ipv6 / rtadv problem
ticso at cicely7.cicely.de
Tue Mar 29 12:07:40 UTC 2011
On Tue, Mar 29, 2011 at 08:24:53PM +1030, Daniel O'Connor wrote:
> On 29/03/2011, at 19:05, Sergey Kandaurov wrote:
> >> This is repeatable after a reboot, I haven't experienced with FreeBSD 8.x.
> > I would assume an NDP communication problem or some such,
> > it would be interesting to see this sort of traffic, also ifconfig and
> > ndp -a output.
> Grr.. I had to reinstall today because I forgot to create a swap partition and now I can't reproduce the problem :(
NDP effectively replaces ARP for IPv6.
Like ARP it is also learning by received packets and not only by direct
query and because of this problems might be unnoticed.
Unlike ARP NDP is using multicast - instead of sending the inquiry to
a broadcast address each address has a solicatated multicast address where
the query goes to.
A NIC driver might have broken multicast support, I doub't that's a
problem for your em, but it is more likely that the bug is on the other
It also could be a problem with multicast aware switches - getting
multicast switiching right isn't an easy task and many implementations
are full of bugs.
If an NDP entry expires a host typically reasks using the unicast address
and the last known MAC, so once everything seems to run an underlying
multicast problem can live unnoticed for a much longer time.
Currently my own LAN router has a NIC driver with broken multicast
support and nevertheless everything seems to work fine since months
now, but I know the bug is there and that it can bite me each day.
And unlike ARP NDP is ICMPv6 and not an individual protocol, some
people agressivlely filter ICMPv*, which can easily catch too much.
Especially since many people configuring filter lists are not aware
of those solicitated addresses.
My assumption is that the problem is with the other host or switch
network and you just never noticed this so far because this kind of
problem can easily hide for a very long time.
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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