Determine network resources needed for implementing a VLAN based solution on a network

642-813 Exam topic numero uno here we go!

Topic Notes 

• Identify the number of users accessing the network
•  Identify applications that will run over the network (VoIP, IM, email)
•  For said applications, figure out the type of traffic pattern. Traffic will flow directly between users for IM and VoIP (except for call signaling). Traffic will flow from client to data center server for email
• Uplinks should be able to handle all users communicating at the same time
• Uplink sizing:
•  Uplinks connecting the Access layer to Distribution should have an over-subscription ratio of no more than 20 to 1
•    Uplinks connecting Distribution layer to Core should have an over-subscription ratio of no more than 4 to 1

Let’s put it to use

Using the guidelines/notes from above, let’s apply it to a real-world scenario.

Scenario:

ACME Inc. is building a branch office to support its outstanding sales growth. The business unit decides that 250 employees will be staffed at the new site. Each employee will be given a laptop with a standard image with an email and IM client.  Each user will also have a VoIP phone.

It is determined through traffic studies/packet captures (Wireshark) that each user will use up to 500Mbps during peak business hours.

The user population will be split between (2) Access layer switches, the layer 3 boundary will reside on (2) redundant distribution layer switches. Finally, the Distribution layer switches will interconnect to (2) redundant Core layer switches via routed link.

Each of the (2) port channels between the Access and Distro layer switches should have a minimum of (2) physical 1Gbps ports (4Gbps total). This requirement is calculated with 500Mbps (application requirement) X 125 users = 62.5 Gbps / 20 (over subscription ratio for Access to Distro interconnects) =3.125 Gbps.

Each of the Distribution switches must be able to support the load of both access switches (in the event that one of the distribution switches fails). (2) port channels interconnect Distro to Core. (2) 10Gbps links per port channel are needed. This is calculated by 500Mbps x 250 users = 125Gbps / 4 (over subscription ratio for Distro to Core interconnects) = 31.25 Gbps.