How many spare ports on an access layer switch?

[Solomon Sands]

Hi All,

A question on design.  I'm looking for a best practice/design on the subject.  I've worked on an NDS that specified 10% of port density be reserved for spare use.  By that math, for a 24 port switch that would leave me with 2 or 3 spare ports.  My current project has the access layer as single stack 3850s so 22 ports will not overrun the backplane, I just wanted to confirm that such a design parameter exists at all?

FWIW, I'm aware that Cisco recommends 1Gig uplink for every 20 downstream ports, thus 20 ports with 4 spares and 1 uplink would be the threshold of this recommendation, or rather ~16% of port availability (and a more streamlined value of 15% meets this on 24-ports as well)

[pwwiddicombe]

Several factors to consider.  For large switches, 10% is probably a little low; for smaller switches you'd be cutting it tight ?

1.  How easy is it to get additional budget later?

2.  Any planned expansion or potential expansion?

3.  Printers?  Network attached cameras?  Spare ports for special projects or meeting rooms?

[devils_advocate]

I did a project where we specified 10% spare switchports for future use.

Mid way through the project we were putting in extra swtiches..

To be fair, the project planning and information provided was poor during the design stages but it made me realise that 10% is not enough. I would try 20-30% if it were me.