Unanswered Question
Oct 3rd, 2008

Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity to get an update for deploying Catalyst 4900M in data centers with Cisco expert Kenny Lei. Kenny is a Technical Marketing Engineer in the Campus Switching System Technology Group at Cisco, focusing on data center systems, mainly the Cisco Catalyst 4948 and Cisco Catalyst 4900M platforms. He has been at Cisco since 1997 and has worked in hardware development, software development. and marketing. He holds a bachelor of science degree in electrical engineering and computer sciences from the University of California, Berkeley.

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Hi Kenny, thanks for standing up for the good cause :) ... We have quite a times been advised by the local Cisco support to use Cat 4900M switches as top of the rack switches, and connect them to core/distribution switch over 10G interfaces. Here are my few concerns.

1. (From your intro) What are the major differences between 4948 and 4900M? which one is preferred in which scenario?

2. Considering a scenario of a flat network, how do you suggest its split into a 3-level network design using 4900 series switches?

3. why should one still prefer 4900 over 3500/3700 switch even if the uplink traffic is not more than a gig? Also, please explain in case of an etherchannel as uplink on 3x00 switches.

4. What is the best way to find out the subscription rate of all 4900 uplinks on a distribution switch like 6509?

5. What other benefits are there of using 4900 other than uplink=10 G.



klei Mon, 10/06/2008 - 10:02

Hi Mohsin,

1. Both Cat4948s and Cat4900M are full line rate non-blocking switches and are designed for Top Of the Rack. If you have 1G connection to the server and no plans to upgrade to 10G, and either 1G or 10G uplinks, Cat4948s are good fit here. If you have 1G server connections but plan to move to 10G, or mix of 1G and 10G server connections, then Cat4900M will give you the ability to accommodate these requirements.

2. A flat network works if you have a very small network but not some thing I would recommend. For a small network, the collapsed core and distribution might work. Cat4900M as core/distribution. But I strongly recommend the 3 tiers design: core, distribution and access. This modular approach provides many benefits - easy to grow, understand and troubleshoot. The Solution Reference Network Design guide on Campus and Data Center are great reference. You can find them at

3. Many customers deploy 3500/3750s throughout their networks. Whether it's due to their familiarity of the stackwise technology, or the pay as you grow business model, we often see networks designed with Stackables in the access and 6500s in the Dist/Core. The 4900 series is an optimized ToR switch for DC deployments. Very large DC customers are using the 4900 series as their ToR server switches. With its high number of 10GbE ports, some customers are also considering this platform as a L2 aggregation device for BoB (Bottom of the Basement) type deployments. The 4900 series family is a non-blocking, shared memory switch that yields ample resources for scalability/performance and can robustly handle momentary bursts of traffic with it's large egress buffering techniques. The 4900 series also provides extremely low latency in environments where sensitive traffic could suffer in times of congestion. These are essentially the ingredients required for ToR DC customers (Deep buffers, low latency, 10GbE uplinks, low power). Eweek has done some testing on the Cat4900M, and you can find the report here:

Etherchannel information on Catalyst swtiches

Etherchannel information on Catalyst 3xxx

4. Cat6500 and Cat4900 have different architecture, so there is no equivalent command on that. You can use Embedded Event Manage to monitor the traffic statistics on the uplinks. Like using the interface even detector to send a notification when the traffic rate reaches a number that you define. The following link has a collection of many user generated EEM scripts.

5. See item 3

You might already have this link, but just in case the following link can serve for your future reference.



klei Tue, 10/07/2008 - 07:52

Hi MJ,

This is supported since 12.2(46)SG release. We need to update the datasheet. Thanks for catching it.



klei Wed, 10/08/2008 - 12:00

Hi MJ,

That's correct. We are also working on updating the configuration tool to have the compact flash as an option when ordering a Cat4900M.



b.hsu Sun, 10/12/2008 - 20:34

I need some 1G fiber ports, do the Cat4900M provide that?

klei Mon, 10/13/2008 - 07:30


Yes. The 8port 10GE card provides you that flexibility. You can use a TwinGig module in the X2 slot for 1G connectivity. The TwinGig takes SPF (both Fiber and copper 1G) modules.



inch Mon, 10/13/2008 - 14:40

Hi Kenny,

How does the 4900M position itself in relation to the nexus 5000?



jaye15394 Tue, 10/14/2008 - 18:26


Can you please give latency numbers between switch ports? I'd like to analyze the port to port latency across 49xx, 3750E, and 6500 Series. I understand if you only have 4948 numbers available.



klei Tue, 10/14/2008 - 18:52

Hi Andrew,

Both switches are optimized for Data Center deployment. Typically, I see customer use Catalyst 4900M use as ToR for Ethernet access, and Nexus 5000 as ToR for 10GbE Unified Fabric access.



ianbow Wed, 10/15/2008 - 09:21

Can someone detail the span session limitation on these devices? Also would these work well in a DMZ design? If not which device would you recommend?



klei Wed, 10/15/2008 - 16:42

Hi Ian,

The Cat4900M has the same feature as the Sup6E on the Cat4500. The total number of SPAN session that is supported on the Cat4900M is 5. You can refer to the following link for addition information on Catalyst switches' SPAN features.

The Cat4900M support full layer3 functionality with 200K IPv4 routes. Without more information on your requirement, I won't be able to recommend a device. Please work with your SE with the requirements, and they will be able to recommend a device that fits your requirement.



rcierny Wed, 10/15/2008 - 15:54

Is there a timeline when multicast virtual routing and forwarding (VRF)lite is going to be supported on 4900M platform?

klei Wed, 10/15/2008 - 16:57


I don't have the exact date. The feature is currently in EFT, it will be available with 12.2(50)SG release.




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