[c-nsp] Nexus 5596 architecture

John Gill johgill at cisco.com
Mon Jan 30 18:52:23 EST 2012

Hi Jiri,
This sounds pretty straightfoward, the thing you need to look at most 
closely now is the traffic flows.  Being all 10G is good because you 
will be cut-through switching unless there is congestion, which causes 
you to queue (store and forward).

Do you expect multiple ports to be talking to one port at the same time? 
  If this is the case, your decision will need to include how much 
buffering you require to be able to handle this congestion.

The common misunderstandings I see on this platform vs some other 
switches are the concept of cut-through switching and ingress queuing. 
Cut-through switching results in errors not being detected until after a 
frame is transmitted, so we may see one initial error increment errors 
across multiple switch hops - the advantage is low latency and low 
jitter.  With ingress queuing, you have to look for queuing discards on 
the input port so knowing your traffic patterns is very helpful for 
understanding where congestion could occur.  The switch spreads 
congestion out amongst all input ports so every port contributing to the 
congestion is responsible to handle it's own queue.  To be clear, the 
fabric is non-blocking, but you can always have scenarios where you have 
2+ ports sending to 1 port.  This can happen for a short time, but not 
indefinitely without queue drops.

This 5548P architecture document certainly applies for the 5596UP, 
except we have more ports and a scaled up fabric.  The "U" designates 
the ports are Universal, meaning they can be configured for ethernet or 


Obviously I am telling you what cisco has already available, but I am 
interested in you getting what you think you're getting.  I am not in 
sales, I am involved in support for this platform.  I will hear about it 
if something is not up to expectations or goes badly.

John Gill

On 1/27/12 5:13 PM, Jiri Prochazka wrote:
> John,
> thank you for a reply. I am interrested in unicast traffic only, no L3,
> no QoS requirements, low-latency is not needed, 10G ports only. Switches
> would be used for a standard Internet traffic flows.
> I am really interrested in these switches, but I don't want to buy a pig
> in a poke..
> Regards,
> Jiri Prochazka
> Dne 27.1.2012 22:19, John Gill napsal(a):
>> Hi Jiri,
>> The bandwidth to the fabric is dedicated and the expansion modules
>> have their own forwarding engines on them, so they are no different
>> than the base ports except that they can be swapped out.
>> What kind of traffic are you interested in running? Unicast,
>> multicast, QoS requirements? Do you have low-latency requirements? 10G
>> or 1G? Do you know how much buffering you would need with your traffic
>> flows? Or is this mostly fact finding for now? Let me know if you have
>> any specific rumors as well.
>> Regards,
>> John Gill
>> cisco
>> On 1/26/12 8:30 PM, Jiri Prochazka wrote:
>>> Hi,
>>> we are considering investment in a few Nexus 5596 switches. All Cisco
>>> documents say it has 96 non-blocking 10G ports (for L2). Is it _really_
>>> true? Can the switch reach throughput of 960 Gbps regardless the traffic
>>> distribution? Is't there some hidden limitaion, which is not presented
>>> by Cisco? :-) I've heard some rumors about this, but nothing particular.
>>> First thig which comes to my mind is a doubt, if all three expansion
>>> modules really do have 160 Gbps connection to the fabric..
>>> Thank you for comments,
>>> Jiri
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