For no significant reason I decided to disable ipv6 on all local Slackware systems. Well, perhaps one reason. There is no need for ipv6 on the home LAN.
The process went quickly with only a few files to edit.
alias net-pf-10 off # INET6, IPv6 Protocol alias ipv6 off
Comment out the following two lines:
#udp6 tpi_clts v inet6 udp - - #tcp6 tpi_cots_ord v inet6 tcp - -
Possibly some of the edits were not needed but I did not test.