OSPF generate default route

[Slawa Olhovchenkov]

On Mon, Aug 26, 2013 at 10:16:55AM +0200, Pavel Zichovsky - Internet Expert s.r.o. wrote:

> Hi,
> 
> > I have configuration problem: how I can generate default route in OSPF
> area?
> 
> Use static protocol with different bird table (and not connected to kernel
> table), add your route in it, an then using pipe transfer it into desired
> bird tables (to which other proocols - OSP,BGP are connected).

Why several bird table? What issues with one, common table?

> I am using this to insert some special routes (default outside and few
> specific internal routes) into OSPF and it works flawlessly.
> 
> > Generate, not redistribute from static kernel route or other routing
> protocol.
> 
> Using independent static protocol is de-facto "generate" :-) And if you use
> for it standalone config file, you can change it by external scripts and
> then run birdc configure to apply changed route.
> 
> > 
> > Generate, not installed into kernel routeng table.
> 
> If you use right export/import filter, then it won't change any kernel
> routing table.
> 
> > Next question: conditional advertise default route (for example -- if
> present
> > announce in BGP to some network).
> 
> Again, use export/import filters. They are very functional for almost
> everything you can imagine to filter :-)

I don't understand how in filter change (or add) network announce. In
documentation this attribute market as 'read-only'.