[Dibbler] Mixed stateless autoconfiguration and DHCP

Tomasz Mrugalski thomson at klub.com.pl
Fri Jun 27 00:31:18 CEST 2008


On Fri, 27 Jun 2008 somebody known as Karl Auer wrote:

> After many months away, I'm returning for another of CMOT's buns.
>
> I'm trying to set up a subnet where stateless autoconfiguration and
> DHCPv6 are mixed.
>
> The difficulty I have is that even if I set the "dynamic" flag on the
> client's interface to off, the interface still sets up an address via
> stateless autoconfiguration as soon as a router starts advertising.
>
> The dynamic flag does seem to be used and understood in other ways. If I
> set it on, a "DYNAMIC" attribute appears on the interface. That
> attribute disappears if I turn the flag off. Also, flushing dynamic
> addresses discards the address obtained via stateless autoconfiguration.
> Have I misunderstood the purpose of the "dynamic" flag?
I have not used dynamic flag, but it seems to be for something else.
According to ifconfig manpage:

dynamic
               Mark  the interface as having dynamic IP addresses.
               When the interface goes down or an associated  isdn
               device  hangs  up all TCP sockets having its source
               address are reset.

To disable, stateless autoconf, you have 2 options:
1. reconfigure your router to disable autonomous bit in its adverisements.
With this bit disabled, hosts may still configure routing, but are not 
allowed to generate their addresses. If your router happens to be 
Linux/unix box running radvd, add "AdvAutonomous off" to its 
/etc/radvd.conf.

2. Ignore RAs on your host. To do so, use this command:
echo 0 > /proc/sys/net/ipv6/conf/eth0/autoconf

You may also want to inspect /proc/sys/net/ipv6/conf/eth1/ directory, as 
there are other kernel parameters that may be tampered with.

> Any ideas? How can I stop an interface obtaining an address via
Just those two. If they don't help, let me know. I'll figure something 
out.

Just a small note to other people, who may be interested. That has nothing 
to do with dibbler and DHCPv6. Those flags are for stateless autoconf 
only.

There's separate bit in RA message that instructs host to use (or not) 
stateful autoconf, i.e. DHCPv6, but it is shamelessly ignored by 
dibbler :).

Cheers,
Tomek



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