commit: 7e1203f36d86742147600cd7fbca141a07df32e4
parent f274e82ad0c8f000d8a65a9a96faa779a510edf5
Author: Haelwenn (lanodan) Monnier <contact@hacktivis.me>
Date: Sat, 18 Oct 2025 15:52:56 +0200
cidr2list.1: Add rationale on IPv6
Diffstat:
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/cidr2list.1 b/cidr2list.1
@@ -6,12 +6,12 @@
.Os
.Sh NAME
.Nm cidr2list
-.Nd expand cidr ranges into a list
+.Nd expand CIDR ranges into a list
.Sh SYNOPSIS
.Nm
.Sh DESCRIPTION
.Nm
-reads cidr ranges and cidr-less IPv4 addresses from standard
+reads CIDR ranges and CIDR-less IPv4 addresses from standard
input and prints the full list of the addresses of their range,
assuming a /32 for CIDR-less addresses.
.Sh EXIT STATUS
@@ -24,5 +24,16 @@ $ printf '%s\en' 192.168.0.42/31 192.168.0.69/31 | cidr2list
192.168.0.68
192.168.0.69
.Ed
+.Sh RATIONALES
+.Nm
+doesn't supports IPv6 because the typical usage would be extremely
+large ranges like /48 and /64 which would respectively imply
+printing 2^(128-48) and 2^(128-64) IPv6 addresses.
+Which cannot fit into current (2025) storage, let alone RAM.
+.Pp
+Meanwhile even printing 0.0.0.0/0 (all of IPv4) would take less than
+(2^32)*16\ =\ 64\ GiB, which is big but not impractical.
+.br
+16 being the maximum used for each line: 4*3 digits, 3 dots, 1 newline.
.Sh AUTHORS
.An Haelwenn (lanodan) Monnier Aq Mt contact@hacktivis.me
