unnecessary and frequency kernel routing update

[Slawa Olhovchenkov]

On Wed, May 01, 2013 at 10:10:35PM +0200, Ondrej Zajicek wrote:

> On Mon, Apr 29, 2013 at 10:41:24PM +0400, Slawa Olhovchenkov wrote:
> > > If the received route update is exactly the same, then it should
> > > be ignored and not propagated further, but there is probably some
> > > minor change (like in BGP attributes) that forces the propagation.
> > 
> > How I can see in debug log whats chnged?
> 
> There is no easy way, either you could put print commands to
> import/export filters for specific route attributes (like bgp_path), 
> or you coud try to catch it interactively by 'show route all'.
> 
> > > BIRD currently does not support anything that could prevent propagation
> > > of frequent updates.
> > 
> > I thinks this is useful feature.
> 
> Yes, but problematic to implement in the current design.

Why? protocol kernel know about current route. If this route don't
changed (same next hop, weight if support, etc) -- don't propagate
this update to kernel.

> > > For the kernel protocol it could be hacked by removing the code that
> > > handles route updates and depending just on periodic routing table scans
> > > for BIRD-kernel routing table synchronization.
> > 
> > This is bad point. For external BGP update this semi-reasonably, but
> > for OSPF/etc this is unacceptable.
> 
> Well, for OSPF such problem cannot happen, as OSPF recalculates routes
> at most once per second.

uhhh. What about support OSPF sub-second timers?

> But it is true that it is a hack.

kenel routing update collected from OSPF and BGP together.