[ipv6-wg] IPv6 prefix delegation BCOP document available for comments and suggestions

Hi Jan,

It's not clear to me why in Section 3.1.5, a global /64 prefix is recommended
for PPPoE connections.

Sections 3.1.2 and 3.1.3 talk about directly connecting hosts without any
kind of CPE. As far I know, the last time that was in fashion for PPP links
was with dial-up. 

So I think that for PPPoE we can safely assume that a CPE can request a prefix
using DHCPv6 PD.

As indirectly mentioned in Section 3.1.2, assigning a global /64 to a
point-to-point link may open certain kinds of attacks. All links with a global
/64 risk a ND exhaustion attack. However, point-to-points also risk a ping-pong
attack.

For a PPPoE link these issues are trivially solved to leaving the link
unnumbered.