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Advantages of 3-layer architecture over 2-Layer

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Feb 9th, 2009
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Dear All,

Can anyone please explain me the advantages of 3-Layer architecture ( Core-Distribution-Access) over 2-Layer Architecture ?

Thanks and Regards.

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Joseph W. Doherty Mon, 02/09/2009 - 04:29
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Assuming your thinking just physical hierarchal topology, it's really about scaling a network to support a number of hosts. 2 layers support (about) X squared ports, where X is number of ports per device, and 3 layers support (about) X cubed ports.

Davy Ad Mon, 02/09/2009 - 08:24
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Hi Mangesh,

It makes you understand your Infrastructure better and against trouble shooting you would be able to know where/what you need .



Leo Laohoo Mon, 02/09/2009 - 13:03
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Financially, Layer-2 Architechture "will do the job". Personally, that person needs to be take out and shot!

Technically, a Layer-3 Architechture will allow easy trouble-shooting by separating or segmenting the network based on function and topology.

If it's a small site, a collapsed Layer-2 (Core & Distribution, Access or Core, Distribution & Access) could be used.

davebarus Sun, 02/22/2009 - 05:36
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The CDA model (Cisco's 3 Layer Hiearchical model) is typically used in a medium to large network - although, it can also be used in a small network, it just might not be financially feasible depending on the company's budget. The 3 layer architecture will also help allocate resources better throughout the network. For instance, the core can do its job and ensure high speed packet delivery, the distribution switches can focus on things like routing between VLANs (or subnets) and QoS, while the access layer can focus on delivering data to the end users. This model also allows much better scalability than the two layer model.

The collapsed core architecture (2 layer) is mostly used in small networks. It may be used for perhaps, a small branch office. It takes the above CDA model and collapses it into 2 layers. Either the core/distribution and access model or the core and distribution/access model. Depending on the size of the network, it might be a wise financial decision to take this route instead of the 3 Layer Architecture. Although, from a technical standpoint, the 3 layer model is the way to go.

Here is a link that may provide some more insight:



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