Obrigado pelos ótimos links, embora eu estivesse realmente atrás da resposta com relação ao significado dessas opções de IPv6 que eu especifiquei, e não links para o seu significado, já que os links podem sofrer de link-rot.
De:
IPV6ADDR #<addr/mask> - Where address is the first static, or primary, IPv6 address on an interface.
IPV6ADDR_SECONDARIES #<addr/mask> Option additional addresses .
IPV6_AUTOCONF #<yes/no> - Enable IPv6 autoconf configuration for this interface (an IPv6 address will be requested using Neighbor Discovery (ND)).
IPV6_AUTOTUNNEL #<yes/no> - Control IPv6 automatic tunneling (device sit0)
IPV6_DEFAULTGW #<addr> - IPv6 default gateway
IPV6_DEFROUTE #Does option even exist?
IPV6_FAILURE_FATAL #<yes/no> - Whether the device is disabled if IPv6 configuration fails.
IPV6FORWARDING #<yes/no>- Control IPv6 forwarding (box acting as router).
IPV6INIT #<yes/no> - Initialize this interface for IPv6 addressing.
IPV6_MTU #<integer> IPv6 MTU for this link.
IPV6_PEERDNS #<yes/no> - Does this option exist? I assume it does the same as the IPv6 version?
IPV6_ROUTER #<yes/no> - Control sending of router advertisements and isRouter on neigbor advertisements.
# defaults:
# IPV6_AUTOCONF=(see IPV6FORWARDING)
# IPV6_AUTOTUNNEL=no
# IPV6_FAILURE_FATAL=???
# IPV6FORWARDING=no
# if IPV6FORWARDING=yes: IPV6_AUTOCONF=no, IPV6_ROUTER=yes
# if IPV6FORWARDING=no: IPV6_AUTOCONF=yes
# IPV6INIT=no
# IPV6_PEERDNS=???
# IPV6_ROUTER=(see IPV6FORWARDING)
Fontes: link
e cat /etc/sysconfig/network-scripts/ifup-ipv6