direct routes and SLAAC addresses

[Ondrej Zajicek]

On Thu, Jul 08, 2021 at 10:56:18AM +0100, George Ross wrote:
> Many thanks for answering my stubnet question a couple of weeks or so back. 
> I have a supplementary direct-protocol question now...
> 
> We have a Linux router running BIRD 2.0.8.  It has some interfaces on which 
> we configure IPv6 addresses statically.  We turn off auto-configuration, 
> but, due to a race condition which it's going to be hard to fix, when we 
> reboot the machine we can end up with SLAAC addresses as well as the static 
> IPv6 addresses.
> 
> We start BIRD, and the direct protocol imports the subnets, so we can then 
> export them to BGP.  The problem seems to come when the kernel ages out the 
> SLAAC addresses.  It looks as though when a SLAAC address goes, the 
> direct protocol notices and stops importing the corresponding subnet.
> Unfortunately, it looks as though it doesn't realise that there's still a 
> static IPv6 address for the subnet, and that it should therefore continue 
> to import it.

Hi

That is probably an issue with the Direct protocol and IPv6. In IPv4,
there is only one 'primary' address per IP range and iface, others are
marked 'secondary' by the kernel, so we just ignore secondary ones and
add/remove prefix when primary address is added/removed. But seems that
in IPv6, this is not the case and there is no secondary flag.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."