why use prefixlen 128 on Mac while IPv6 Address from HE has prefixlen 64?

[sleepingdust]

This might be a complete amateur question:

My IPv6 address assigned by HE is something like 2001:470:20:5c2::2/64

If I understand this correctly, the number after the oblique (/) is the prefix length, then why the tunnel tutorial Configuring a tunnel under *BSD & MacOS X uses prefix length 128 for Mac?

Should it be:
ifconfig gif0 inet6 $ipv6b $ipv6a prefixlen /64
instead of
ifconfig gif0 inet6 $ipv6b $ipv6a prefixlen /128

Thanks!

[cholzhauer]

IIRC that was a change in newer versions of OSx (someone please correct me if I'm wrong) and the tutorial was obviously written before the new versions were released.

[sleepingdust]

But why ifconfig gif0 still show the prefixlen 128 when I configured it with prefixlen 64?

Code Select Expand

gif0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1280
tunnel inet 192.168.1.141 --> 216.218.221.6
inet6 fe80::21b:XXXX:fe93:eee%gif0 prefixlen 64 scopeid 0x2
inet6 2001:470:18:XXX::2 --> 2001:470:18:XXX::1 prefixlen 128