IPv6 Practice Test 2026 – Complete Exam Prep

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Why are /64 subnets used per link in IPv6 addressing best practices?

/128; Each host gets a single address to maximize uniqueness.

/48; To allocate large number of subnets per site.

/64; SLAAC-based addressing requires a 64-bit network prefix to generate the interface identifier deterministically.

In IPv6, a /64 per link is used because address construction on a link relies on a 64-bit network prefix combined with a 64-bit interface identifier. This setup enables Stateless Address Autoconfiguration (SLAAC): a device on the link can automatically generate its own address by pairing the link’s 64-bit prefix with a 64-bit interface ID derived from its hardware address or created randomly for privacy. The result is a huge address space on each link (2^64 addresses), making autoconfiguration simple and scalable without needing a DHCP server.

If you used a /128 on a link, there would be only one address per link, which defeats autoconfiguration and scalability. A /48 is intended for site-wide aggregation, not per-link addressing. A /32 is the provider-facing prefix, not the per-link subnet. So a /64 per link best supports SLAAC and practical networking on IPv6 LANs.

/32; To simplify routing tables.