[Babel-users] AHCP and yo-yo interfaces [was: Babel for use in a dense...]

[Gabriel Kerneis]

On Mon, Jul 01, 2013 at 11:56:50AM +0200, Baptiste Jonglez wrote:
> On Sun, Jun 30, 2013 at 09:01:30PM +0200, Juliusz Chroboczek wrote:
> > If you want to try your hand at fixing it, it's check_network in
> > ahcpd.c.  Note that the natural solution is racy (an interface could
> > go down-up before ahcpd notices), and the right solution is quite
> > a bit of work (it would require monitoring interfaces through netlink,
> > yuck).
> 
> While we're at it, I believe there are a number of ways to improve
> ahcpd

Well, while we're dreaming of ahcpd as a really poweful tool, we could also
implement RFC 4941.  It probably wouldn't even be that hard if we implemented
netlink monitoring first: install addresses with finite values for valid_lft and
preferred_lft, let the kernel deal with the timeouts, and allocate new addresses
when they expire (which you have to do anyway if the address disappears for any
reason, such as a yoyo-interface).

(Of course, this is slightly incorrect: you should ideally reuse the address if
the interface goes down/up instead of choosing a new one, but it would mean
duplicating the timeout mechanism in user-space which seems a bit silly.)

-- 
Gabriel