Choose the Right Switches for Your Local Area Network
By Rolf Versluis
Mid-size and large organizations are entering another cycle of Local Area Network upgrades
due to two recent technology changes. One is that 10Gb Ethernet are now standard connections
on servers. The other is the widespread adoption of wireless devices like the iPad that has
put a strain on Wireless Local Area Networks. This is forcing the adoption of 10Gb Ethernet
for server and access layer uplink connectivity.
Because the LAN has to be upgraded, organizations are looking ahead a few years to see
what other technologies are going to have to be accommodated, and working with experienced
network designers to put together a comprehensive plan. There are many considerations to take
into account in order to get an optimal design for the Core, Distribution, and Access layer
upgrades, and specific Cisco switch choices are important in order to implement the design well.
Core Network Upgrades
The core network is the primary site where application servers are located. Most organizations
now have a combination of dedicated application servers alongside servers configured for hosting
virtual servers, usually running VMware ESXi. The older servers tend to have multiple Gigabit
Ethernet connections, so the core network switches are similar to the Cisco 6500 or a stack
of Cisco 3750 Gigabit switches, with 50-300 Gigabit Ethernet ports total.
New servers are shipping with 10 Gb Ethernet on the motherboard, and the price for 10
Gb Ethernet cards has dropped so much that 1 Gb for servers is becoming difficult to cost justify.
Especially since 10 Gb connections in the datacenter can be made with copper twinax cabling,
it is difficult to make the decision to purchase anything else.
This is combined with the trend to moving away from storage in the servers, usually called
Direct Attached Storage, and moving all storage into a fast and reliable storage array accessed
by iSCSI, Fibre Channel (FC), Fibre Channel over Ethernet (FCoE), or ATA over Ethernet (AoE).
Sometimes the storage array is accessed at the file level as Network Attached Storage (NAS)
by either CIFS or NFS.
It is much more cost-effective to access networked storage over 10G Ethernet connections than
1Gb Ethernet or even Fibre Channel because the price of a 10Gb Ethernet connection is much lower
than an equivalent Fibre Channel connection. Because the storage array can be backed up and
replicated to another site, it adds the additional benefit of improving business continuity capabilities.
The Cisco Nexus 5000 Series is equipped to support
expansion modules that can be used to increase the
number of 10 Gigabit Ethernet and FCoE ports or
connect to Fibre Channel SANs with 4/2/1-Gbps
Fibre Channel switch ports, or both.
If the organization is purchasing new storage arrays at the same time as the new servers,
they can be specified for 10Gb iSCSI, 10Gb FCoE, or 10Gb AoE, but if the storage arrays are
older Fibre Channel arrays, there has to be a provision made for connecting the new servers
to the old storage. This is where the Cisco Nexus 5000 switches come into play. The Nexus 5000's
have the ability to connect to FC storage arrays, and merge the FC stream into a 10 Gb FCoE
connection. This capability allows the organization to not have to purchase Fibre Channel Host
Bus Adapters for every new server, and also limits the size of the Fibre Channel Storage Area
Network that has to be maintained.
Not only can the Nexus 5000 provide Ethernet access to legacy storage for the new servers,
it can connect the older 1 Gb servers into the system as well. This is done by connecting Nexus
2000 fabric extenders into the Nexus 5000 at 10 Gb speed, putting the Nexus 2000 boxes at the
top of the rack of the older servers, and connecting the multitude of existing1 Gb Ethernet
to the Nexus 2000 boxes. This architecture provides high speed server and storage access at
the upgraded core of the network, as well as connectivity to new storage, legacy storage, and
older servers.
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