Campus lan and Wireless lan solution Design Guide

 
Example oversubscription ratio – single access-layer switch
Figure 4. 
The maximum potential bandwidth usage of the switch ports would be 12 x 10 Gbps = 120 Gbps plus 36 x 
1Gbps = 36 Gbps, for a total 156 Gbps. The maximum uplink oversubscription ratio would be 156 Gbps : 20 
Gbps or 7.8:1, assuming all mGig ports were operating at 10 Gbps.
More realistically, you may have the following actually connected to the switch: 
● 
8 Catalyst 9100 Series APs operating at 5 Gbps connected to the switch ports 
● 
32 Cisco IP Phones and/or end-user devices (PCs, Mac’s etc.) operating at 1 Gbps connected to the 
switch ports 
● 
8 Unused ports for future expansion and capacity 
The actual potential bandwidth usage of the switch ports would be 8 x 5 Gbps = 40 Gbps plus 32 x 1 Gbps = 32 
Gbps, for a total 72 Gbps. Therefore a more realistic view of the oversubscription ratio is 72 Gbps : 20 Gbps, or 
3.6:1.
This configuration provides for additional capacity, in that you have an additional 2 x 10 Gbps unused uplinks as 
additional devices require mGig port speeds, as devices transition to 10 Gbps speeds, and as you expand 
capacity in a switch stack configuration 
Switch stack configurations 
Migrating to a switch stack is an effective, flexible, and scalable solution to expand network capacity at the 
access-layer. The benefits of a switch stack are as follows: 
● 
The switch stack behaves as a single device (characteristics and functionality of a single switch) 
● 
The switch stack allows expansion of switch ports without having to manage multiple devices 
● 
Switches can be added or removed from the switch stack without affecting the overall operation of the 
switch stack 
● 
Depending upon the configuration of the switch stack, it can continue to transmit data even if a link or 
switch within the stack fails 

---

© 2020 Cisco and/or its affiliates. All rights reserved. 
Page 10 of 76
When adding additional access layer switches in a stackable configuration, you should design the switch stack 
with the desired oversubscription ratio both during normal operations, and if there is a failure of a switch within 
the stack.