/127s for IPv6 Point -To-Point links

/127s for IPv6 Point -To-Point links

/127’s for point-to-point links (RFC 6164) instead of /64’s


[RFC4291] specifies that interface IDs for all unicast addresses,
except those that start with the binary value 000, are required to be
64 bits long and to be constructed in Modified EUI-64 format. In
addition, it defines the Subnet-Router anycast address, which is
intended to be used for applications where a node needs to
communicate with any one of the set of routers on a link.

Some operators have been using 127-bit prefixes, but this has been
discouraged due to conflicts with Subnet-Router anycast [RFC3627].
However, using 64-bit prefixes creates security issues that are
particularly problematic on inter-router links, and there are other
valid reasons to use prefixes longer than 64 bits, in particular /127
(see Section 5).
   This document provides a rationale for using 127-bit prefix lengths,
reevaluates the reasons why doing so was considered harmful, and
specifies how /127 prefixes can be used on inter-router links
configured for use as point-to-point links.
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