Juniper Virtual Chassis Technology: A Short Tutorial

Victor Lama Fabric Specialist – LE Northeast Region August 2010

What if…?

What if your company could drastically minimize the complexity of managing your data center network by

being able to take multiple network appliances and manage them as if they were just one device?

What if there was a modular network switching solution that offered dual routing and switching engines with

graceful failover in the event of an outage, as well as in-service hardware replacement and code upgrades?

What a tremendous impact that would make toward providing high availability to mission critical applications

and services!

What if network architects could finally do away with the design complexities of deploying the Spanning Tree

Protocol by virtualizing multiple layers in the data center? No more worries about interoperability of STP,

MSTP, RSTP, PVRSTP, CST, across vendor platforms, and no more blocking and wasting half your data center’s

cross-sectional bandwidth!

What if those who hold your company’s purse strings could scale your network CAPex as the business need

arises, instead of just having to make large capital investments up front?

With Juniper’s Virtual Chassis technology, all the above, and more, are possible.

What is Virtual Chassis Technology?

Virtual Chassis (VC) is a network virtualization technology offered in several models of Juniper Ethernet

switches, such as the EX4200. With VC, between 2 and 10 physical Ethernet switches can be “stacked” to form

a single logical form factor with a unified control plane and configuration file, as well as a single OS instance

that operates across the entire stack. Route and switch engine redundancy are provided by the VC master and

the backup through the creation and maintenance of synchronized forwarding tables and the exchange of

stateful protocol information.

The VC can span anywhere from 5 meters in height and breadth to 50 km across an entire campus or regional

area! Using the EX4200 as an example, between 24 and 480 10/100/1000 Mbps ports can be managed as if

they belong to one VC that supports multiple VLANs, a non-blocking architecture and full cross-sectional

bandwidth utilization. Connecting the members of a Virtual Chassis in a ring topology results in a total virtual

backplane speed of 128Gbps– 64Gbps in each direction.

A key factor to understand is that Virtual Chassis technology deploys a direct path algorithm known as the

Virtual Chassis Control Protocol (VCCP) for optimal traffic flow. Forwarding tables are built with the aggregate

intelligence of all the members of the VC, thereby ensuring that traffic takes the shortest path to its

destination.

VC is one of the core enabling technologies of Juniper’s vision for the data center of the future, otherwise

known as Stratus. The foundational concept behind Stratus is to replicate the simplicity of a single fabric in a

single switch chassis across the data center – or between data centers! The result is a resilient low-latency

data center fabric that has the built in flexibility to support converged networks and virtualized workloads in a

variety of different topologies.

Building a Virtual Chassis

As noted above, the physical members of a VC can be collocated in a configuration that spans no more than 5

meters between stack elements. A VC configuration consisting of adjacent switches interconnected with

special 0.5 meter, 1.5 meter, 3 meter, or 5 meter VC port cables is called a dedicated configuration. A VC

configuration interconnected via Gigabit Ethernet or 10-Gigabit Ethernet uplink ports across distances up to 50

km is called an extended configuration.

Figure 2 shows a rear view of a Juniper EX4200 Ethernet switch and the VC Ports (VCP) that interconnect the

different VC elements. Each VCP offers 64Gbs of throughput for data traffic as well as protocol state

information to maintain synchronized control and data planes between the Master and the Backup Route-

Switch Engines (RSE).

Once the VCP ports are cabled, they are automatically enabled to provide the switching backplane for the

dedicated chassis configuration.

To extend the VC configuration across a campus or regional area, the EX-UM-2X4SFP 10Gbps module, with

dual 10G ports, can be deployed and configured to carry VC control information over an aggregated link that

provides up to 40Gbps of throughput – 20Gbps in each direction.

Virtual Chassis Member Roles – Dedicated Chassis

Each member in a Virtual Chassis configuration is assigned a specific role. A role determines the functions the

member performs in the configuration. One member is assigned the master role and is responsible for

managing other members in the Virtual Chassis configuration.

Another member is assigned the backup role and takes over the master role if the master switch fails. All other

members are assigned the line card role. The system executes a mastership election algorithm to determine

member roles.

