Proper Address: IPv4 vs. IPv6

Ah, the 1980s. It brought us such classics as Ghostbusters, The Princess Bride, Tina Turner's triumphant comeback, Pac-Man, and the original Apple Macintosh. Also, it gave us the birth of the internet, in which we figured out how to make all our computers one giant, powerful network held together initially by internet protocols (IPs) and, eventually, by a mutual love of cat videos.

Now, each of our devices that connect to the internet require a way to find and send information back and forth, which means they need an IP address. Most folks don't type IP addresses into their search bar though-we use domain names (for example, www.backblaze.com). Which IP addresses correspond to which domain names is stored in a hierarchical and distributed database system known as the domain name system (DNS), which is also an internet protocol.

Today, let's talk about IP addresses: What are IPv4 and IPv6, why is IPv6 necessary, and what impact will it have on networking?

Let's set the scene

Any time you're sending and receiving data, be it a letter in the mail, dialing a phone number, or loading a website, you've got to have an identifiable address reach the proper person and/or device. What all of these types of addresses have in common is that as our population has exploded, we've had to re-work how addresses work in order to include more possible data locations. U.S. zip codes were established in 1963. Area codes were established in 1947, and a great expansion was necessary only three(ish) decades later, and that plan was implemented starting in the late 1980s and ending in the mid '90s.

IP addresses, meanwhile, have been operating on the first and only protocol we introduced in the 1980s, called IPv4. Not only has the world population almost doubled since then, but there has also been a nonlinear explosion in internet-connected devices per person. When IP addresses were first invented, it was unfathomable that most folks would be walking around with a computer in their pocket, remotely checking who's ringing their doorbells while adjusting their thermostat in anticipation of returning home. All of those internet-connected devices use an IP address, in one way or another.

So, it's no surprise that we're now seeing an adoption of a new IP address standard. In keeping with tradition, the versions aren't sequential: Right now we're jumping from IPv4 to IPv6. (What happened to IPv5? It was skipped, sort of.)

What is IPv4?

IPv4 is an internet protocol that assigns addresses to devices. It uses a 32-bit address, represented by four numbers (octets), each between 0 and 255, separated by dots (e.g., 192.168.1.100), and uses decimal notation.

Remember that each bit represents one of two possible values, a 0 or a 1. So, for a 32-bit value, there are 2^32 possible addresses, or 4,294,967,296 IP addresses total. Several IPv4 address blocks were also reserved for private networks and multicast addresses, about 286 million total. Between the two reserved blocks of addresses, that's about 7% of the total addresses in existence.

What is IPv6?

IPv6 uses a 128-bit address, represented by a longer string of numbers and letters (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334) in hexadecimal code, aka hex code. If you've ever designed a MySpace page (hi, Tom!) or a webpage, you're likely familiar with the hex codes used to identify precise colors.

Doing the math as we did above, there are 2^128 possible IPv6 addresses, which is 340 undecillion. (That's the 11th order of magnitude if you're going, million, billion, trillion, and so on.) And, just like IPv4, there are some reserved addresses, but they represent such a comparatively smaller number of total available addresses that it's not even worth calculating a percentage.

Woah, how have we been surviving in the meantime?

We mentioned above that we've known we're running out of IP addresses for a while. But, important detail: There was evidence of the problem as early as 1981, and mitigation efforts were enacted by 1992. Before we get into what mitigation strategies have been used over the years, a bit of a refinement of the above information-IP addresses consist of two main parts, one that identifies the network (or, sometimes, the subnet) and the host, or the destination on that network. (That's true of both IPv4 and IPv6.)

Classful networking

In the original iteration of IPv4, the bits that identified the subnet were fixed, and that meant a lot of wasted space. In 1981, we implemented classful networking. Instead of keeping a fixed number of bits to identify a network, the three most significant bits identified the size of the network prefix, and that sent you to different classes. That meant that existing addresses didn't have to change. Here's a handy table:

Class	Most significant bits	Network prefix size (bits)	Host identifier size (bits)	Address range	Maximum number of networks	Maximum number of hosts per network
A	0	8	24	0.0.0.0-127.255.255.255	128 networks	16,777,216 hosts per network
B	10	16	16	128.0.0.0-191.255.255.255	16,384 networks	65,386 hosts per network
C	110	24	8	192.0.0.0-223.255.255.255	2,097,152 networks	256 hosts per network
D (multicast) E (reserved)	1110 1111	--	--	224.0.0.0-255.255.255.255	--	--

All that sounds a bit like gobbley-gook. An analogy: You live in a city that wants to improve mail delivery, so it's introduced the option to choose from a small, medium, or large mailbox. The sizes are actually pretty disproportionate-the small is about the size of a toaster, whereas the medium is the size of a kitchen trash can. (And large is the size of your car. Who gets that much mail?) No matter which size mailbox you (or your neighbor) chooses, your physical address didn't change when this system was implemented. You usually get more mail than the toaster would accommodate, but never even come close to filling your trash can-sized mailbox. So, that extra space just sits empty and unused, never fulfilling its mail volume potential.

