net.inet6.icmp6.nd6_useloopback - what is it supposed to do?

[Hiroki Sato]

Garrett Cooper <yanegomi at gmail.com> wrote
  in <CAGH67wQWu2PZGcORsiSz3_r+mjsDv=Fx9-ijbEJQv8jbt7a7bg at mail.gmail.com>:

ya> Hi,
ya>     I've been TAHI testing FreeBSD 7.x sources for the past couple
ya> months and over the course of my testing via the TAHI IPv6 conformance
ya> test, I changed the knob value from net.inet6.icmp6.nd6_useloopback=1
ya> -> net.inet6.icmp6.nd6_useloopback=0 and ran into a slew of errors
ya> with the addr.p2 phase-1 TAHI tests.
ya>     I was wondering if someone could describe what the beforementioned
ya> sysctl is supposed to do from a functional perspective, how it might
ya> tie into other IPv6 RFCs (if applicable), and if disabled how it would
ya> affect a system with IPv6 enabled.

 It is for whether a loopback address (::1) is used as the destination
 for traffic toward one of the locally-configured IPv6 addresses.  In
 the original implementation it is in rtrequest(), but the current
 FreeBSD's one it just means if a loopback route will be installed or
 not upon the lo0 interface initialization, not in RTM_RESOLVE.  So,
 if setting nd6_useloopback to 0, no loopback route will be installed
 and some THAI test will fail, I think.

-- Hiroki
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