Why is fe80::/10 reserved for link local addresses when fe80::/64 is actually used?

  • I understand that IPv6 reserves the fe80::/10 prefix for link local addresses, and that hosts select an address with a /64 prefix.

    Why is the reserved space so much larger than what is actually used for link local?

  • I think the link-local scope was set to /10 simply to "fit in" better with the other scopes, e.g. site-local (before it was replaced with unique local).

    Initially I had thought maybe it was to allow the use of many link-local networks on the same link, but RFC 4291 explicitly states that only fe80::/64 may be used.

    Is there any significance regarding SLAAC implementation? ...is SLAAC "prefix agnostic"?

    SLAAC requires a /64, but it is not really relevant here, because link-local addresses aren't assigned by SLAAC - in fact, SLAAC relies on already having a link-local address.

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Content dated before 7/24/2021 11:53 AM