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Point To Point Link Addressing Calculator

Work out point to point link addressing instantly with clear inputs, formula shown and shareable results.

About Point To Point Link Addressing Calculator

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.

Formula

Link addressing

addresses = links x per-link (2 for /31 or /127, 4 for /30); covering prefix = 32 - ceil(log2(addresses))

Worked example

With the default values below, Point To Point Link Addressing Calculator returns Addresses needed for all links of 48. Change any input above and every figure here is recalculated in your browser.

Inputs used

Number of point-to-point linksminimum 1
24
Addressing styleone of /31 - RFC 3021, two addresses per link, /30 - classic, four addresses per link, IPv6 /127 per link
/31 - RFC 3021, two addresses per link

Results

Addresses needed for all links
48
Addresses consumed per link
2
Prefix that covers the whole allocation
26 /n
Addresses wasted on network/broadcast
0

Step by step

  1. 1Values used
  2. 2Link addressing
  3. 3Addresses needed for all links= 48
  4. 4Addresses consumed per link= 2
  5. 5Prefix that covers the whole allocation= 26 /n
  6. 6Addresses wasted on network/broadcast= 0

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is a /31 safe on all platforms?

Modern router operating systems support it on routed interfaces. Avoid it where a broadcast-dependent protocol or an older switch SVI is involved.

Why not use /64 per IPv6 link?

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.

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