I ran # update; locate Configure.help # Nothing. web-search only finds: ./configure --help (WRONG thing)

From http://www.slackware.com/releasenotes/packages15.0.php

PACKAGE NAME: iproute2-5.16.0-x86_64-1.txz
PACKAGE LOCATION: ./slackware64/n
PACKAGE SIZE (compressed): 968 K
PACKAGE SIZE (uncompressed): 3270 K
PACKAGE DESCRIPTION:
iproute2: iproute2 (IP routing utilities)
iproute2:
iproute2: These are tools used to administer many advanced IP routing features
iproute2: in the kernel. See Configure.help in the kernel documentation
iproute2: (search for iproute2) for more information on which kernel options
iproute2: these tools are used with.
iproute2:
iproute2: These utilities were written by Alexey Kuznetsov. The current
iproute2: maintainer of iproute2 is Stephen Hemminger.
iproute2:

It looks like that's been gone since linux-2.6. Thanks for the notice.