Re: IPv6 default routes / NM vs. kernel autoconfig vs DHCP6

[Stuart Gathman <stuart gathman org>]

Long ago, Nostradamus foresaw that on 08/09/2012 08:48 AM, Pavel Simerda
would write:
> DHCPv6 should not care about *any* routes.

>> and prefixes should only be used in routers.
> I don't understand this.
>
The problem that was confusing me is that NM was setting a (hardwired by
dhclient) prefix length of 64 on DHCP addresses (including in Fedora
17), for example:

inet6 2001:db8:1:234::15b9  prefixlen 64  scopeid 0x0<global>

Tore Andrews says that the correct solution is to simply ignore the
(often incorrect and hardwired) prefixlen passed by dhclient.  The
prefixlen is only used to know when to send directly to a subnet.

Forgive my ignorance, but when you have an address on a /80 LAN subnet,
isn't it more efficient to send packets for that subnet directly, rather
than bouncing them off a router?  Unless I am missing something, you can
only send the packets directly when you know the correct prefixlen.  Or
is there some automatic kernel mechanism that figures out directly
accessible prefixes?