Saving Public IPs with CIDR and NAT
AWS Chapter 1.4 - CIDR, NAT RFC1918, Subnetting
While both NAT (Network Address Translation) and CIDR (Classless Inter-Domain Routing) were introduced in part to address the shortage of IPv4 public IP addresses. However, they serve different functions, provide distinct benefits, and arose from different needs.
Here's a deeper look into each, their benefits beyond IP conservation, and the stories behind their creation.
CIDR (Classless Inter-Domain Routing)
Purpose and Benefits
IP Address Conservation: CIDR allows IP address ranges to be allocated based on precise network needs, rather than sticking to rigid classes (A, B, C). This flexibility conserves IP addresses by avoiding the waste seen in class-based addressing.
Efficient Routing: CIDR reduces the number of routes in a network's routing table. With CIDR, multiple IP address ranges can be aggregated (or "supernetted") into a single route, simplifying routing tables and improving routing efficiency.
Flexibility: CIDR allows organizations to request exactly the amount of IP space they need, which is more adaptable as networks grow or shrink.
Story Behind CIDR's Creation
In the early days of the internet, the class-based IP addressing scheme led to significant inefficiencies and waste. Large blocks of IPs (Class A) were often underused, while smaller blocks (Class C) quickly ran out of addresses. This inflexible allocation led to a crisis in the 1990s as IPv4 address exhaustion became a real concern.
CIDR was introduced in 1993 to address this issue by removing the rigid class structure and enabling more granular allocation through subnetting. CIDR made it possible to define networks with prefixes (like /24), specifying exactly how many IPs a network should have. By allowing more efficient use of IP space, CIDR helped delay IPv4 exhaustion and optimized routing processes, contributing to a more scalable and manageable internet.
The Birth of CIDR and the Need for Subnetting
CIDR allowed for flexible, classless allocation of IP addresses, did away with fixed classes, letting administrators define network sizes by choosing a prefix length, like 192.168.1.0/24. This flexibility allowed ISPs and organizations to request only as many IPs as they needed, conserving valuable address space.
Enter Subnetting
With CIDR came a revelation: if we can split up the internet’s address space into smaller, flexible blocks, why not split our own networks too? This idea led to subnetting.
Subnetting is a technique that lets us divide a larger network into smaller, more manageable pieces (subnets), each with its own IP range. Think of subnetting as dividing a big plot of land into smaller, custom-sized lots for different types of buildings (departments, teams, or zones) to maximize the use of available space.
Here’s how it works:
Say a company has a 192.168.1.0/24 network, which offers 256 IP addresses.
Instead of using this single network for all devices, the company can subnet it. For example, they could split it into two /25 subnets (each with 128 IP addresses) to allocate to different departments or floors.
Subnetting became an invaluable tool for network administrators. It allowed them to design networks that matched their organizational structure, control IP usage, and improve network performance by limiting the number of devices in each subnet.
Benefits of Subnetting
Efficient IP Management: Subnetting prevents IP waste by allowing precise allocation. Organizations can assign IP addresses based on the actual needs of each department or branch.
Network Performance and Security: By keeping devices in separate subnets, network traffic can be isolated, reducing congestion. Additionally, subnetting creates smaller “islands” within the network, which can help contain security threats or outages.
Easier Troubleshooting: With subnetting, each department or building floor has its own range, making it easier to troubleshoot network issues without affecting the entire organization.
Scalability: Subnetting allows networks to grow in a structured way. When more devices are added, administrators can simply create additional subnets without needing to redesign the whole network.
In Summary
CIDR: Created to improve IP address allocation and routing efficiency, using variable-length prefixes to eliminate rigid IP classes.
CIDR led to subnetting by showing the world that IP address allocation could be flexible and efficient. Subnetting then built on that flexibility, enabling network administrators to carve out sub-networks that perfectly fit their organizational needs. Together, CIDR and subnetting transformed network design, making it scalable, efficient, and adaptable to the ever-growing demands of the internet age.