Virtual Chassis Roles – Extended Configuration

In an extended configuration, the master and the backup should be in different locations as part of dedicated

chassis configurations. Moreover, the extended VCP connections can consist of gigabit, ten gigabit or

aggregated Ethernet port connections for higher bandwidth requirements.

Cabling Options

There are three different methods for connecting members of a Virtual Chassis. These are the daisy-chained

ring, the braided-ring and the extended configuration. The daisy-chained and braided ring methods are

deployed in dedicated chassis configurations, with the braided-ring offering a greater maximum distance

between the first and last member of the stack.

See figure 6a and 6b below.

As noted earlier, an extended chassis consists of smaller dedicated virtual chassis interconnected by Ethernet

ports in a singular or bundled fashion. This capability provides the flexibility to manage an entire campus LAN

as one management plane with one IP address and a singular control plane that allows for automatic

configuration and code upgrades upon introduction of a new member to the VC. This is known as dynamic

installation.

See figure 6C below.

Virtual Chassis Deployment Options

Data Center Top of Rack (ToR)

The data center top of rack deployment is suitable for environments in which members of the Virtual Chassis

configuration are collocated with servers in the same rack.

A single Virtual Chassis configuration consisting of multiple switches in the same rack simplifies management

by reducing the number of managed devices. This deployment also provides servers with the capability of

configuring NIC teaming (LAG) to multiple members of the same Virtual Chassis configuration, increasing the

total server network bandwidth while providing server link redundancy.

See figure 7 below.

As figure 8 shows, in a Dell m1000e blade server deployment that includes M-series stackable blade switches,

virtualization of the edge and access layer can be achieved, thereby removing the need for the deployment of

the Spanning Tree Protocol. Multiple physical connections between the blade switches and the ToR VC will be

seen as one logical link by each virtual layer. This allows for a non-blocking rack architecture and full utilization

of available cross-sectional bandwidth.

Single Virtual Chassis Spanning Entire Row

Depending on server density and spacing the ToR solution can be extended to support an entire row of

cabinets – 10 cabinets if one switch is placed at the top of the rack or 5 if the design calls for a self-contained

modular cabinet that can be removed or deployed at will. In the latter, all the server-to-ToR cables will be

confined to the cabinet. The ToR switches shown below all belong to the same Virtual Chassis.

End of Row (EoR)

Because the EX4200 Virtual Chassis can support layer 2 and layer 3 deployments, it can also play the role of an

end of row solution. Typically, the EoR is a layer 3 aggregation/distribution layer that includes the deployment

of transparent data center services, such as load balancing, firewalls, SSL offloads, etc.

Campus LAN Wiring Closet(s) and Campus Aggregation

Hopefully by now, the concept should be clear: the Virtual Chassis technology allows the network architect to

be extremely flexible and creative in deploying design solutions. A VC can be deployed in many different

topological scenarios and in different network roles. In a campus environment, a VC can be formed in a single

wiring closet or in several closets across a user-floor(s). The access layer and the campus distribution layer can

both exist as VC instances. Wiring closets that are more than 5 meters apart can be connected via gigabit, 10-

gigabit and aggregated Ethernet connections, just as they were in our data center examples.

The campus aggregation layer can consist of a single Virtual Chassis instance or multiple instances, depending

on the traffic requirements. The thing to keep in mind is that deploying separate VC instances in the

aggregation layer will require the deployment of STP between VCs and the access layer, thereby mitigating the

benefit of virtualizing network layers.

See figure 11 below.

Summary

Deploying a Virtual Chassis solution in a high performance data center reduces the complexity of switch

hardware installations, OS upgrades, configuration tasks, and management of the switched fabric. Moreover,

virtualizing multiple layers is one of the necessary steps toward the creation of a “flat” data center network in

which all L2 links are utilized and multiple layers of packet processing are eliminated. This will minimize

latency, remove the need to deploy L2 loop mitigation technology, and create a non-blocking fabric with an

average x2 increase in available cross-sectional bandwidth across the data center.