CCNA | P4: IPv4 Addressing | C1: Perspectives on IPv4 Subnetting
IPv4 subnetting is an amazing technique that can help you optimize your network resources, improve network performance, enhance security, and simplify network management! It is a fundamental concept that plays a critical role in network design and maintenance.
Lesson Contents
- Intro to IPv4
- History of IPv4
- Purpose of IPv4
- IPv4 Address Space
- Need for Subnetting
- What is a Subnet?
- What is Subnetting ?
- Benefits of Subnetting
- Conclusion
Intro to IPv4
IPv4 is the primary version of the Internet Protocol, a 32-bit address that identifies the network, host and subnet of a device on the internet.
It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks.
IPv4 was the first version deployed for production on SATNET in 1982 and on the ARPANET in January 1983.
It is still used to route most Internet traffic today, even with the ongoing deployment of Internet Protocol version 6 (IPv6), its successor.
IPv4 uses a 32-bit address space which provides 4,294,967,296 (232) unique addresses, but large blocks are reserved for special networking purposes.
It has features such as encryption, fragmentation, multicasting and VLSM. It also has advantages such as security, scalability and system management.
IPv4 is a connectionless protocol, and operates on a best-effort delivery model, in that it does not guarantee delivery, nor does it assure proper sequencing or avoidance of duplicate delivery. These aspects, including data integrity, are addressed by an upper layer transport protocol, such as the Transmission Control Protocol (TCP). Click here to learn more about TCP/IP Protocol in one of post in CCNA series.
History of IPv4
The history of IPv4 dates back to the early 1980s when it was developed as a part of the ARPANET project, funded by the United States Department of Defense. The protocol was described in IETF publication RFC 791 (September 1981), replacing an earlier definition of January 1980 (RFC 760) . In March 1982, the US Department of Defense decided on the Internet Protocol Suite (TCP/IP) as the standard for all military computer networking.
Purpose of IPv4
The purpose of IPv4 is to define and enable internetworking at the internet layer of the Internet Protocol Suite. In essence, it forms the Internet.
It uses a logical addressing system and performs routing, which is the forwarding of packets from a source host to the next router that is one hop closer to the intended destination host on another network.
IPv4 Address Space
IPv4 reserves special address blocks for private networks (~18 million addresses) and multicast addresses (~270 million addresses).
IPv4 addresses may be represented in any notation expressing a 32-bit integer value. They are most often written in dot-decimal notation, which consists of four octets of the address expressed individually in decimal numbers and separated by periods .
For example, the loopback address 127.0.0.1 was commonly written as 127.1, given that it belongs to a class-A network with eight bits for the network mask and 24 bits for the host number.
When fewer than four numbers were specified in the address in dotted notation, the last value was treated as an integer of as many bytes as are required to fill out the address to four octets. Thus, the address 127.65530 is equivalent to 127.0.255.250.
Need for Subnetting
In the original design of IPv4, an IP address was divided into two parts: 1. The network identifier was the most significant octet of the address
2. The host identifier was the rest of the address.
The latter was also called the rest field. This structure permitted a maximum of 256 network identifiers, which was quickly found to be inadequate.
To overcome this limit, the most-significant address octet was redefined in 1981 to create network classes, in a system which later became known as classful networking.
The revised system defined five classes. Classes A, B, and C had different bit lengths for network identification. The rest of the address was used as previously to identify a host within a network.
Because of the different sizes of fields in different classes, each network class had a different capacity for addressing hosts. In addition to the three classes for addressing hosts, Class D was defined for multicast addressing and Class E was reserved for future applications.
What is a Subnet?
A subnet is a logical subdivision of an IP network. Computers that belong to the same subnet are addressed with an identical group of its most-significant bits of their IP addresses.
What is Subnetting ?
Subnetting is the process of dividing a network into smaller networks called subnets. Computers that belong to the same subnet are addressed with an identical group of its most-significant bits of their IP addresses.
This results in the logical division of an IP address into two fields: the network number or routing prefix, and the rest field or host identifier. The rest field is an identifier for a specific host or network interface.
The routing prefix may be expressed as the first address of a network, written in Classless Inter-Domain Routing (CIDR) notation, followed by a slash character (/), and ending with the bit-length of the prefix.
For example, 198.51.100.0/24 is the prefix of the Internet Protocol version 4 network starting at the given address, having 24 bits allocated for the network prefix, and the remaining 8 bits reserved for host addressing.
Addresses in the range 198.51.100.0 to 198.51.100.255 belong to this network, with 198.51.100.255 as the subnet broadcast address.
The IPv6 address specification 2001:db8::/32 is a large address block with 296 addresses, having a 32-bit routing prefix.
For IPv4, a network may also be characterized by its subnet mask or netmask, which is the bitmask that, when applied by a bitwise AND operation to any IP address in the network, yields the routing prefix. Subnet masks are also expressed in dot-decimal notation like an IP address.
For example, the prefix 198.51.100.0/24 would have the subnet mask 255.255.255.0.
Traffic is exchanged between subnets through routers when the routing prefixes of the source address and the destination address differ. A router serves as a logical or physical boundary between the subnets.
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Benefits of Subnetting
Subnetting an existing network has various benefits that vary with each deployment scenario.
In the address allocation architecture of the Internet using CIDR and in large organizations, efficient allocation of address space is necessary.
Subnetting may also enhance routing efficiency, or have advantages in network management when subnets are administratively controlled by different entities in a larger organization.
Subnets may be arranged logically in a hierarchical architecture, partitioning an organization’s network address space into a tree-like routing structure, or other structures, such as meshes.
Conclusion
To Summarize subnetting is a powerful technique that can help you optimize your network resources, improve network performance, enhance security, and simplify network management.
It allows for better management of network resources and more efficient routing of traffic.
Subnetting an existing network has various benefits that vary with each deployment scenario.
It can control the rapid exhaustion of IP addresses to some extent, enhance routing efficiency, or have advantages in network management when subnets are administratively controlled by different entities in a larger organization.
Subnets may be arranged logically in a hierarchical architecture, partitioning an organization’s network address space into a tree-like routing structure, or other structures, such as meshes.
Happy subnetting! 🌐👨💻