NAT (Network Address Translation)
Purpose and Benefits
IP Address Conservation: NAT allows multiple devices on a private network to share a single public IP address, effectively conserving public IPv4 addresses. This is especially useful for home networks, corporate offices, and any environment with numerous devices.
Security: NAT provides a basic level of security by hiding internal IP addresses from the outside world. External entities only see the public IP of the NAT device (e.g., a router), making it harder to directly reach devices within the private network.
Network Flexibility and Scalability: NAT enables internal networks to use private IP addresses (in the ranges defined by RFC 1918), allowing easy expansion without the need to obtain additional public IP addresses.
Story Behind NAT's Creation
NAT emerged as a practical solution in the mid-1990s as the number of devices connecting to the internet grew exponentially. Companies and households were using internal networks with multiple devices, but IPv4 space limitations meant they couldn’t get enough public IP addresses to assign one to each device.
With NAT, a single public IP could be shared among all devices on a local network by translating private IP addresses to a public IP when traffic goes out to the internet. This translation effectively extends the life of IPv4 by allowing more devices to connect to the internet with fewer public IPs, solving the immediate demand for addresses and providing an extra layer of security by isolating internal network addresses.
RFC 1918 and NATing
Imagine it’s the 1990s, and the internet is growing faster than anyone expected. Offices, homes, and universities are all connecting their devices, and suddenly there’s a problem: not enough IP addresses to go around! The IPv4 address pool, designed years before, is running out, and it’s clear that not every device can have its own unique public IP.
So, the internet community gathers to find a solution, and that’s where RFC 1918 comes into play. Think of RFC 1918 as a clever hack to save IP addresses by setting aside special “neighborhoods” of addresses that can be reused privately by anyone, anywhere, as long as they stay within their own network.
Here’s the deal: RFC 1918 defines three ranges of IP addresses, like gated communities, for internal use only:
10.0.0.0 to 10.255.255.255 – A huge range for big private networks.
172.16.0.0 to 172.31.255.255 – A medium-sized range.
192.168.0.0 to 192.168.255.255 – A smaller range, popular in homes and small offices.
These addresses can be used by anyone without needing to register them. So, businesses, homes, and campuses can all have devices with the same private IP addresses without any conflict, as long as those devices don’t need to directly connect to the public internet.
Here’s the twist: when devices using these private addresses want to access the internet, NAT (Network Address Translation) steps in to translate their private IPs to a public one, like a middleman. This way, RFC 1918, combined with NAT, helps the world continue connecting without running out of public IP addresses.
RFC 1918 was a lifesaver for the early internet, allowing for massive internal networks without eating into the precious supply of public IPs. This "private IP plan" is still the backbone of nearly every home and business network today, letting us all connect to the internet with ease and efficiency.
Commonalities and Differences between CIDR and NAT
Commonalities:
1 Address Conservation: Both CIDR and NAT were introduced to conserve IPv4 addresses due to increasing demand.
2 IPv4 Exhaustion Solution: Each technology addressed the IPv4 scarcity crisis from a different angle: CIDR by making address allocation more efficient, and NAT by enabling shared access to public IPs.
Differences:
Functionality: CIDR optimizes IP address allocation and routing efficiency, while NAT translates private IPs to a single public IP for external communication.
Use Case: CIDR is primarily a tool for ISPs and large organizations needing precise IP allocations and routing optimizations, while NAT is more commonly used by routers in local networks, like homes and offices
Summary
NAT: Created to enable private networks to share a single public IP address, helping to extend IPv4 usability and offering basic security benefits.
NAT Relies on the RFC1918 to define the private, non routable subnets and the IP Addresses that can reside behind the NAT Gateway.
⠀Together, CIDR and NAT significantly delayed IPv4 exhaustion and made the modern internet’s growth more manageable. They’re complementary solutions: CIDR addresses routing efficiency and scalable IP allocation, while NAT solves the challenge of limited public IPs for large networks.
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