[Lloyd Parkes]
[...] now I'm getting packets, but they're addressed to a multicast
address, ff02:3::1:ff02:2, not the address userland is sending to.
That might just be your system trying to find its default route.
Possibly, but I wouldn't expect it to be. I configured tun9
inet6 fd1e:5a23:d977:3681::2:1 prefixlen 112
(the host has no other non-link-local v6 addresses) and ping6ed
fd1e:5a23:d977:3681::2:2. (There's nobody there, because the peer
isn't set up at the moment, but the v6 stack has no way of telling
that.) Thus, the target should be on-net and it should be doing ND
rather than rtsol.
If that's the case, then requests to ff02:3::1:ff02:2 could well be
the kernel trying to find all local routers.
What does tcpdump say is inside the ND request?
If that's what it is.
Oh, this is interesting.
tcpdump says
17:52:02.019960 IP6 fd1e:5a23:d977:3681::2:1 > ff02::1:ff02:2: ICMP6, neighbor solicitation, who has fd1e:5a23:d977:3681::2:2, length 24
(repeated a handful of times). But the destination address I'm seeing
is ff02:3::1:ff02:2. This then leads into....
[Michael van Elst]
that, and now I'm getting packets, but they're addressed to a
multicast address, ff02:3::1:ff02:2, not the address userland is
sending to.
I would guess that's an embedded scope (and must not appear on the wire).
sin6->sin6_addr.s6_addr16[1] = htons(zoneid & 0xffff);
where zoneid for a link-local address like ff02:: (or an
interface-local address) is the interface index.
Curious. My code is printing the address prepended by tun, not the
destination address in the packet; looking at if_tun.c (which I _have_
modified), this is the address in the third argument to tun's if_output
(const struct sockaddr *dst). What, if anything, is the v6 stack
expecting the network interface to do with this address?
But ff02::1:ff02:2 would be a solicited-node multicast address for
something with an anycast or unicast address of anything:XX02:0002.
That probably is where that address came from, then: the solicited-node
address for the target.
When the 4291 says that a node is required to (compute and) "join (on
the appropriate interface) the associated Solicited-Node multicast
addresses for all unicast and anycast addresses that have been
configured for the node's interfaces", is that anything that would lead
to a downcall to the relevant driver (tun, in this case), either to
send traffic or for any more host-internal purpose?