Marc Lehmann pointed out that binary prefixes are made up by the IEEE and

are not official SI yet. (Debian Bug #182478)

man/en_US/ifconfig.8

@@ -192,7 +192,7 @@ rules for the address using the
 .BR ipchains(8)
 command.
 .LP
-Since net-tools 1.61 ifconfig is printing byte counters with SI units. So
+Since net-tools 1.61 ifconfig is printing byte counters with IEC 60027-2 units. So
 1 KiB are 2^10 byte. Note, the numbers are truncated to one decimal (which can
 by quite a large error if you consider 0.1 PiB is 112.589.990.684.262
 bytes :)