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VCStack

Resilient enterprise networks with Virtual Chassis Stacking

Today's enterprises rely on Information Technology resources

and applications, for accessing business-critical information and

for day-to-day work. A high availability infrastructure is no

longer a luxury; maintaining resource availability and data

security is now of paramount importance.

Productivity is adversely affected when any of the following

occur:

■

loss of access to the Internet

■

loss of access to internal servers and intranet

■

loss of IP telephony services

■

oss of customer access to public servers

It is vital, even for a small enterprise, to keep high availability

considerations at the center of network design. The availability

of network resources is maximised with an Allied Telesis Virtual

Chassis Stacking (VCS) solution, providing continuous and

immediate access to information when it's required.

Technology comparison

To fully appreciate the benefits of the VCS solution offered by

Allied Telesis, it is necessary to compare this technology with

the standard high availability solution that it replaces.

Prior to the advent of the VCS solution, high availability in small-

medium enterprise networks was achieved by provisioning

redundant links and redundant routers. In normal operation,

bandwidth and routing power would sit idle in the network.

Allied Telesis now provides a truly resilient network. In normal

operation, all bandwidth and all routing power in the network is

fully available for use all the time. If a link or device fails, some of

the bandwidth or forwarding power will be lost, but the

network will still be fully operational and will continue to fully

utilize the remaining resources.

Allied Telesis Solutions:VCStack

The early solution: Virtual Router

Redundancy (VRRP) and Spanning Tree (STP)

VRRP

Device

(Virtual Router

redundancy

Redundancy

Protocol)

Back-up data paths through the network have always been

desirable in case of link or hardware failure. Before VCS, the

standard solution was to provide redundant links in the

network, with STP blocking switch ports to ensure that there

were no active loops.

Over the years, STP has evolved to provide faster failover and

to take better account of VLAN topologies by load-balancing

network traffic. However, the fundamental operation of STP

has remained the same for over 15 years.

Layer-2 path redundancy in the form of STP is often

accompanied by Layer-3 device redundancy in the form of a

virtual gateway. VRRP provides automatic backup, enabling

multiple routers or switches to share a virtual IP address that

serves as the default LAN gateway. If the master fails, the other

devices take over the virtual IP address.

"Before Virtual Chassis Stacking (VCS), the

standard solution was to provide redundant

links in the network with STP..."

STP

Path

(Spanning Tree

redundancy

Protocol)