[j-nsp] preferring shorter prefixes

Richard A Steenbergen ras at e-gerbil.net
Fri Jul 14 17:29:46 EDT 2006

On Fri, Jul 14, 2006 at 04:13:14PM -0400, Chuck Anderson wrote:
> I want to basically say "all prefixes from AS A override those from AS 
> B".  I cannot know ahead of time which prefixes they are or what the 
> lengths are.  I would filter the longer/more specifics if I could 
> identify that there was a shorter/less specific prefix in the routing 
> table (there is no default route in the routing table in this case).

The only thing that trumps a more specific prefix is a different rib. 

We've probably all faced that same exact problem from a policy perspective 
at one point or another, and a diff rib is unfortunately the best answer. 
It's not theoretically impossible to do what you want (you could just have 
the software check for more/less specifics when doing best path seection 
before installing into the rib), but don't expect to ever see a vendor 
implement or support it. Also be careful not to exceed your dram/sram 
capacity when making extra tables, and if you need to do it a lot or on a 
large number of routes you are probably SOL.

Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

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