[c-nsp] Nexus 2000 vs Catalyst 4948 for access layer

Brad Hedlund brhedlun at cisco.com
Mon Feb 1 23:56:50 EST 2010

True, the Nexus 2000 does not locally switch, but lets explore that for a second...

1) a typical enterprise Data Center is running applications that are not latency sensitive, where latencies in the 10s of microseconds are perfectly OK and nobody is really counting anyway. Only in the small minority of Data Centers running high frequency trading, grid computing, or some other ultra low latency application, every *nanosecond* matters and local switching with fewer hops is of paramount importance. Furthermore, these applications are quickly migrating away from 1GE to 10GE attached servers for the obvious low latency advantages.

2) the Nexus 2000 has 4x10GE uplink bandwidth versus the 2x10GE uplink for 4948.  This results in a possible 1:1.2 oversubscription ratio for Nexus 2000 to handle the additional uplink load that may otherwise not be present on a 4948.

3) The upstream Nexus 5000 implements cut-through switching, and the Nexus 2000 itself also uses cut-through for frames entering on 1GE and egressing on 10GE.  The two combined often results in port-to-port latencies similar to a Catalyst 6500, even without the "local switching".  If you are comfortable with your Catalyst 6500 local switching latencies, you can expect similar performance from a Nexus 2000/5000 combination.

Brad Hedlund, CCIE #5530
Consulting Systems Engineer, Data Center
bhedlund at cisco.com

On Jan 31, 2010, at 5:25 PM, David Hughes wrote:

> On 29/01/2010, at 6:54 AM, Livio Zanol Puppim wrote:
>> Can anyone please tell me the advantages of using Nexus 2000 over Catalyst
>> 4948 as access layers switches?
>> Using Nexus 2000, I have to use at least 2 ports at my Nexus 5000, that
>> could be used by servers with 10GbE/FCoE servers.
> The N2K does no local switching so if you have any east-west traffic between ports on the same switch you'll be better served by a more "traditional" access switch.  Naturally the N2K offers centralised management etc etc but that may or may not be of interest depending on the size of your deployment.
> David
> ...
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