Re: [c-nsp] IOS XR filter route from OSPF?

On 11/28/23 17:02, Nick Hilliard via cisco-nsp wrote:

>
> prefix filtering is a defining feature of a policy routing protocol. 
> OSPF is a link-state protocol, and doesn't support the concept of 
> having different visibility of prefixes inside the same area.  If you 
> want that with OSPF, you'll need to divide your network into different 
> areas, which is messy. Probably better off using bgp for this.

Filtering in link state routing protocols is a bit of a misnomer, 
technically speaking... but, you can use import/export filters on 
routers with OSPF and IS-IS.

It would not necessarily limit the LSA/LSP flooding scope, but you end 
up with the desired outcome (all manner of caveats apply).

All that said, the usefulness of an IGP is in its homogeneous view of 
the network from and by all participating nodes. Bad things can happen 
when one partitions IGP's, especially in an unintended way. As you say, 
BGP is better for this kind of thing, as typically, IGP's should carry 
infrastructure prefixes, and you don't really want to filter those as 
they provide basic router-to-router connectivity.

Mark.
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