A, B, or C network. If you do not subnet, you are only able to use one network from your Class A, B, or C network, which is unrealistic.
Each data link on a network must have a unique network ID, with every node on that link being a member of the same network. If you break a major network Class A, B, or C into smaller subnetworks, it allows you to create a network of interconnecting subnetworks.
In order to subnet a network, extend the natural mask with some of the bits from the host ID portion of the address in order to create a subnetwork ID. For example, given a Class C network of By extending the mask to be With these three bits, it is possible to create eight subnets.
With the remaining five host ID bits, each subnet can have up to 32 host addresses, 30 of which can actually be assigned to a device since host ids of all zeros or all ones are not allowed it is very important to remember this. So, with this in mind, these subnets have been created. Note : There are two ways to denote these masks. First, since you use three bits more than the "natural" Class C mask, you can denote these addresses as having a 3-bit subnet mask.
Or, secondly, the mask of This second method is used with CIDR. For example, The network subnetting scheme in this section allows for eight subnets, and the network might appear as:.
Notice that each of the routers in Figure 2 is attached to four subnetworks, one subnetwork is common to both routers. Also, each router has an IP address for each subnetwork to which it is attached. Each subnetwork could potentially support up to 30 host addresses. This brings up an interesting point.
The more host bits you use for a subnet mask, the more subnets you have available. However, the more subnets available, the less host addresses available per subnet. For example, a Class C network of If you use a mask of Since you now have four bits to make subnets with, you only have four bits left for host addresses.
So in this case you can have up to 16 subnets, each of which can have up to 16 host addresses 14 of which can be assigned to devices. Take a look at how a Class B network might be subnetted.
If you have network Extending the mask to anything beyond You can quickly see that you have the ability to create a lot more subnets than with the Class C network. You use five bits from the original host bits for subnets. This allows you to have 32 subnets 2 5.
After using the five bits for subnetting, you are left with 11 bits for host addresses. Our fully managed colocation services make use of data centres across the UK, to securely house your network equipment. Posted on: 25th September More services to help We offer a comprehensive range of IT services to suit all businesses - from "helpdesk"-style IT support to data centre hosting services. Technical Services From ad hoc projects to ongoing, proactive support contracts, deeserve can plug into your department any time to provide specialist server and network management.
Data Centre Our fully managed colocation services make use of data centres across the UK, to securely house your network equipment. Want to work with us?
0コメント