On Jun 12, 2009, at 8:42 AM, Kevin Loch wrote:
Łukasz has already addressed this; suffice to say he's right, and
the above is not correct. A TCAM lookup *is* the forwarding
operation, and the DFC has all information required locally to
switch the packet (via the fabric) to the output linecard, and does
so.
I shouldn't have said PFC. The fabric is on the supervisor card itself
not the PFC. What I meant was the packet is always sent to the
centralized switch fabric on the active supervisor card regardless of
where the lookups/acl are done.
Just for information, I know very intimately how this stuff works and
don't need you to explain it to me. I haven't objected yet because
others might find this interesting. (and FYI, your last sentence is
wrong too if DFCs exist on each card)
The important point is that the lookup limitations (mpps) are
different than the fabric bandwidth limitations (gbps) because of how
these functions are separated on the cef720/dcef720 platform.
A 6509 should not "fall over without DFC's" unless you are doing more
than 30mpps. That is 15gbit/s of 64 byte packets or 360gbit/s of
1500 byte packets.
Sorry, let me back up and explain again. I've been dealing with Cisco
for 20 years now. And I very well know Cisco's ability to super-
inflate their packet handling ability. And specifically, I have run
6509 systems into the ground with a mere 500mb/sec of traffic.
Their whole MPPS statistics are based on perfect-world scenarios that
don't exist. And honestly, I have on 5 different occasions had the
opportunity to push Cisco to prove those numbers, and they have failed
to do so IN A LAB THEY DESIGNED JUST TO DO SO.
So ... yeah. Don't go believing those statistics.
Now let's talk about reality: 1/10 inbound/outbound ratios, 5% of
received traffic is Internet cruft requiring (wasted) TCAM lookups,
etc and such forth than any provider peering router observes, and
you're down to a much lower ratio. Fail to install DFCs and you'll
find your 6509s falling over with just a few gigabits of traffic.
30mpps versus 48mpps gives an illusion that DFCs only give you another
50%, but that's not reality on the ground. Don't try and persuade me
otherwise, I've seen this repeatedly in real life environments.
Now, let's stop talking about non-DFC cards and start talking about
equipment which can handle uRPF on every port, full Netflow analysis
of up to 8 ports at a time, every port layer 3, every port filtered,
colo facility core/peering.
--
Jo Rhett
Net Consonance : consonant endings by net philanthropy, open source
and other randomness
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