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IPv6 Addresses - Expansion

IPv6 address expansion reverses the compression process by restoring omitted zeros and replacing double-colon notation with the full hextet groups it represents. This skill is essential for correctly interpreting and working with compressed IPv6 addresses.

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About this video

IPv6 addresses are often written in compressed form to improve readability, but working with them in certain technical contexts requires knowing how to restore the full address. Expansion is the reverse of compression: leading zeros that were dropped from individual hextets must be added back, and any double-colon notation must be replaced with the correct number of all-zero hextet groups. Determining how many hextets a double colon represents depends on counting the existing hextets in the address and subtracting from the required total of eight. Once that count is established, the missing groups can be filled in to reconstruct the complete 128-bit address. Accurate IPv6 expansion is a foundational networking skill, as the full address format is required for tasks such as subnetting, routing table analysis, and firewall rule configuration. Consistent practice with varied examples builds the speed and precision needed to perform this conversion reliably under real-world conditions.

What you'll learn

What's covered

IPv6 Address Expansion

Aligned to

Cisco CCNA
1.9 Describe IPv6 address types
1.8 Configure and verify IPv6 addressing and prefix
Cisco CCST Networking
2.3 Identify IPv6 addresses and prefix formats
CompTIA Network+
3.4 Given a scenario, implement IPv4 and IPv6 network services

Key terms

IP Address
A numerical label assigned to each device connected to a network that uses the Internet Protocol.
Internet Protocol
IP
The principal communications protocol for routing packets across network boundaries.
IPv6
The sixth version of the Internet Protocol, using 128-bit addresses written in hexadecimal and separated by colons to provide a vastly larger address space than IPv4's 32-bit addresses. IPv6 also introduces built-in features like SLAAC, NDP, and mandatory support for IPsec.
Hextet
A group of four hexadecimal digits in an IPv6 address; eight hextets separated by colons form a complete 128-bit IPv6 address.
Double-Colon Notation
An IPv6 compression rule represented by '::' that replaces one or more consecutive all-zero 16-bit groups, usable only once per address.
Leading Zero
A zero that precedes the significant digits within a hextet of an IPv6 address, which may be suppressed in compressed notation and must be restored during expansion.

Transcript

We compressed an IPv6 address and removed those zeros, but how do we figure out what the full IPv6 address is by putting the zeros back in?

Here's a list of compressed addresses over here. Let's go ahead and expand them. What I'm going to do first of all is figure out where that double colon is at, and figure out how many that is representing. So if I count this: one, two, three, four, five, six — there are six hextets, so that's representing two hextets. I know that there's going to be two of them there. Once I've done that, then I just can fill in the rest of the zeros here.

So 2001, colon — it's missing a zero there, I know there's four characters there — so 0db8, colon, 0000, colon, 85a3. And then here's where that double colon is at, so I know those are two hextets, so I'll do one and two. And then finish it off: 8a2e, and then add one more zero there for that last one.

Here's a series of different IPv6 addresses. Figure out what the expanded version of all of them is, and then check your work.

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