Bandwidth Calculation

Greeting Gentlemen,

We have started a new project where a new access switch will be added to an existing Network. One of requirement is evaluating the Core and distribution switch and making sure they are adequate. My question is: how to do the bandwidth calculation on the Core and Distribution is there a certain formula.

Appreciate your kind support

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fredrikjj

There is no general formula since it all depends on what kind of traffic you expect from the users, how many users you have, and how heavily you can oversubscribe the uplinks between access and core/distribution. The access switch itself will most likely have 1 gigabit ports to the clients if it's for general office use since many vendors don't even sell 100 Mbps anymore, but that doesn't necessarily mean that the uplinks to core/distribution need to exceed that. In a typically office environment where people aren't downloading a bunch of stuff and streaming HD video you could easily oversubscribe the access layer at 100 to 1 or more. The main benefit to this is that you can just run a cheap 1 Gbps uplink and can avoid spending money on 10G interfaces. You could also potentially get a cheaper switch that doesn't even support 10G. An alternative to this would be to get a switch that supports 10G, but only use 1G to begin with and then upgrade to 10 if it's needed in the future due to some change in the requirements. Or you could just add additional 1 gbps links as the bandwidth requirements increase and bundle them with some aggregation protocol like LACP.

mralhashim83

Thanks fredrikjj for your response.

The uplink from the distribution to the core switch is 10 G. Is it necessary to know the bandwidth utilization or no need since the Qos already configured.

Thanks in advance

tomtom1

mralhashim83 wrote: »

Thanks fredrikjj for your response.

The uplink from the distribution to the core switch is 10 G. Is it necessary to know the bandwidth utilization or no need since the Qos already configured.

Thanks in advance

When reevaluating the existing network, it is never unwise to know the current bandwidth utilization.

mralhashim83

tomtom1 wrote: »

When reevaluating the existing network, it is never unwise to know the current bandwidth utilization.

why it's unwise?

networker050184

I think what tomtom1 was getting at is that you should know the bandwidth utilization. One story I always remember about this is a group of systems admins swore up and down they needed 10G connectivity. Their applications need it! They finally convinced management to spend a fortune to upgrade that portion of the network (new SUPs, LCs, XFPs etc.) and after it was all built out they never went over a couple hundred megs at peak.

Knowing what you need is important to set your budget!

tomtom1

networker050184 wrote: »

I think what tomtom1 was getting at is that you should know the bandwidth utilization. One story I always remember about this is a group of systems admins swore up and down they needed 10G connectivity. Their applications need it! They finally convinced management to spend a fortune to upgrade that portion of the network (new SUPs, LCs, XFPs etc.) and after it was all built out they never went over a couple hundred megs at peak.

Knowing what you need is important to set your budget!

My point exactly. Besides budget, it creates more realistic views of your network components.