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List:       freebsd-net
Subject:    =?UTF-8?B?UTogW3J0YWR2ZF0gcHJlZml4IGluZm8gZmxhZyAnUicgLSBNb2JpbGU=?= =?UTF-8?B?IElQdjYgZXh0ZW5zaW9uI
From:       Harry Schmalzbauer <freebsd () omnilan ! de>
Date:       2017-11-24 19:55:28
Message-ID: 5A187930.1070406 () omnilan ! de
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 Hello,

it was unavoidable, so I took some time reading rtadvd.conf(5), rfc4861
(Neighbour Discovery for IP version 6, which also describes the Router
Advertisement Message Format with it's Prefix Information, flags L and
A) and rfc6275 (Mobility Support in IPv6, which extends the Prefix
Information Flags).

As far as I can tell, our rtadvd(8) doesn't support the extended 'R' flag.

My aim:
Stateful _only_ (dhcp6) configuration in the LAN for widest client
deversity possible, without the need to change anything on any client.

dhcp6 setup was no probelm with isc's dhcpd.
Finding the "managed adress" flag for RA messages, which tells most
popular clients to _also_ request DHCPv6 leases was also no big effort.
Finding the unwanted L flag for the prefix information in the RA message
was a bit trickier.
Finding out that rtadvd(8) seems to only respect the corresponding
"pinfoflags='l'" capability field if you explicitly set a addr for
prefix info (not leaving the auto-determination) was hard.

So for the records, if somebody else want's to restrict SLAAC in her
DHCPv6 environment, /etc/rtadvd.conf needs the following lines to
convince the most popular clients to use the stateful (dhcp6) address
for internet communication:
yourdefaults:\
        :noifprefix:nolladdr:raflags='m':
yourif:\
       
:tc=yourdefaults:addr="2001:db8:abcd:1::":prefixlen#64:pinfoflags='l':

(If you only set the 'm' flag, most popular clients use the SLAAC
address, despite they got a dhcp lease.)
In any case, they use the link-local address of the gateway.
I'd prefer that clients use the global unicast address of the router,
instead of the link-local address.

What I found so far is the already mentioned "R" flag, but that's not
implemented so far (in rtadvd(8)).

What do your setups look like?
Do you use radvd(8) instead?
Any other trick?
Not caring about source addresses at all?

Thanks,

-harry
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