[f-nsp] NetIron MLX Experience..

[Richard A Steenbergen]

On Tue, Aug 08, 2006 at 03:26:56PM -0700, Joseph Jackson wrote:
> 
> Foundry does NOT store the full routing table in the FIB it only stores
> the most specific.  The way I understand it, (as explained to me by a
> foundry SE).  Is that any changes to the RIB get populated to the FIB
> only if a more specific route is found.  

Uh right, thats why it is called a FORWARDING information base. Only the 
data that is used for forwarding is installed in the FIB, but the point is 
that it is pre-populated with forwarding data for the entire table rather 
than a "cache" which is only populated on demand. If there is a less 
specific route which changes but it is covered by more specific routes 
which do not change, nothing in the forwarding table changes. The same 
holds true for routes which are not selected as best path.

The problem with historic non-prepopulated lookup methods is that the 
first lookup to a destination which has never been encountered before must 
take the "slow path" through the CPU, resulting in non-deterministic 
performance, and Very Bad Things (tm) when random destination traffic 
(think worms scanning the Internet for new victims) hits your network. By 
prepopulating the FIB, get consistent lookup performance to any 
destination.

-- 
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)