Note that classful networking is now largely defunct, replaced by…

Classless inter-domain routing (CIDR)

The biggest issue of the above system was its inflexibility. Adding classes gave us more flexibility than the original design, but you were still restricted to 8, 16, or 24 bits to identify the network. That means you can end up with a lot of unused IP addresses, as indicated by our above analogy. Here's the math behind why:

The number of addresses available on a network is the inverse of how many bits you use to define it. So, in a 32-bit address, if you use 16 bits to define the network, you have 8 bits leftover to define the host. That's our Class C network, which contained 2^8 (256) IP addresses-not enough for most use cases. And, the next smallest subset, Class B, represented 2^16 IP addresses (65,536 total), which most organizations could not use efficiently. After DNS became the norm, it became clear that classful networking wasn't scalable, and thus CIDR rose to prominence.

CIDR is based on variable-length subnet masking (VLSM), which lets each network be divided into subnetworks of various power-of-two sizes. This method optimizes the allocation of IPv4 addresses by allowing for more flexible address blocks.

Using our analogy, instead of assigning mailbox size based on household size, you might just have a system in which folks walk up to the post office and find their name on a list associated with a mailbox. If someone has more or less mail that month, then they can be assigned the properly sized mailbox.

Network address translation (NAT)

NAT allows multiple devices to share a single public IPv4 address by modifying the IP header when it's in transit. This is super useful when you're talking about private networks-you can assign a single IP address to multiple devices. For example, if you have several internet of thing (IoT) devices in your home, they can all appear to the public network as one IP address, and your local network can figure out what traffic goes where. It also makes it so that if a network moves, the host doesn't necessarily have to be assigned a new IP address, such as if an internet provider like Cox decides to stop doing business in your region, and Spectrum takes over their IP address allocation-though likely they'd just change your public IP address in that specific scenario.

In our mail analogy, NAT is like those group mailboxes you see in rural areas, apartment buildings, or in neighborhoods. Everyone in the same location gets their mail delivered to the same physical address, and your box number is used to further identify your house within the group mailbox.

The secondary market of IP addresses

If we can learn anything from the above workarounds, flexibility and possibility is key. So, it's unsurprising to know that a secondary market has cropped up, introducing things like address recycling, address trading, and address leasing. IPv6 will solve the scarcity issue-but what else can it do?

What are the benefits of IPv6?

So far we've talked about the primary benefit of IPv6-more IP addresses that we clearly need. But, there are other benefits as well. Here's a summary:

Improved Efficiency

• Simpler header: The IPv6 header is simpler than IPv4's, leading to faster packet processing and reduced overhead.
• Efficient routing: IPv6's design allows for more efficient routing, potentially reducing latency and improving network performance. Arguably, most folks won't see a huge performance improvement unless they reconfigure their own network architecture, but the possibility is there.
• Autoconfiguration: IPv6 supports automatic configuration of network interfaces, simplifying setup and reducing administrative overhead.

Enhanced Security

• Built-in security features: IPv6 offers built-in security mechanisms like IPsec, potentially providing better protection against attacks. In practice, it's not typically implemented as most encryption is typically handled at the transport layer security (TLS) IP layer.

Quality of Service (QoS)

• Improved QoS: IPv6 provides better support for QoS, allowing for prioritization of different types of traffic, ensuring a better user experience for applications like video conferencing and online gaming.

Other Benefits

• Reduced reliance on NAT: IPv6 reduces the need for NAT, simplifying network configurations and improving end-to-end connectivity.
• Support for new services: IPv6 is better suited for emerging technologies and applications that require a large number of addresses and advanced features.

What's next? Will we run out again?

Given the amount of addresses for IPv4 vs. IPv6 (4.2 billion vs. 340 undecillion, respectively), you can understand how we might have needed to shore up our IPv4 addresses. Honestly, if you assume one device per person, we already outnumber IPv4 addresses-in fact, we outnumbered IP addresses in the 1970s, before IPv4 was even invented! You shouldn't assume one device per person, by the way. While many countries with widespread broadband access have several devices per person-in the U.S., Consumer Affairs was reporting 21 per U.S. household in 2023, and the average U.S. household for that same year was 2.51 people. Globally, that same source reports 3.6 internet-connected devices per person.

Changes like this can certainly be disruptive, but the good news on that front is that most devices will be dual-stacked for quite a while. That means that you'll have both versions of an IP address, and this change can roll out organically (so to speak). In the end, we'll have a better-performing internet, ready to grow with us for the foreseeable future.

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