Work out point to point link addressing instantly with clear inputs, formula shown and shareable results.
A routed link between two interfaces only needs two addresses. A classic /30 spends four per link and throws away half, while an RFC 3021 /31 uses both addresses and halves consumption. In IPv6 the equivalent convention is a /127 per link, carved from a /64 reserved for infrastructure.
Link addressing
addresses = links x per-link (2 for /31 or /127, 4 for /30); covering prefix = 32 - ceil(log2(addresses))
Modern router operating systems support it on routed interfaces. Avoid it where a broadcast-dependent protocol or an older switch SVI is involved.
It works but wastes an enormous amount of space and exposes the link to neighbour-cache exhaustion. RFC 6164 recommends /127 for inter-router links.