On Thu, Dec 04, 2003 at 10:27:54AM +0100, Michael Bussmann wrote:
> However, I still notice an oddity: MLD packets are not recognised as
> icmpv6 messages.
That's bad. Are you talking about MLDv1 or MLDv2 packets?
> I set up a simple set of rules that directs both icmpv6 packets and "any"
> packets (just for testing purposes) to the QUEUE target. An application
> program (using libipq) dumps all packets:
Ouch. We have two issues here:
1) ip6_tables not matching it as icmp6 packet
This basically means that skb->nh.ipv6h is not initialized, or
points to skb->raw instead of the ipv6 header.
I cannot see how this could happen in the mld_sendpack(), since
itself dereferences skb->nh.ipv6h
In the igmp6_send() case, ip6_nd_hdr() initializes skb->nh correct,
so I also cannot see this happen.
2) ip6_queue copying the linklayer header to userspace
This means that skb->data does not point at the beginning of the
ipv6 packet (i.e. skb->data != skb->nh.ip6h), but to the beginning of
the hardware header (i.e. skb->data == skb->head).
This is because mcast.c writes the full packet including the hardware
header and _then_ calls NF_HOOK. All other code (ipv6 or ipv4) is
building the layer 3 packet, then calling NF_HOOK and later on (via
ipX_outpur_finish() or dst_output()) adding the hardware header.
> I'm not sure whether this is a bug, but it seems to be inconsistent that
> some icmpv6 packets are dumped with the LL and others are not.
of course it is a bug.
So the fundamental question (with regard to the ipv6 gods) is: Is it
really necessarry that the ipv6 mcast code bypasses the destination
cache?
IPv4 multicast just uses the dst_cache, and thus sends the packet using
the normal dst_output() functions.
I have to admit that I'm not as fluent with the code to decide why ipv6
multicast is the only code in ipv4/ipv6 that manually adds the hardware
header and bypasses the normal dst_otput() way?. Can somebody explain?
> Let me know if you need further information.
As I am currently travelling, I cannot really play with any multicast
networking (just a single notebook machine here, and it is ppc, so no
user-mode-linux).
> Best regards,
> MB
--
- Harald Welte <laforge@xxxxxxxxxxxxx> http://www.netfilter.org/
============================================================================
"Fragmentation is like classful addressing -- an interesting early
architectural error that shows how much experimentation was going
on while IP was being designed." -- Paul Vixie
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