Introduction
IPv6 is often described as simpler than IPv4, yet many people feel the opposite when they first encounter real subnet calculations. A prefix like 2001:bd8:1010:a500::/54 can look intimidating, especially if you are used to neat boundaries such as /48 or /64.
This article explains how to calculate the full IPv6 range for 2001:bd8:1010:a500::/54 without guesswork. The goal is not only to show the correct result, but to help you understand why that result is correct, so you can repeat the process confidently with any similar IPv6 prefix.
Understanding the IPv6 address structure
An IPv6 address is 128 bits long. These bits are written as eight hexadecimal blocks, called hextets, separated by colons. Each hextet represents 16 bits, which means eight hextets together make up the full 128-bit address.
When written in its expanded form, the address looks like this:
2001:bd8:1010:a500:0000:0000:0000:0000
The :: symbol is simply a shortcut. It replaces one or more consecutive hextets that contain only zeros. This shorthand makes IPv6 addresses easier to read but can hide important details when doing calculations, so expanding the address is always a good first step.
What the /54 prefix really means
The /54 at the end of the address is the prefix length. It tells you how many bits from the left are fixed as the network portion.
In this case:
The first 54 bits are fixed
The remaining 74 bits are variable
These variable bits are what define the size of the range and how many subnets can exist inside it. The tricky part with /54 is that 54 is not divisible by 16, so the prefix boundary does not line up neatly with a hextet boundary.
Locating the prefix boundary
Each hextet contains 16 bits.
The first 3 hextets account for 48 bits
That leaves 6 more bits to reach the /54 boundary
This means:
Hextets 1 through 3 are completely fixed
The first 6 bits of the 4th hextet are fixed
The remaining 10 bits of the 4th hextet are variable
Hextets 5 through 8 are fully variable
Understanding this split is the most important part of calculating the range correctly.
Breaking down the fourth hextet
The fourth hextet in the address is a500.
Converted to binary, it looks like this:
1010 0101 0000 0000
Since only the first 6 bits are part of the prefix, those bits stay fixed. The remaining 10 bits can change.
Visually, that looks like this:
101001 xxxxxxxxxx
Those ten variable bits can represent 1024 different values, because 2¹⁰ equals 1024. This fact becomes important when we look at subnet counts later.
Calculating the start of the range
To find the first address in an IPv6 range, you set all variable bits to zero.
In this case:
The first 54 bits remain exactly as defined
The remaining 74 bits are set to zero
That gives you:
2001:bd8:1010:a500::
This is the starting address of the /54 range.
Calculating the end of the range
To calculate the last address, you do the opposite. All variable bits are set to one.
That means:
The 10 variable bits in the 4th hextet are all set to 1
Hextets 5 through 8 become
ffff
When you apply this correctly, the fourth hextet reaches a53f.
So the final address in the range is:
2001:bd8:1010:a53f:ffff:ffff:ffff:ffff
This value represents the absolute upper limit of the /54 block.
The full /54 range explained clearly
Putting it together, the complete IPv6 range for this prefix is:
First address:
2001:bd8:1010:a500::Last address:
2001:bd8:1010:a53f:ffff:ffff:ffff:ffff
Everything between those two values is included in the /54 network.
How many /64 subnets are inside this /54
IPv6 networks almost always use /64 subnets for individual LANs. This is not arbitrary. Many IPv6 mechanisms expect a 64-bit interface identifier.
The number of /64 subnets inside a /54 is calculated like this:
2^(64 − 54) = 2¹⁰ = 1024
So 2001:bd8:1010:a500::/54 contains 1024 separate /64 subnets.
Examples include:
2001:bd8:1010:a500::/642001:bd8:1010:a501::/64…
2001:bd8:1010:a53f::/64
This makes a /54 extremely useful for structured, scalable network designs.
Why the fourth hextet stops at a53f
This result often raises questions.
The reason the range ends at a53f is because only the last 10 bits of that hextet are allowed to change. Once those bits reach their maximum value, the prefix boundary is exceeded.
Trying to calculate this by simply adding hexadecimal values can easily lead to errors. The safest method is always:
Identify how many bits are fixed
Identify how many bits are variable
Set variable bits to all zeros for the start
Set variable bits to all ones for the end
Common mistakes to avoid
Many incorrect calculations come from a few repeated misunderstandings.
One common mistake is assuming the prefix boundary aligns with a full hextet. With /54, it does not.
Another is treating IPv6 like IPv4 and trying to apply familiar broadcast logic. IPv6 works differently, even though the idea of a numerical range still applies.
A third mistake is working only in hexadecimal without checking which bits are actually variable. Bit-level awareness is essential for odd prefix lengths.
Verifying your calculation
Even when you understand the math, verification is a good habit. Subnet calculators can confirm your start and end addresses and help catch typing mistakes.
However, calculators should support your understanding, not replace it. When you know how the calculation works, you are far less likely to misconfigure routing, firewall rules, or address plans.
Real-world use of a /54 IPv6 prefix
A /54 is commonly used in structured environments.
Service providers may allocate a /54 to organizations that need room to grow without jumping straight to a /48.
Enterprises often use a /54 to divide networks cleanly by building, department, or function, assigning one /64 per VLAN.
Labs, test environments, and segmented infrastructures also benefit from the flexibility of having over a thousand /64 networks available.
Final summary
Here is the result one last time, clearly stated:
Prefix: 2001:bd8:1010:a500::/54
Range start: 2001:bd8:1010:a500::
Range end: 2001:bd8:1010:a53f:ffff:ffff:ffff:ffff
Once you understand where the /54 boundary falls and how many bits are variable, the calculation becomes logical and repeatable. This approach removes guesswork and gives you confidence when working with IPv6 networks of any size.
