What is an IP address?
An IP address (Internet Protocol address) is a numerical label assigned to every device on a network. It's how devices find and communicate with each other — similar to a postal address, but for network traffic. Without an IP address, a device has no logical identity on the network.
There are currently two versions of IP in use: IPv4, the original standard that most people are familiar with, and IPv6, the newer version designed to solve IPv4's biggest limitation — it's running out of addresses.
What the addresses look like
The most immediately obvious difference between IPv4 and IPv6 is the format. IPv4 addresses are short and familiar. IPv6 addresses are long, written in hexadecimal, and look intimidating at first — but the format has a clear logic to it.
IPv4 uses 32 bits split into four groups of 8 bits (octets), each written as a decimal number from 0–255. IPv6 uses 128 bits split into eight groups of 16 bits, each written as four hexadecimal characters separated by colons.
IPv6 addresses can be shortened using two rules the exam tests:
Rule 1 — Drop leading zeros: 0db8 becomes db8 — leading zeros in any group can be omitted.
Rule 2 — Collapse consecutive all-zero groups with "::": A sequence of groups that are all zeros can be replaced with :: — but only once per address. That's why 2001:0db8:0000:0000:0000:0000:0370:7334 can be written as 2001:db8::370:7334.
Why IPv6 exists — the address exhaustion problem
IPv4 was designed in 1981, when the internet was a small research network. Nobody anticipated that billions of phones, laptops, servers, smart TVs, and IoT devices would eventually need unique addresses.
IPv4 has ~4.3 billion possible addresses. We used them all.
To cope, the industry deployed workarounds like NAT (Network Address Translation) — which lets many devices share a single public IPv4 address. NAT bought time, but it added complexity and broke certain applications. IPv6 solves the problem at the root by providing an astronomically larger address space.
IPv6's 128-bit address space provides approximately 340 undecillion unique addresses — that's 340 followed by 36 zeros. There are enough IPv6 addresses to assign trillions of addresses to every grain of sand on Earth. Running out is not a realistic concern.
IPv4 vs IPv6 — full comparison
| IPv4 | IPv6 | |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Format | 192.168.1.1 (decimal) | 2001:db8::1 (hex) |
| Total addresses | ~4.3 billion | 340 undecillion |
| Address config | Manual or DHCP | Manual, DHCPv6, or SLAAC* |
| NAT required? | Yes (address shortage) | No — every device gets a public address |
| Header complexity | Variable (options field) | Simplified fixed header |
| Broadcast? | Yes (255.255.255.255) | No — uses multicast instead |
| Loopback address | 127.0.0.1 | ::1 |
| Introduced | 1981 | 1998 |
* SLAAC (Stateless Address Autoconfiguration) lets IPv6 devices configure their own address without a DHCP server, using the network prefix and their own MAC address.
Important IPv4 address ranges to know
Not all IPv4 addresses are used the same way. The exam tests several reserved ranges you need to recognize on sight.
ping 127.0.0.1. Traffic never leaves the device.Important IPv6 address types
::1 — IPv6 loopback. The compressed form of all zeros with a final 1. Equivalent to 127.0.0.1.
fe80::/10 — Link-local. Every IPv6 interface gets one automatically. Not routable. Starts with fe80.
Addresses starting with 2 or 3 — Global unicast (public). Routable on the internet.
Special addresses cheat sheet
Do both versions run at the same time?
Yes — most networks today run dual-stack, meaning devices have both an IPv4 and an IPv6 address simultaneously. Your Windows machine almost certainly has both right now. Run ipconfig /all and you'll see both listed under each adapter — an IPv4 address in the familiar 192.168.x.x format and an IPv6 address starting with fe80 (link-local) or a longer global address.
The transition from IPv4 to IPv6 has been gradual and is still ongoing. IPv4 won't disappear overnight — the exam reflects this by testing both, and real-world networks will run dual-stack for years to come.
Key Takeaways
IPv6 Transition Mechanisms — Network+ Deep Dive
The Network+ exam tests how organisations migrate from IPv4 to IPv6. Three transition mechanisms appear regularly: dual stack, tunnelling, and NAT64/translation.
| Mechanism | How It Works | Exam Key Fact |
|---|---|---|
| Dual Stack | Device runs both IPv4 and IPv6 simultaneously — uses whichever is appropriate per destination | Preferred method — most common in enterprise migration. Both stacks fully operational. |
| 6to4 Tunnelling | Encapsulates IPv6 packets inside IPv4 packets to cross IPv4-only infrastructure | IPv6 traffic treated as payload — used when IPv6-only islands need to communicate across IPv4 network |
| Teredo | Tunnels IPv6 over UDP/IPv4 — works through NAT devices | Microsoft-developed; used when 6to4 fails behind NAT. Port 3544. |
| NAT64 | Translates between IPv6 and IPv4 at the network boundary | Allows IPv6-only clients to reach IPv4 servers — used in mobile networks |
| ISATAP | Intra-Site Automatic Tunnel Addressing Protocol — tunnels IPv6 over IPv4 within a site | Embeds IPv4 address in IPv6 address; less common than dual stack |
IPv6 Address Configuration Methods
| Method | How It Works | Exam Note |
|---|---|---|
| Static | Manually configured IPv6 address | Used for servers and infrastructure devices |
| DHCPv6 (Stateful) | DHCPv6 server assigns address and tracks leases | Like DHCP for IPv4 — full control over assignments |
| SLAAC | Stateless Address Autoconfiguration — device generates its own address from prefix in Router Advertisement + EUI-64 or random | No DHCP server needed — router advertises /64 prefix, device self-configures. Privacy extensions randomise the interface ID. |
| DHCPv6 (Stateless) | SLAAC for address + DHCPv6 for DNS/options only | Hybrid — router provides prefix, DHCPv6 provides DNS servers |
FF:FE is inserted in the middle, and bit 7 is flipped. Result: a globally unique interface ID. Privacy extensions generate a random interface ID instead to prevent tracking.
IPv4 and IPv6 Security Considerations — Security+
Security+ tests security implications specific to each protocol version. IPv6 introduces new attack surfaces that many organisations overlook during migration.
| Topic | IPv4 | IPv6 |
|---|---|---|
| IPsec | Optional — added as extension | Mandatory in spec (though often not enforced in practice) |
| NAT | Used everywhere — hides internal addresses | Not used — every device has public address (privacy concern) |
| ARP spoofing | ARP used to resolve IP→MAC | NDP (Neighbour Discovery Protocol) replaces ARP — NDP spoofing is equivalent attack |
| Broadcast | Broadcast traffic exists — used for ARP, DHCP | No broadcast — uses multicast instead (reduces attack surface) |
| Rogue RA attack | N/A | Attacker sends fake Router Advertisements to hijack SLAAC — devices configure wrong gateway |
| Tunnel security | N/A | 6to4 and Teredo tunnels can bypass IPv4 firewall rules if not explicitly filtered |
Network+ and Security+ Exam Scenarios
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