[GUIDE] How IPv6 Delegation Works

[Anime4000]

How IPv6 Delegation Works

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IPv6 delegation can be confusing at first, especially for users transitioning from IPv4 networking. This post explains how DHCPv6-PD, Router Advertisement (RA), and SLAAC work together in a modern IPv6 deployment.

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Basic Flow

1. ISP/BNG provides IPv6 connectivity
2. Router receives WAN IPv6 address
3. Router receives delegated IPv6 prefix block
4. Router advertises subnet to LAN
5. Clients generate their own IPv6 addresses

Key Components

RA (Router Advertisement)

• Provides gateway information
• Provides subnet information
• Allows devices to discover IPv6 router automatically

DHCPv6-PD (Prefix Delegation)

• Delegates an IPv6 prefix block to the router
• Example: /56 or /60
• Router can split this into multiple LAN subnets

SLAAC (Stateless Address Autoconfiguration)

• Client devices automatically generate their own IPv6 address
• No traditional DHCP lease required for end devices
• Works using Router Advertisements

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Example Topology

ISP/BNG delegates:

Code: Select all

2402:4e20:b00b:8000::/56

Router then assigns LAN subnet:

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2402:4e20:b00b:8000::/64

Client devices automatically generate addresses such as:

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2402:4e20:b00b:8000:dead:ffff:feed:cafe/64
2402:4e20:b00b:8000:dead:ffff:feed:beef/64
2402:4e20:b00b:8000:dead:ffff:feed:f00d/64

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Important Notes

Without DHCPv6-PD, LAN devices may not receive globally routable IPv6 connectivity properly.

Some possible workarounds include:

• Using NAT66 (generally discouraged)
• Using NDP proxy (can increase neighbor table usage on ISP side)

Proper DHCPv6-PD deployment is the recommended modern solution.

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Common Prefix Sizes

• /64 = Single LAN subnet
• /60 = 16x /64 subnets
• /56 = 256x /64 subnets
• /48 = 65,536x /64 subnets

IPv6 was designed to avoid address exhaustion problems common in IPv4, allowing proper subnetting and end-to-end connectivity.

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Notes for MikroTik Users

Typical setup:

• DHCPv6 Client requests prefix delegation
• IPv6 Pool generated from delegated prefix
• LAN interface advertises subnet via RA
• Clients configure themselves automatically

This is the most common modern IPv6 deployment method for HomeLab and ISP environments.

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Credits

2402:4e20::/32 address by Perfect Network.

Feedback and corrections are welcome.