Data Center LAN Migration Guide - Juniper Networks

Data Center LAN Migration Guide
• The QFX3500 is also preferred for 10 Gigabit data center designs and for those deployments requiring FCoE and
Fibre Channel Gateway functionality.
• The QFX3500 also is a building block to Juniper’s QFabric technology to deliver a data center fabric which enables
exponential gains in scale,performance and efficiency.
The EX4500 is typically deployed in smaller Enterprise as a data center aggregation switch or in a smaller campus
environment. When the requirement is for GbE server connectivity, the EX4200 would be the platform of choice, where
up to 480 GbE server connections may be accommodated within a single Virtual Chassis.
For 10 Gigabit connectivity, the QFX3500 enables IT organizations to take advantage of the opportunity to converge
I/O in a rack. Servers can connect to the QFX3500 using a converged network adaptor (CNA) over 10Gb channeling
both IP and SAN traffic over a single interface. The QFX3500 devices will in turn connect directly to the data center
SAN Array functioning as a Fiber Channel (FC) gateway. Additionally, the solution can support operating the QFX3500
as a FC transit switch and connect it to an external SAN director that will fulfill the FC gateway functionality.
Design Options and Best Practices: New Application/Technology Refresh/Server Virtualization
Trigger Events
When deploying a new access layer as part of this trigger event, there are issues related to uplink oversubscription,
STP, and Virtual Chassis. Understanding design options and best practices for each of these topics is important to
a successful deployment. This next section will cover access layer migration for Gigabit connected servers. The next
version of the data center Migration guide will include 10 Gigabit as well as Fibre Channel convergence best practices.
Tunable Oversubscription in Uplink Link Aggregation
In legacy networks, oversubscription is an ongoing issue, leading to unpredictable performance and the inability to
deploy or provision a new application with confidence. Oversubscription typically occurs between the access and the
core/aggregation switches (on the access network uplinks).
Juniper provides a tunable oversubscription ratio of from 1 to 12 between the access and the core with the EX4200
Virtual Chassis. Up to 10 EX4200 Virtual Chassis systems can be configured together to perform and be managed as
one device. Each Virtual Chassis supports up to 48 GbE connections and up to two 10GbE uplinks.
A full configuration of 10 EX4200s has up to 480 GbE ports + 2 x (m) x 10GbE uplinks, where m is 1 to 10. The
oversubscription ratio is tuned by adjusting the number of units in the Virtual Chassis, the number of GbE ports, and the
10GbE uplinks. An oversubscription ratio of 1, delivering full wire rate, is achieved when there is no greater than 2 units
in a Virtual Chassis configuration and 40 gigabit user ports provisioned. An oversubscription ratio of 12:1 is achieved if
there are 480 GbE ports and 4x10GbE uplinks.
The target oversubscription ratio is always going to be based on the applications and services that the Virtual Chassis
is expected to support. It can be easily adjusted by adding or removing 10GbE uplinks, or by increasing or reducing
the number of member switches in the Virtual Chassis. For example, a 5 to 6 member Virtual Chassis using two to
four 10GbE uplinks delivers oversubscription ratios between 7:1 and 12:1. Or, a 7 to 8 member Virtual Chassis using 4
10GbE uplinks, two in the middle and two at the ends, delivers oversubscription ratios between 8:1 and 9:1. While these
oversubscription levels are common, the most important point is that they can be adjusted as needed.
Spanning Tree Alternatives for Access Layer Insertion Point
STP offers benefits to the data center, but it is also plagued with a number of well-known and hard to overcome issues.
These include inefficient link utilization, configuration errors that can potentially bring an entire L2 domain down, and
other problems. To avoid these issues, enterprises may consider alternative architectures to STP when inserting a new
POD into the network. These can include an inverted U design, Redundant Trunk Groups (RTGs), and L3 uplinks.
Inverted U Design
An enterprise can create an STP-free data center topology when using an L2 domain to facilitate virtual machine
mobility through the way it connects servers to an access layer switch. An inverted U design can be used such that
no L2 loops are created. While technologies like STP or RTG aren’t required to prevent the loop, best practices still
recommend provisioning STP to prevent accidental looping due to incorrect configuration.
Copyright © 2012, Juniper Networks, Inc. 33