Re: force IPv6 SLAAC

[Anthony Fletcher <arif bifb org>]

Yes - you make a good point about the rules for the DUID. So I'm back to using different NM profiles or a script that sets a different static IPv6 address depending on the VLAN RA,

Anthony.

On Thu, 13 Feb 2020 at 12:26, Bjørn Mork via networkmanager-list <networkmanager-list gnome org> wrote:

Anthony Fletcher <arif bifb org> writes:

>> > My situation is with laptops in a large organisation with a central
>> > DHCP service. The DUID is static and so the laptop gets the same IPv6
>> > address even when it's moved to a different VLAN with a different
>> > prefix. When  I realise the IPv6 address is not appropriate I delete
>> > the lease file and then it all works until the laptop moves VLANs
>> > again.

This sounds like a severely misconfigured DHCP server.  If it serves
multiple network segments then it has to keep separate lease databases
for each network.

>> It sounds like you are in fact connecting to different networks
>> (VLANs). I guess, usually you would have different connection profiles
>> for each network.

The client shouldn't need to know anything about the network. Isn't that
the point of both DHCP and SLAAC?  Else it wouldn't be autoconfiguration...

> Could generating a fresh random DUID each time be a future option for a
> profile?

Yuck.  What point would the DUID serve then?

RFC3315 says

 "the DUID used by a client or server SHOULD NOT change over time if at
  all possible"

See https://tools.ietf.org/html/rfc3315#section-9

DUIDs should never change.  Expect all sorts of trouble if it ever does,
in all properly configured networks that is.

It sounds like you are dealing with a non-functional network. This
cannot be fixed at the client side. The best way to work around the
issues, if you only manage the client, is to configure static
addressing.


Bjørn
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