IPv6 calculator

Subnet details, /127 and /128 planning, splitting, compress/expand, overlap check.

What it is for

From a chosen pool (often a /64 for P2P) generate correct /127 pairs or /128 host rows.

Why it helps

Avoid fake /127 on odd bases (::1, ::3…) and wasted address space; see Side A/B and slot numbering instantly.

Pool and mode

Hex sequence

After ::9 → ::a, after ::f → ::10. /127 uses even base only.

::0::1::2::3::4::5::6::7::8::9::a::b::c::d::e::f::10::11::1a::1b::20

Results

Network2001:db8:1:ffff::/64
Addresses18446744073709551616
Slots9223372036854775808
Mode/127
# Subnet Side A Side B Note
0 2001:db8:1:ffff::/127 2001:db8:1:ffff:: 2001:db8:1:ffff::1 Pair #0 · …:0
1 2001:db8:1:ffff::2/127 2001:db8:1:ffff::2 2001:db8:1:ffff::3 Pair #1 · …:2
2 2001:db8:1:ffff::4/127 2001:db8:1:ffff::4 2001:db8:1:ffff::5 Pair #2 · …:4
3 2001:db8:1:ffff::6/127 2001:db8:1:ffff::6 2001:db8:1:ffff::7 Pair #3 · …:6
4 2001:db8:1:ffff::8/127 2001:db8:1:ffff::8 2001:db8:1:ffff::9 Pair #4 · …:8
5 2001:db8:1:ffff::a/127 2001:db8:1:ffff::a 2001:db8:1:ffff::b Pair #5 · …:a
6 2001:db8:1:ffff::c/127 2001:db8:1:ffff::c 2001:db8:1:ffff::d Pair #6 · …:c
7 2001:db8:1:ffff::e/127 2001:db8:1:ffff::e 2001:db8:1:ffff::f Pair #7 · …:e
8 2001:db8:1:ffff::10/127 2001:db8:1:ffff::10 2001:db8:1:ffff::11 Pair #8 · …:10
9 2001:db8:1:ffff::12/127 2001:db8:1:ffff::12 2001:db8:1:ffff::13 Pair #9 · …:12
10 2001:db8:1:ffff::14/127 2001:db8:1:ffff::14 2001:db8:1:ffff::15 Pair #10 · …:14
11 2001:db8:1:ffff::16/127 2001:db8:1:ffff::16 2001:db8:1:ffff::17 Pair #11 · …:16
12 2001:db8:1:ffff::18/127 2001:db8:1:ffff::18 2001:db8:1:ffff::19 Pair #12 · …:18
13 2001:db8:1:ffff::1a/127 2001:db8:1:ffff::1a 2001:db8:1:ffff::1b Pair #13 · …:1a
14 2001:db8:1:ffff::1c/127 2001:db8:1:ffff::1c 2001:db8:1:ffff::1d Pair #14 · …:1c
15 2001:db8:1:ffff::1e/127 2001:db8:1:ffff::1e 2001:db8:1:ffff::1f Pair #15 · …:1e
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