Re: force IPv6 SLAAC

[Bjørn Mork <bjorn mork no>]

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