Cisco 7600 (7609) as a core BGP router.

Richard A Steenbergen ras at
Fri Jul 17 18:37:34 CDT 2009

On Fri, Jul 17, 2009 at 06:07:26PM -0500, Brad Fleming wrote:
> 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?

Woops, I missed this question. On CEF720 (aka the cards numbered 67xx
that claim to be 40G/slot) what you actually have are two 20G fabric
channels to each slot. The fabric channels are full duplex, so you could
have 40G per slot coming in and out of the same card, and Cisco
double-counts the packets (in and out) to get 9 fabric slots * 40G * 2 =

On 6704 cards, ports 1 and 2 are in one fabric channel, ports 3 and 4
are in another. On 6748 cards, even ports are in one channel and odd
ports are in another. On 6724 cards, there is only one 20G fabric
channel. Of course there are literally a list of caveats a mile long to
explain why you won't actually get anywhere near 720G out of the box,
but the big one you want to be careful of is sending traffic within the
same fabric channel (i.e. from port 1 to port 2 on a 6704). This will
cause a bottleneck at around 7-8G, with lots of input or output drops. 
You can also view the fabric utilization with "show platform hardware 
capacity fabric", though you should keep in mind that these counters are 
about as accurate as the others on this platform (wild variations at 

Richard A Steenbergen <ras at>
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

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