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DATA NETWORK & INFRASTRUCTURE

Everything you need to know about building networks correctly

W

hile almost every part of a modern datacenter

can be considered mission-critical, the network
is the absolute foundation of all communica-

tions. That’s why it must be designed and built right the first
time. After all, the best servers and storage in the world
can’t do anything withouta solid network.

To that end, here are a variety of design points and best
practices to help tighten up the bottom end.

copper runs or through server aggregation switches in
each rack. This decision must be determined site by site,
due to the distance limitations of copper cabling.
Either way, it’s cleaner to deploy server aggregation
switches in each rack and run only a few fiberlinks back
to the core than try to shoehorn everything into a few huge
switches. In addition, using server aggregation switches
will allow redundant connections to redundant cores,
which will eliminate the possibility of losing server com-

Core considerations
The term “network” applies to everything from LAN to
SAN to WAN. All these variations require a network core,
so let’s start there.The size of the organization will determine the size and

munications in the event of a core switch failure. If you can
afford it and your layout permits it, use server aggregation
switches.
Regardless of the physical layout method, the core
switches need to be redundant in every possible way:

capacity of the core. In most infrastructures, the datacen-

redundant power, redundantinterconnections, and

ter core is constructed differently from the LAN core. If we

redundant routing protocols. Ideally, they should have

take a hypothetical network that has to serve the needs

redundant control modules as well, but you can make do

of a few hundred or a thousand users in a single building,

without them if you can’t afford them.

with a datacenter in the middle, it’snot uncommon to find

Core switches will be responsible for switching nearly

that there are big switches in the middle and aggregation

every packet in the infrastructure, so they need to be bal-

switches at the edges.

anced accordingly. It’s a good idea to make ample use

Ideally, the core is composed of two modular switch-

of HSRP (Hot Standby Routing Protocol) or VRRP (Virtualing platforms that carry data from the edge over gigabit

Routing Redundancy Protocol). These allow two discrete

fiber, located in the same room as the server and storage

switches to effectively share a single IP and MAC address,

infrastructure. Two gigabit fiber links to a closet of, say,

which is used as the default route for a VLAN. In the event

100 switch ports issufficient for most business purposes.

that one core fails, those VLANs will still be accessible.

In the event that it’s not, you’re likely better off bonding

Finally, proper use of STP (Spanning-Tree Protocol) is

multiple 1Gbit links rather than upgrading to 10G for those

essential to proper network operation. A full discussion of

closets. As 10G drops in price, this will change, but forthese two technologies is beyond the scope of this guide,

now, it’s far cheaper to bond several 1Gbit ports than to

but correct configuration of these two elements will have a

add 10G capability to both the core and the edge.

significant effect on the resiliency and proper operation of

In the likely event that VoIP will be deployed, it may be

any Layer-3 switched network.beneficial to implement small modular switches at the
edge as well, allowing PoE (Power over Ethernet) modules
to be installed in the same switch as the non-PoE ports.

Storage networking
Once the core has been built, you can take on storage
networking. Although other technologies are available,

also a possibility. This allows a single port to be used for

when you link servers to...