DAD/tentative addresses vs system boot with network links down

Lutz Preßler Lutz.Pressler at SerNet.DE
Thu Mar 31 22:24:01 CEST 2011


On Thu, 24 Mar 2011, George Bonser wrote:
> > If one
> > - configures a static IPv6 address on some interface with normal
> >   (giving "ip address add ADDRESS dev DEV") config mechanisms
> > - uses this address in daemon configurations as "bind address"
> > - boots the system with link of DEV down
> > ... those daemons will fail to start.
> > 
> > The reason is, that an address is in state "tentative" until
> > duplicate address detection can be completed - which is
> > (per definition?) not possible on an unavailable link.
> > 
> Well, setting a sysctl for the interface might do it:
> /etc/sysctl.conf
> net.ipv6.conf.DEV.dad_transmits = 0
> So you basically turn off DAD for the interface.
Yes, thanks for reminding me of that option. But I don't think that disabling
DAD in general is a sensible way to handle this problem.
I'm a litte bit supprised that there are no other reactions here.
Don't you think this is a real operational problem for (Linux) server systems?
I do. And not only with normally unused interfaces, but there is also
the chance that after loss of power a (L3-)switch takes longer for starting
up than the server system...
I found out, that there is a Linux IPv4 socket option "IP_FREEBIND", but no
equivalent for IPv6.
Does anybody know how Windows Server is behaving?


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