[c-nsp] When to switch to DFC3BXL

[Richard A Steenbergen]

On Fri, May 18, 2007 at 03:47:07PM -0700, bill fumerola wrote:
> On Thu, May 17, 2007 at 10:49:40AM -0500, Janet Plato wrote:
> > On 5/16/07, Chris Woodfield <rekoil at semihuman.com> wrote:
> > > "show platform hardware capacity" gives you some pretty good data
> > > that may be useful in this situation. I think SXD was the first minor
> > > rev to support it, but I could be wrong.
> > >
> > > -C
> > 
> > Thanks for the info.
> > 
> > FWIW, I've got it in 12.2(18)SXF4 but not 12.2(18)SXE5.
> 
> data point: i don't have it in 12.2(18)SXE6a

This is not exactly mysterious stuff. :) Show platform hardware capacity 
was added in SXF, and is mostly composed of other data that you can access 
in various ways other under commands in a less user friendly form.

A PFC is limited entirely by the classic bus, since packet lookups on a 
non-DFC card must be sent to/from the PFC over it. The classic bus is 
32Gbps (thats marketing for 16Gbps full duplex), and when it runs out, you 
are done. The amount of capacity consumed on the classic bus depends on 
the forwarding mode of the box, and the type of packet. If you have all 
fabric-enabled cards (65xx+) you consume 32 bytes/lookup (compact mode) 
for v4 and get 30Mpps out of that 16Gbps. If you have any classic 
non-fabric cards (61xx - 64xx) in the chassis, the entire chassis falls 
back to truncated mode (64 bytes/lookup) and you get 15Mpps for v4. IPv6 
and MPLS consumes 33% more, so if you sent all v6/mpls you would get 
20Mpps and 10Mpps for compact and truncated mode respectively.

Of course actual traffic patterns are probably not all of one type or the 
other, but the good part is you can monitor this with "show catalyst6000 
traffic-meter" (if you have a sup720 3b/3bxl but not 3a, and upgrading the 
pfc doesn't count this feature is tied to the actual sup). Any packet data 
you send over the classic bus will of course deduct from this, so if you 
have a chassis doing 16Gbps on the classic bus you will have 0 pps 
available for PFC lookups. The only other caveats are a) recirculation can 
be caused by various things and count as a double hit, and b) if you send 
the entire packet over the classic bus you don't need to send the 64 byte 
lookup over it, since it's already on there. :)

-- 
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)