Re: ipv6 / rtadv problem

On 29/03/2011, at 22:04, Bernd Walter wrote:
>> 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
> host.
> 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.

Thanks for the information.

> 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.

Hmm, I have pretty stupid hardware, I am fairly sure none of my switches understand multicast.

If I see it again I will try and get some more information

--
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
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