IPv6 router advertisement

Mihai Moldovan ionic at ionic.de
Wed May 6 14:00:41 UTC 2009

* On 05.05.2009 22:09, Ted Lemon wrote:
> On May 5, 2009, at 2:58 PM, Paul Selkirk wrote:
>> I've confirmed the RA behavior. radvd is perfectly happy to advertise
>> a /96 prefix with the A bit set, but the client won't auto-configure
>> an address. RFC 4862 doesn't put a limit on the prefix length, but
>> dmesg reports "IPv6 autoconf: prefix with wrong length 96" (Linux
>> kernel Do you feel like hacking the kernel?
Here lies another problem, my Kernel does not say *anything* which is
weird in itself already.
There *none* message about IPv6 in dmesg but the normal "eth0: no IPv6
routers present" on bootup message. Other than that, nothing.

> So Linux is doing the right thing here.
I'd like to disagree here. :-)
Windows can handle it very well obviously. I just added an address via
ipv6 adu 4/2001:41d0:1:678e:abcd::3 and Windows XP was able to get his
route automagically via ra.

> If you want to use a /96, you have to either use stateful address
> configuration (DHCPv6) or manual configuration.
Well, currently that's the plan, really! I'd like to use DHCPv6, but
this is only working for giving out addresses. For routing purposes, I
wanted to use ra (pure RA without autoconfig/address autoconfiguration.)
Once again, this has some backsides which are protocol-driven: all
DHCPv6 clients will assume a netmask of 64, thus making all machines on
my /64 subnet unreachable but in my /96 subnet (which is the LAN anyways.)

So the question in charge basically is why RA does not work on my
Laptop, but on Windows XP. I've thought of wrong settings in sysctl, but
everything is fine, and disabling RA kernel-wise using any options seems
not to be possible either, so it doesn't seem to be a configuration problem.

Maybe is just faulty at some point though.

I will fire up some Debian host here and look whether Debian's Kernel
experiences the same problems or not.

Other than that I am out of ideas and it seems like I'd have to wait for
the "routers" and "subnet" options being implemented in ISC DCHP and as
well interpreted via dhclient.

Best regards,


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