IPv6 router advertisement

[Mihai Moldovan]

Sorry for not responding so long, I've been putting v6 aside for a while
because of compilation and configuration problems and thought it might
be cool to get it finally working, until...


* On 20.04.2009 19:37, David W. Hankins wrote:
> On Sun, Apr 19, 2009 at 09:38:54AM +0200, Mihai Moldovan wrote:
>   
>> radvd is due to the small subnet size not working of course, so not
>> employable.
>>     
>
> I thought radvd can announce the prefix with the SLAAC bit cleared?
>
> The currently (deployed) IPv6 model is that you MUST have an RA that
> delivers the default router and locally attached prefix information.
>
> So working out how to get radvd to emit what you want is the key.
>   

Currently, my radvd is set up this way: (information acquired by
radvdump on one machine which is of course not the server/router itself)

#
# radvd configuration generated by radvdump 1.1
# based on Router Advertisement from fe80::21b:21ff:fe2a:c4fe
# received by interface eth0
#

interface eth0
{
    AdvSendAdvert on;
    # Note: {Min,Max}RtrAdvInterval cannot be obtained with radvdump
    AdvManagedFlag off;
    AdvOtherConfigFlag off;
    AdvReachableTime 0;
    AdvRetransTimer 0;
    AdvCurHopLimit 64;
    AdvDefaultLifetime 30;
    AdvHomeAgentFlag off;
    AdvDefaultPreference low;
    AdvSourceLLAddress on;

    prefix 2001:41d0:1:678e:abcd::/96
    {
        AdvValidLifetime 2592000;
        AdvPreferredLifetime 604800;
        AdvOnLink on;
        AdvAutonomous on;
        AdvRouterAddr off;
    }; # End of prefix definition

}; # End of interface definition


Also, the DHCP server is set up to give out one fixed address out of
this very /96 pool. (ISC DHCPd of course! :))

subnet6 2001:41D0:1:678E:ABCD::/96 {
  default-lease-time        3600;
  max-lease-time        21600;
}

  host sui-wlan {
    host-identifier option dhcp6.client-id
00:01:00:01:4a:00:49:71:01:72:e6:b7:6c:21; # < seems like
https://fedorahosted.org/dhcpv6/ is generating some other DUID than ISC
dhclient-4?! > 00:01:00:01:11:92:FB:91:00:90:F5:48:96:D0; # default MAC
> 00:90:F5:48:96:D0;
    fixed-address6 2001:41D0:1:678E:ABCD::2;
  }

Now to come to some terms...

> Note however that at least dhclient, and one or two others, DHCPv6
> software will presume a /64 prefix for any offered addresses, in order
> to work around a bug-in-the-protocol where an RA failure leads to the
> addressed clients being unable to speak to each other.
>   
Exactly this is what is happening. I've tried all to me known DHCPv6
clients, that is ISC dhclient and dhcpv6 (see URL above) - dhcpcd yet
has no v6 support, though it is to be included soon according the
project owner.

This behavior is of course causing a lot of trouble around - although
the address is given out correctly, other hosts in the same /64 subnet
cannot be accessed, but you already now this. :)

Another problem is that RA totally refused to work. Although I can see
advertisements via radvdump, nothing happens automagically. I don't know
how to track this, I even have got absolutely no evidence of ra in my
kernel log ring buffer output (Linux 2.6.28.7 for instance), that is, in
dmesg.

I have even tried removing all IPv6 addresses and routes and adding the
IP manually via ip -6 addr a 2001... dev eth0 and waiting some minutes
to see if ra is working then, but nothing happened. The only way seems
to be adding the route by hand which... sucks.

> There's currently a default gateway and prefix option draft before the
> DHC WG, which will help us resolve the above bug-in-the-protocol and
> eliminate the strict requirement for RA
I've stumpled upon an RFC implementing the routers option in DHCPv6, but
can't remember the URL anymore - is this the thing you refer to? :)

It would be perfectly cool to have a working setup which is independant
from autoconfig - either my current one is wrong (both dhcp and ra wise)
or I'm doing some things completely wrong.

Best regards,


Mihai Moldovan

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