3.4 Given a scenario, implement IPv4 and IPv6 network services
Dynamic Addressing
📘CompTIA Network+ (N10-009)
1. What is SLAAC?
SLAAC is a method used in IPv6 networks to automatically assign IP addresses to devices without needing a central server like DHCP. It allows a device (like a computer, server, or printer) to configure its own IPv6 address automatically when it connects to a network.
Key points:
- Stateless: There’s no central database keeping track of which IPs are assigned. The device configures itself.
- Autoconfiguration: The device automatically creates its own IP address using information from the network.
Think of it as your device saying: “I know the network prefix, so I’ll make up my own address to communicate.”
2. How SLAAC Works – Step by Step
When a device connects to an IPv6 network using SLAAC, this happens:
Step 1: Link-Local Address
- Every IPv6 device automatically generates a link-local address.
- This address always starts with FE80::/10 and is used to communicate on the local network segment.
- It ensures that the device can talk to other devices even before getting a global IPv6 address.
Step 2: Router Advertisement (RA)
- Routers on the network periodically send Router Advertisement messages.
- These messages include:
- The network prefix (the first part of the IPv6 address)
- Information about whether devices should use SLAAC, DHCPv6, or both
- Devices use this information to generate their own global IPv6 address.
Step 3: Generating the Global IPv6 Address
- The device combines:
- The network prefix from the router
- Its interface identifier (usually based on its MAC address, or a randomly generated ID for privacy)
- This creates a unique IPv6 address that can communicate across the network.
Step 4: Duplicate Address Detection (DAD)
- Before using the new IPv6 address, the device checks if any other device on the network is already using it.
- If there’s a conflict, the device generates a new address.
- This ensures every IPv6 address on the network is unique.
3. SLAAC vs DHCPv6
It’s important to know the difference for the exam:
| Feature | SLAAC | DHCPv6 |
|---|---|---|
| Server required? | No | Yes |
| State maintained? | No (stateless) | Yes (stateful) |
| IP assignment? | Device generates itself | Server assigns |
| Other info (DNS, gateway)? | Usually requires RA options or separate DHCPv6 | Server provides |
💡 On many networks, SLAAC and DHCPv6 can work together:
- SLAAC gives the IP address automatically
- DHCPv6 can provide extra info like DNS servers
4. Key Exam Concepts
Students should remember the following points for SLAAC:
- SLAAC is IPv6 only – not used in IPv4.
- Devices use RA messages from routers to get network information.
- Addresses are self-generated – no DHCP server needed.
- Link-local addresses are always present.
- Duplicate Address Detection (DAD) prevents address conflicts.
- SLAAC can be combined with DHCPv6 for additional info.
5. IT Environment Example
Here’s how SLAAC is used in a real network:
- A new server is plugged into a company network.
- The server automatically generates a link-local address (FE80::1…).
- The router sends a RA message with the network prefix 2001:db8:10:1::/64.
- The server combines the prefix with its interface ID and becomes 2001:db8:10:1::abcd.
- The server checks the network (DAD) – no duplicates. Address is now valid and ready to use.
- Optionally, a DHCPv6 server tells the server to use 2001:4860:4860::8888 as its DNS server.
No admin had to manually assign an IP – the device did it automatically.
6. SLAAC Benefits
- Easy deployment: Devices can join the network without admin intervention.
- Scalable: Works well in large networks.
- Reduced administrative overhead: No need to maintain a DHCP server for addresses.
7. SLAAC Limitations
- Limited control: Admins can’t force a specific IP for each device.
- DNS info may need DHCPv6: SLAAC alone doesn’t provide all configuration info.
- Privacy concerns: Using MAC-based interface IDs can make devices trackable.
✅ Exam Tip:
If a question mentions IPv6, automatic IP assignment, and no DHCP server, the correct answer is SLAAC. Always remember: RA → prefix → self-generated address → DAD → ready to use.
