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Enterprise Ethernet gets a sharper edge
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Highly reliable, efficient, and manageable Ethernet-based enterprise networks and data
centers provide vital support to the growing number of business-based IT applications,
including those relating to finance, administration, production, and websites.
Network reliability is crucial
Legacy enterprise Ethernet had fewer ports and services, and IT applications were
largely independent of networks. Enterprises simply required a basic network that was
able to connect to ports and devices across a single node, and connect devices over a
single link. This type of network was immune to the broadcast storm caused by network
loops, yet its single node structure can hardly provide reliable backup when the network
fails.
With technological progress and society's increasing sophistication, enterprises
increasingly rely on IT and information networks to conduct business, and in this area,
inherited enterprise networks are proving to be inadequate. Today, multi-node,
multi-link, and ring-based networking models have become the mainstream modes to
enhance reliability; however, these networks come with loops, especially those that
cover large campuses and data centers.
Ethernet's broadcast network architecture is susceptible to broadcast storms. Statistics
reveal that campus and data center networks experience an average of 10 to 20
problems, more than half of which seriously affect network performance. While
spanning tree protocol (STP) and enhanced STP can eliminate broadcast storms, these
protocols negatively affect network configuration and O&M, and are unsuitable for
large networks. With loops, networks with STP are unreliable, unmanageable, and
suffer low QoE.
Existing network construction prioritizes the prevention of loops and broadcast storms
to deliver a highly available, efficient, and manageable network. To realize such a
network, Loop-Free Reliable (LFR) Ethernet embodies the optimum solution.
LFR Ethernet giving an edge
Underpinned by strong expertise in All-IP and Ethernet switches, Huawei has
developed an LFR Ethernet solution that enhances network reliability, shortens
troubleshooting time, and increases bandwidth utilization. The solution integrates
switch clusters, stacking, and link-bundling technologies, and is as easy to deploy as a
Layer 2 network. Compared with a network featuring redundant links, LFR greatly
simplifies network O&M.
As Fig. 1 (see PDF) shows, the LFR Ethernet removes loops and the STP. The terminal
server or PC connects with two access switches through two bundled links to enhance
access reliability. Two (or more) access switches are stacked, and aggregation switches
are arranged within a cluster switching system (CSS). Multiple access and aggregation
links are then bundled to increase network bandwidth and reliability, and loops are
eradicated between the access and aggregation layers. Switches are networked in the
same way from the aggregation to core layer.
Fig. 1 (see PDF) illustrates that the LFR network resembles a tree with core nodes at the
root, and network traffic normally flows from the leaves to the root nodes. If an access
switch fails, another in the stack automatically takes over and forwards all the traffic
without affecting the aggregation devices. Equally, if an aggregation switch fails,
another in the cluster automatically responds to forward traffic without influencing the
access and core devices. Core switch failure also invokes the same procedure.
The reliability, bandwidth utilization, and maintenance afforded by this design are
superior to dual-link and dual-node. Maintaining an LFR Ethernet is as simple as
maintaining a single-link, single-device network. Unlike a conventional Layer 3
routing network, the LFR Ethernet is free from complex routing protocols and IP
addresses.
Given the crucial role of switch-clustering and stacking within this network structure,
leading vendors generally apply stacking technology to box access switches, and this is
now a common feature in Intranet applications.
To meet the growing demand for network bandwidth, the capability to cluster
aggregation and core devices is essential. The Huawei LFR solution utilizes cluster
technology to support a non-blocking switch between clustered frames, and the main
control boards of the clustered devices are directly connected. This enables the
non-blocking switch to function. It also eliminates the need to perform secondary
switching, which is otherwise required for a cluster with interface boards. This
dramatically improves the reliability, efficiency and QoE of the cluster system, and
curtails CAPEX given that slots are not occupied. Under the local traffic forwarding
model, a device forwards traffic to a directly connected upper-layer device, which
boosts efficiency without generating useless traffic.
Three steps to network restructuring
Enterprises can transform existing campus and data center networks into LFR networks
by gradually reducing Layer 2 loops and constructing a large and robust LFR Layer 2
network.
Step 1: Plan feasible network topology that avoids single point failures.
On key nodes, two devices are deployed to realize redundant backup and thus prevent
network and services from being affected by single device failures. Access switches are
connected to servers, and redundancy is applied to aggregation switches, core switches,
and network links. The network links should also be dual-homed to two devices. This
step eliminates single point failures, but results in a massive number of Layer 2 loops.
Step 2: Restructure the access layer to optimize bandwidth utilization in servers,
simplify network structure, and eradicate loops with LFR.
Large numbers of access devices create a heavy workload when restructuring a network,
but a gradual approach can minimize the impact on services. Generally, individual
users connect to one switch, which requires no restructuring and allows the focus to be
on the campus and data center servers.
Fig. 2 (PDF) shows that the servers generally connect to two access switches through
two adaptors, and work in active/standby mode. It is preferable to stack two adjacent
access switches, and bundle the server access links into one virtual link. Two network
adaptors can then share the server load to fully utilize bandwidth.
Step 3: Restructure the core and aggregation layers to simplify network structure.
Two adjacent aggregation switches cluster into one logic device that transforms
triangular and box loops into a tree under the root node to eliminate the loop problem.
Multiple upstream links for a single access or aggregation switch are bundled into one
entity, which simplifies the network structure, as Fig. 3 (see PDF) shows.
A network usually has much fewer aggregation and core nodes than access nodes.
When planning to restructure networks, enterprises are usually flexible in terms of time
and budgets. The process can be completed as an all-at-once project, or in phases,
starting with access layer.
These three steps simplify legacy link protection switching by performing switching
between two connected devices over a bundled link, which in turn eliminates the need
for a complex protocol to control link monitoring and switching. Additionally,
switching between devices in a single clustered node replaces conventional switching
between redundant network nodes; this significantly enhances E2E service reliability.
Moreover, the solution reduces the number of physical nodes by over 50% to yield a
much simpler network structure and reduce management requirements.
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