Why a coreswitch?

[Freihafener]

I got a simple question - and a lack of a good answer.

My manager asked me if we really need a coreswitch (like a cisco 4506). Does anyone could give me some more reasons why to use a core in a small / midsize LAN?

Our infrastructure at this office for short (former server room):

About ten application servers (GigabitEth) and 300 clients (ThinClients without VOIP), a 4506 core / WAN Gateway and 14 switches in the stories.

Is the only reason to use a core to provide fiber uplink ports? I would guess that a 2960 or a 3560 in combination with some kind of fiber port switch would have enough performance to do the job - or am I wrong? What is the clue of a core?

[garapoglou · Accepted solution]

Hi,

Having a core switch always depends on the network. On small networks with a couple of servers and a few clients, there's no actual need of a core switch. But there has to be at least one core switch on larger ones. Most of the times there are two of them for redundancy purposes.

In medium/large networks with multiple VLANs, we usually arrange the VLAN management to a different switch to reduce the workload of the core switch. This is a small example of how important its job is.

One of its duties is to provide fast uplink speed to the distribution and access switches. I'm not sure whether connecting smaller switches using fiber ports would not affect the network without a core switch. It's something you should check it out during production.

My guess is you could try it if your network has no VLANs, no huge workload or large file transferring.

Best regards,

Giorgos 

[Latchum Naidu]

Hi,

Core switch is a switch, usually a L3, which is placed in the core layer of a hierarchical network model. The most important function of core switch is to switch packets as fast as possible.

Interfaces with enough port to terminate all links from the other modules in the neetwork like the distribution layer switches, the server farm module, the enterprise edge module and so on

Generally medium to large sized networks are commonly built using a 3-layer hierarchy: Access, Distribution and Core. The access switches are where end user PCs and workstations and printers get connected and where some security and QoS takes place. The distribution switches are used to aggregate multiple access switches as well as take care of routing, filtering, access lists, etc. The core switches are simply there to forward data frames as fast as possible. The core switch(es) can also be designed using L2 or L3 protocols, and the core is designed to be as fault tolerant and highly available and as fast as possible.

Please rate the helpfull posts.
Regards,
Naidu.

[Freihafener]

Hi Naidu,

thanks for your detailed answer! I have got some experience with network administration, but this is a question I never thought about in detail. So Layer 3 functions, availability, reliability, scalability and performance (speed) are the main criteria for sure - but in this case for that purpose I guess a 3560 would have enough power to do the job even with more than one VLAN. I think you will never notice a difference to a 4506.

[garapoglou]

Hi,

In other words, a 4506 would be too much for your network if you ask me.

Best regards,

Giorgos

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

What's often overlooked is the reason for hierarchal network designs was and is for scalability.  When you're unable to keep everything on one device, as you add devices a hierarchal design minimizes hops between devices.  Further as you add devices, you might have different feature capabilities to reduce overall costs.

Given these considerations, a large network using 3 layers generally has an access or edge layer that's dumb (i.e. L2 switches; today perhaps L3 too), a distribution layer with intelligence (i.e. L3 with other features), and core or backbone layer that's really fast (to handle the combined load) which might be dumb (i.e. L2; switched core, not as common today) or with intelligence (i.e. L3; routed core).

If you didn't need 3 layers to support your network, 2 layers might be used, often called a collasped core or collasped backbone since the distribution and core layers are combined.

Current high density and high performance network devices, really change the boundaries of what's small vs. what's large.

Consider if you had only 4 port devices, you could have 4 hosts on one device, support 12 hosts (two layers) on 5 devices, and for more than 12 hosts you would need to start a 3rd layer (all this assuming you're using hierarchal design).  However, if you had 48 port devices, would you still have two layers for 12 hosts?

Perhaps than a good answer to your question, small/medium/large depends on number of hosts and available equipment and its capabilities.  Small fits on one layer, medium on two layers and large on three layers, the latter having a "core".

[Latchum Naidu]

Hi Giorgos,

Of course a 3560 would do the job for you including routing, vlan and etc.,
But it depends on the size of network you have in other words how many interface do you need and the hardware levels of the coreswitch you need to handle the data traffic.

Please rate the helpfull posts.
Regards,
Naidu.

[Freihafener]

Thanks for your answers - I thought as much.

Do you know how to estimate  the type of hardware I need in a  LAN? IMHO it is really diffcult to get  a configuration with is neither  under- nor oversized...

Out of my experience I would say that it is more a question of ports than bandwidth. Over time more and more servers got Gigabit NICs, but the fiber uplinks of the 48 port switches stick to 2 x gigabit fiber.

[Latchum Naidu]

Hi,

Do you know how to estimate  the type of hardware I need in a  LAN?
It is completely depneds on your network and user base and budget say for example I have 100 users at 1 site so I have two 3560's i HSRP and 5 2960.

And having a more ports available switch is a good idea when implementing network at first time because in future you may add more servers into network.

Please rate the helpfull posts.
Regards,
Naidu.