Forging ipv6 addresses?

[Martin Lopreiato]

hello,

i want to send a packet with a forged ipv6 address. i tried using
sendmsg() with ancilliary data, but it seems I can only select an
address that has been configured on my system. if I select an
arbitrary ipv6 address that i want to forge, i get "can't assign
requested address" (in freebsd). isn't it possible to forge an ipv6 address
with sendmsg()?

note: if i use a configured address, my code works perfectly. so the
error message i'm getting when trying to forge an ipv6 address does
not seem to be related to a bug in my code.
thnx,
/m