And from /usr/share/doc/initscripts-9.49.37/sysconfig.txt
IPV6ADDR=<IPv6 address>[/<prefix length>]
Specify a primary static IPv6 address here
Optional, if normal host and a router advertisement daemon is on local link
Required, if node is a router and interface should route packets
Note: if prefix length is omitted, 64 is assumed
And from /usr/share/ doc/initscripts -9.49.37/ sysconfig. txt
IPV6ADDR=<IPv6 address>[/<prefix length>]
Specify a primary static IPv6 address here
Optional, if normal host and a router advertisement daemon is on local link
Required, if node is a router and interface should route packets
Note: if prefix length is omitted, 64 is assumed