Slash notation can be used to define the size of an IP network. Slash notation use a number following a forward slash to indicate the number of bits that are reserved for the network portion of the IP address. The number following the forward slash indicate the number of bits that the network uses to define itself.
The remainder of the bits within the 32-bit IP address are available to be allotted to individual devices on the network. A larger number defined following the forward slash indicates that more bits are to be used to define the network. Thus, there are fewer bits available to be allotted to individual devices on the network.
Slash Notation for IP Addresses
A larger number following the forward slash indicates fewer IP address are available for those individual devices. A smaller number following the forward slash indicate that the network uses fewer bits to define itself. Thus, there are more bits available to be allotted to individual devices on the network.
A smaller number following the forward slash indicates more IP addresses are available for those individual devices. Slash notation replaced the old classful system that was used to assign IP addresses to networks. Under the old classful system, each network was assigned a specific number of IP addresses.
Because the number of addresses assigned to each network was fixed, many times the devices connected to that network did not fully utilize those addresses. Slash notation allow networks to use only as many addresses as they require to assign to each device. Because slash notation allows networks to use only the addresses that they require, it help to prevent the exhaustion of the available IPv4 addresses.
Slash notation can be seen in action within a typical home network. Many home routers is assigned an IP address and a slash prefix. For instance, one example is a home router with an IP address of 192.168.1.0 with a /24 prefix.
The /24 prefix means that 24 bits of the IP address are to be reserved for the network. That leaves 8 bits of the IP address to be allotted to individual devices on that network. The first IP address that can be assigned to a device in this example is the address that is used to identify the network itself.
The last IP address that can be assigned to a device is used to broadcast a message to all the devices on the network. Thus, the first and last address in this range of IP addresses cannot be assigned to any device. The number of devices that can be on the network is calculated by taking the number of available bits in the IP address (in this instance 8 bits) and plugging those values into the following formula: 2to the power of the available bits minus 2.
In large networks, numerous device must be able to connect to the network. Large networks may use larger prefixes in the slash notation system. However, larger prefixes for large networks can create issue with the routing tables of those networks.
Routing tables contain the routes for all the networks and subnets in a range. Large routing tables can slow the performance of the internet. In order to prevent routing tables from becoming too large, network prefixes can be aggregated.
Prefix aggregation is the process of grouping many small subnets into one large, aggregated subnet that is advertised to routers in the internet. For instance, instead of advertising four separate subnets in the routing table, they can be aggregated to form one large, continuous advertisement. This will reduce the routing table from four entries to one.
Smaller prefixes has other uses on the internet, as. For instance, smaller prefixes can be used for WAN (Wide Area Network) links between two routers. Only two devices will be using the addresses on these networks, so a small prefix is appropriate.
Furthermore, a small prefix can also be used to identify only one specific machine on the network. This can be useful in tasks like creating firewall rules to allow only specific machines to have access to the network, or assigning a loopback address to one of the device on the network. There are trade-offs in using various size of prefixes.
For instance, using many small network subnets will allow for more security in a network. However, this will also place more of a workload on the routers. Using fewer, larger subnets will make it easier to manage a network.
However, this will expose the network to more risks of broadcast storm. Based off the needs of the network, the size of the prefixes can be selected. Additionally, prefix aggregation can be used to increase the efficiency of a network whenever it is possible to do so.