[f-nsp] NetIron MLX Experience..

[Richard A Steenbergen]

On Wed, Aug 09, 2006 at 12:23:55PM +0200, Gunther Stammwitz 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.  
> 
> Correct, this is what net-aggregate does and why one can still run the old
> ironcore-based bigirons/netirons with full routes these days.

Sortof, but I wouldn't call net-agg a FIB really. Net-aggregate is a CAM 
aggregation tool which lets you install less routes into the CAM if you 
have a default route. The difference between net-agg and dr-agg is that 
dr-agg aggregates you down to a single 0.0.0.0/0 CAM entry and only 
installs entries for routes which don't point to whereever your default is 
going, while net-agg installs the default as 4096 /12s (so you have some 
vague hope of load balancing properly if you have multi-path defaults). Of 
course this DEPENDS on a default route to work, so you wouldn't want to 
run these in a default free core obviously. The next kick in the teeth for 
cam exhaustion used to be how they handled local arp based routes. If you 
have ip address 1.2.3.1/16 nailed up to an interface, and a worm came 
through and scanned every IP on that /16, your box would try to burn 64k 
cam entries. :)

Original Ironcore boxes only had capacity for 8k 16k or 32k cam entries 
depending on model, so you really needed aggregation like this to handle 
random destination or "internet core" traffic. The modern boxes have more 
than enough tcam to handle full routes of course.

-- 
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)