Cisco 7600 (7609) as a core BGP router.

Fri Jul 17 23:31:33 UTC 2009

> From: Brad Fleming <bdfleming at kanren.net>
> Date: Fri, 17 Jul 2009 18:07:26 -0500
> 
> We don't run very much Cisco gear (none of their larger, hardware  
> stuff) but I have a couple questions for the Cisco gurus out there...
> 
> According to this page:
> http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/product_data_sheet09186a0080159856_ps4835_Products_Data_Sheet.html
> The Cisco WS-SUP720-3BXL can hold "1,000,000 (IPv4); 500,000 (IPv6)"  
> route entries.
> 
> 1) Does that mean a) The card can hold 1m IPv4 routes --OR-- 500K IPv6  
> routes or b) 1m IPv4 routes --AND-- 500K IPv6 routes?

It means that it will hole 1M IPv4 OR 500K IPv6. It means that IPv6
addresses take twice the TCAM that IPv4 routes do, so that for every
IPv6 route in TCAM, you can load two fewer IPv4 routes.  Worse, TCAM is
partitioned with a dedicated portion for IPv4 addresses and another for
IPv6 + multicast. To adjust the partitioning, you must reload the
supervisor.

> 2) I'm assuming MPLS cuts into the number somewhere but could anyone  
> explain it briefly?

Not really. The TCAM holds routes and the place to send packets destined
for them. Since all TCAM is loaded based on flows and treated very much
like MPLS, just without an external tag, the TCAM space should not be
impacted. (I am NOT positive about this one, though.)

> 3) Do ACLs use some of these resources or do they get their own slice  
> of memory?

Nope. They are in a different TCAM in the Sup720. They have zero impact.

> That page also reports "up to 40 Gbps per slot of switching capacity;  
> 720 Gbps aggregate bandwidth".
> Is the 40Gbps per slot an aggregate or full-duplex value?

I don't entirely understand the phrasing of the question, but I think
you mean, do they double the numbers as router marketeers are wont to do
by counting traffic in both directions? 

No. That is why you can drive all 4 ports of the 4x10GE card to almost
the full 10G at the same time in both directions. Not quite, though.
Cisco "steals" a little bandwidth on each cord for some internal
signaling, so each pair of the 10GE ports is limited to about 19 GB. (I
don't recall the exact number.) So they are just slightly
oversubscribed.

The backplane is actually a pair of 20 Gbps backplanes with the ports
divided between them. On the 4x10G cards, the two top ports are on one
backplane and the two bottom ones are on the other. They each have
access to a full 20Gbps path less the "stolen" bandwidth.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
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